path: root/doc/rfc/rfc8620.txt

Internet Engineering Task Force (IETF)                        N. Jenkins
Request for Comments: 8620                                      Fastmail
Category: Standards Track                                      C. Newman
ISSN: 2070-1721                                                   Oracle
                                                               July 2019


               The JSON Meta Application Protocol (JMAP)

Abstract

   This document specifies a protocol for clients to efficiently query,
   fetch, and modify JSON-based data objects, with support for push
   notification of changes and fast resynchronisation and for out-of-
   band binary data upload/download.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8620.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.







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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
     1.2.  The Id Data Type  . . . . . . . . . . . . . . . . . . . .   6
     1.3.  The Int and UnsignedInt Data Types  . . . . . . . . . . .   6
     1.4.  The Date and UTCDate Data Types . . . . . . . . . . . . .   7
     1.5.  JSON as the Data Encoding Format  . . . . . . . . . . . .   7
     1.6.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   7
       1.6.1.  User  . . . . . . . . . . . . . . . . . . . . . . . .   7
       1.6.2.  Accounts  . . . . . . . . . . . . . . . . . . . . . .   7
       1.6.3.  Data Types and Records  . . . . . . . . . . . . . . .   8
     1.7.  The JMAP API Model  . . . . . . . . . . . . . . . . . . .   8
     1.8.  Vendor-Specific Extensions  . . . . . . . . . . . . . . .   9
   2.  The JMAP Session Resource . . . . . . . . . . . . . . . . . .   9
     2.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .  14
     2.2.  Service Autodiscovery . . . . . . . . . . . . . . . . . .  15
   3.  Structured Data Exchange  . . . . . . . . . . . . . . . . . .  16
     3.1.  Making an API Request . . . . . . . . . . . . . . . . . .  16
     3.2.  The Invocation Data Type  . . . . . . . . . . . . . . . .  16
     3.3.  The Request Object  . . . . . . . . . . . . . . . . . . .  16
       3.3.1.  Example Request . . . . . . . . . . . . . . . . . . .  18
     3.4.  The Response Object . . . . . . . . . . . . . . . . . . .  18
       3.4.1.  Example Response  . . . . . . . . . . . . . . . . . .  19
     3.5.  Omitting Arguments  . . . . . . . . . . . . . . . . . . .  19
     3.6.  Errors  . . . . . . . . . . . . . . . . . . . . . . . . .  19
       3.6.1.  Request-Level Errors  . . . . . . . . . . . . . . . .  20
       3.6.2.  Method-Level Errors . . . . . . . . . . . . . . . . .  21
     3.7.  References to Previous Method Results . . . . . . . . . .  22
     3.8.  Localisation of User-Visible Strings  . . . . . . . . . .  27
     3.9.  Security  . . . . . . . . . . . . . . . . . . . . . . . .  28
     3.10. Concurrency . . . . . . . . . . . . . . . . . . . . . . .  28
   4.  The Core/echo Method  . . . . . . . . . . . . . . . . . . . .  28
     4.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .  28
   5.  Standard Methods and Naming Convention  . . . . . . . . . . .  29
     5.1.  /get  . . . . . . . . . . . . . . . . . . . . . . . . . .  29
     5.2.  /changes  . . . . . . . . . . . . . . . . . . . . . . . .  30
     5.3.  /set  . . . . . . . . . . . . . . . . . . . . . . . . . .  34
     5.4.  /copy . . . . . . . . . . . . . . . . . . . . . . . . . .  40
     5.5.  /query  . . . . . . . . . . . . . . . . . . . . . . . . .  42
     5.6.  /queryChanges . . . . . . . . . . . . . . . . . . . . . .  48
     5.7.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  51
     5.8.  Proxy Considerations  . . . . . . . . . . . . . . . . . .  58
   6.  Binary Data . . . . . . . . . . . . . . . . . . . . . . . . .  58
     6.1.  Uploading Binary Data . . . . . . . . . . . . . . . . . .  59
     6.2.  Downloading Binary Data . . . . . . . . . . . . . . . . .  60
     6.3.  Blob/copy . . . . . . . . . . . . . . . . . . . . . . . .  61




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   7.  Push  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  62
     7.1.  The StateChange Object  . . . . . . . . . . . . . . . . .  63
       7.1.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  64
     7.2.  PushSubscription  . . . . . . . . . . . . . . . . . . . .  64
       7.2.1.  PushSubscription/get  . . . . . . . . . . . . . . . .  67
       7.2.2.  PushSubscription/set  . . . . . . . . . . . . . . . .  68
       7.2.3.  Example . . . . . . . . . . . . . . . . . . . . . . .  69
     7.3.  Event Source  . . . . . . . . . . . . . . . . . . . . . .  71
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  73
     8.1.  Transport Confidentiality . . . . . . . . . . . . . . . .  73
     8.2.  Authentication Scheme . . . . . . . . . . . . . . . . . .  73
     8.3.  Service Autodiscovery . . . . . . . . . . . . . . . . . .  73
     8.4.  JSON Parsing  . . . . . . . . . . . . . . . . . . . . . .  74
     8.5.  Denial of Service . . . . . . . . . . . . . . . . . . . .  74
     8.6.  Connection to Unknown Push Server . . . . . . . . . . . .  74
     8.7.  Push Encryption . . . . . . . . . . . . . . . . . . . . .  75
     8.8.  Traffic Analysis  . . . . . . . . . . . . . . . . . . . .  76
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  76
     9.1.  Assignment of jmap Service Name . . . . . . . . . . . . .  76
     9.2.  Registration of Well-Known URI Suffix for JMAP  . . . . .  76
     9.3.  Registration of the jmap URN Sub-namespace  . . . . . . .  77
     9.4.  Creation of "JMAP Capabilities" Registry  . . . . . . . .  77
       9.4.1.  Preliminary Community Review  . . . . . . . . . . . .  77
       9.4.2.  Submit Request to IANA  . . . . . . . . . . . . . . .  78
       9.4.3.  Designated Expert Review  . . . . . . . . . . . . . .  78
       9.4.4.  Change Procedures . . . . . . . . . . . . . . . . . .  78
       9.4.5.  JMAP Capabilities Registry Template . . . . . . . . .  79
       9.4.6.  Initial Registration for JMAP Core  . . . . . . . . .  79
       9.4.7.  Registration for JMAP Error Placeholder in JMAP
               Capabilities Registry . . . . . . . . . . . . . . . .  80
     9.5.  Creation of "JMAP Error Codes" Registry . . . . . . . . .  80
       9.5.1.  Expert Review . . . . . . . . . . . . . . . . . . . .  80
       9.5.2.  JMAP Error Codes Registry Template  . . . . . . . . .  81
       9.5.3.  Initial Contents for the JMAP Error Codes Registry  .  81
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  86
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  86
     10.2.  Informative References . . . . . . . . . . . . . . . . .  89
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  90













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1.  Introduction

   The JSON Meta Application Protocol (JMAP) is used for synchronising
   data, such as mail, calendars, or contacts, between a client and a
   server.  It is optimised for mobile and web environments and aims to
   provide a consistent interface to different data types.

   This specification is for the generic mechanism of data
   synchronisation.  Further specifications define the data models for
   different data types that may be synchronised via JMAP.

   JMAP is designed to make efficient use of limited network resources.
   Multiple API calls may be batched in a single request to the server,
   reducing round trips and improving battery life on mobile devices.
   Push connections remove the need for polling, and an efficient delta
   update mechanism ensures a minimum amount of data is transferred.

   JMAP is designed to be horizontally scalable to a very large number
   of users.  This is facilitated by separate endpoints for users after
   login, the separation of binary and structured data, and a data model
   for sharing that does not allow data dependencies between accounts.

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The underlying format used for this specification is JSON.
   Consequently, the terms "object" and "array" as well as the four
   primitive types (strings, numbers, booleans, and null) are to be
   interpreted as described in Section 1 of [RFC8259].  Unless otherwise
   noted, all the property names and values are case sensitive.

   Some examples in this document contain "partial" JSON documents used
   for illustrative purposes.  In these examples, three periods "..."
   are used to indicate a portion of the document that has been removed
   for compactness.

   For compatibility with publishing requirements, line breaks have been
   inserted inside long JSON strings, with the following continuation
   lines indented.  To form the valid JSON example, any line breaks
   inside a string must be replaced with a space and any other white
   space after the line break removed.





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   Unless otherwise specified, examples of API exchanges only show the
   methodCalls array of the Request object or the methodResponses array
   of the Response object.  For compactness, the rest of the Request/
   Response object is omitted.

   Type signatures are given for all JSON values in this document.  The
   following conventions are used:

   o  "*" - The type is undefined (the value could be any type, although
      permitted values may be constrained by the context of this value).

   o  "String" - The JSON string type.

   o  "Number" - The JSON number type.

   o  "Boolean" - The JSON boolean type.

   o  "A[B]" - A JSON object where the keys are all of type "A", and the
      values are all of type "B".

   o  "A[]" - An array of values of type "A".

   o  "A|B" - The value is either of type "A" or of type "B".

   Other types may also be given, with their representation defined
   elsewhere in this document.

   Object properties may also have a set of attributes defined along
   with the type signature.  These have the following meanings:

   o  "server-set" -- Only the server can set the value for this
      property.  The client MUST NOT send this property when creating a
      new object of this type.

   o  "immutable" -- The value MUST NOT change after the object is
      created.

   o  "default" -- (This is followed by a JSON value).  The value that
      will be used for this property if it is omitted in an argument or
      when creating a new object of this type.











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1.2.  The Id Data Type

   All record ids are assigned by the server and are immutable.

   Where "Id" is given as a data type, it means a "String" of at least 1
   and a maximum of 255 octets in size, and it MUST only contain
   characters from the "URL and Filename Safe" base64 alphabet, as
   defined in Section 5 of [RFC4648], excluding the pad character ("=").
   This means the allowed characters are the ASCII alphanumeric
   characters ("A-Za-z0-9"), hyphen ("-"), and underscore ("_").

   These characters are safe to use in almost any context (e.g.,
   filesystems, URIs, and IMAP atoms).  For maximum safety, servers
   SHOULD also follow defensive allocation strategies to avoid creating
   risks where glob completion or data type detection may be present
   (e.g., on filesystems or in spreadsheets).  In particular, it is wise
   to avoid:

   o  Ids starting with a dash

   o  Ids starting with digits

   o  Ids that contain only digits

   o  Ids that differ only by ASCII case (for example, A vs. a)

   o  the specific sequence of three characters "NIL" (because this
      sequence can be confused with the IMAP protocol expression of the
      null value)

   A good solution to these issues is to prefix every id with a single
   alphabetical character.

1.3.  The Int and UnsignedInt Data Types

   Where "Int" is given as a data type, it means an integer in the range
   -2^53+1 <= value <= 2^53-1, the safe range for integers stored in a
   floating-point double, represented as a JSON "Number".

   Where "UnsignedInt" is given as a data type, it means an "Int" where
   the value MUST be in the range 0 <= value <= 2^53-1.










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1.4.  The Date and UTCDate Data Types

   Where "Date" is given as a type, it means a string in "date-time"
   format [RFC3339].  To ensure a normalised form, the "time-secfrac"
   MUST always be omitted if zero, and any letters in the string (e.g.,
   "T" and "Z") MUST be uppercase.  For example,
   "2014-10-30T14:12:00+08:00".

   Where "UTCDate" is given as a type, it means a "Date" where the
   "time-offset" component MUST be "Z" (i.e., it must be in UTC time).
   For example, "2014-10-30T06:12:00Z".

1.5.  JSON as the Data Encoding Format

   JSON is a text-based data interchange format as specified in
   [RFC8259].  The Internet JSON (I-JSON) format defined in [RFC7493] is
   a strict subset of this, adding restrictions to avoid potentially
   confusing scenarios (for example, it mandates that an object MUST NOT
   have two members with the same name).

   All data sent from the client to the server or from the server to the
   client (except binary file upload/download) MUST be valid I-JSON
   according to the RFC and is therefore case sensitive and encoded in
   UTF-8 [RFC3629].

1.6.  Terminology

1.6.1.  User

   A user is a person accessing data via JMAP.  A user has a set of
   permissions determining the data that they can see.

1.6.2.  Accounts

   An account is a collection of data.  A single account may contain an
   arbitrary set of data types, for example, a collection of mail,
   contacts, and calendars.  Most JMAP methods take a mandatory
   "accountId" argument that specifies on which account the operations
   are to take place.

   An account is not the same as a user, although it is common for a
   primary account to directly belong to the user.  For example, you may
   have an account that contains data for a group or business, to which
   multiple users have access.







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   A single set of credentials may provide access to multiple accounts,
   for example, if another user is sharing their work calendar with the
   authenticated user or if there is a group mailbox for a support-desk
   inbox.

   In the event of a severe internal error, a server may have to
   reallocate ids or do something else that violates standard JMAP data
   constraints for an account.  In this situation, the data on the
   server is no longer compatible with cached data the client may have
   from before.  The server MUST treat this as though the account has
   been deleted and then recreated with a new account id.  Clients will
   then be forced to throw away any data with the old account id and
   refetch all data from scratch.

1.6.3.  Data Types and Records

   JMAP provides a uniform interface for creating, retrieving, updating,
   and deleting various types of objects.  A "data type" is a collection
   of named, typed properties, just like the schema for a database
   table.  Each instance of a data type is called a "record".

   The id of a record is immutable and assigned by the server.  The id
   MUST be unique among all records of the *same type* within the *same
   account*.  Ids may clash across accounts or for two records of
   different types within the same account.

1.7.  The JMAP API Model

   JMAP uses HTTP [RFC7230] to expose API, push, upload, and download
   resources.  All HTTP requests MUST use the "https://" scheme (HTTP
   over TLS [RFC2818]).  All HTTP requests MUST be authenticated.

   An authenticated client can fetch the user's Session object with
   details about the data and capabilities the server can provide as
   shown in Section 2.  The client may then exchange data with the
   server in the following ways:

   1.  The client may make an API request to the server to get or set
       structured data.  This request consists of an ordered series of
       method calls.  These are processed by the server, which then
       returns an ordered series of responses.  This is described in
       Sections 3, 4, and 5.

   2.  The client may download or upload binary files from/to the
       server.  This is detailed in Section 6.

   3.  The client may connect to a push channel on the server, to be
       notified when data has changed.  This is explained in Section 7.



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1.8.  Vendor-Specific Extensions

   Individual services will have custom features they wish to expose
   over JMAP.  This may take the form of extra data types and/or methods
   not in the spec, extra arguments to JMAP methods, or extra properties
   on existing data types (which may also appear in arguments to methods
   that take property names).

   The server can advertise custom extensions it supports by including
   the identifiers in the capabilities object.  Identifiers for vendor
   extensions MUST be a URL belonging to a domain owned by the vendor,
   to avoid conflict.  The URL SHOULD resolve to documentation for the
   changes the extension makes.

   The client MUST opt in to use an extension by passing the appropriate
   capability identifier in the "using" array of the Request object, as
   described in Section 3.3.  The server MUST only follow the
   specifications that are opted into and behave as though it does not
   implement anything else when processing a request.  This is to ensure
   compatibility with clients that don't know about a specific custom
   extension and for compatibility with future versions of JMAP.

2.  The JMAP Session Resource

   You need two things to connect to a JMAP server:

   1.  The URL for the JMAP Session resource.  This may be requested
       directly from the user or discovered automatically based on a
       username domain (see Section 2.2 below).

   2.  Credentials to authenticate with.  How to obtain credentials is
       out of scope for this document.

   A successful authenticated GET request to the JMAP Session resource
   MUST return a JSON-encoded *Session* object, giving details about the
   data and capabilities the server can provide to the client given
   those credentials.  It has the following properties:

   o  capabilities: "String[Object]"

      An object specifying the capabilities of this server.  Each key is
      a URI for a capability supported by the server.  The value for
      each of these keys is an object with further information about the
      server's capabilities in relation to that capability.

      The client MUST ignore any properties it does not understand.





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      The capabilities object MUST include a property called
      "urn:ietf:params:jmap:core".  The value of this property is an
      object that MUST contain the following information on server
      capabilities (suggested minimum values for limits are supplied
      that allow clients to make efficient use of the network):

      *  maxSizeUpload: "UnsignedInt"

         The maximum file size, in octets, that the server will accept
         for a single file upload (for any purpose).  Suggested minimum:
         50,000,000.

      *  maxConcurrentUpload: "UnsignedInt"

         The maximum number of concurrent requests the server will
         accept to the upload endpoint.  Suggested minimum: 4.

      *  maxSizeRequest: "UnsignedInt"

         The maximum size, in octets, that the server will accept for a
         single request to the API endpoint.  Suggested minimum:
         10,000,000.

      *  maxConcurrentRequests: "UnsignedInt"

         The maximum number of concurrent requests the server will
         accept to the API endpoint.  Suggested minimum: 4.

      *  maxCallsInRequest: "UnsignedInt"

         The maximum number of method calls the server will accept in a
         single request to the API endpoint.  Suggested minimum: 16.

      *  maxObjectsInGet: "UnsignedInt"

         The maximum number of objects that the client may request in a
         single /get type method call.  Suggested minimum: 500.

      *  maxObjectsInSet: "UnsignedInt"

         The maximum number of objects the client may send to create,
         update, or destroy in a single /set type method call.  This is
         the combined total, e.g., if the maximum is 10, you could not
         create 7 objects and destroy 6, as this would be 13 actions,
         which exceeds the limit.  Suggested minimum: 500.






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      *  collationAlgorithms: "String[]"

         A list of identifiers for algorithms registered in the
         collation registry, as defined in [RFC4790], that the server
         supports for sorting when querying records.

      Specifications for future capabilities will define their own
      properties on the capabilities object.

      Servers MAY advertise vendor-specific JMAP extensions, as
      described in Section 1.8.  To avoid conflict, an identifier for a
      vendor-specific extension MUST be a URL with a domain owned by the
      vendor.  Clients MUST opt in to any capability it wishes to use
      (see Section 3.3).

   o  accounts: "Id[Account]"

      A map of an account id to an Account object for each account (see
      Section 1.6.2) the user has access to.  An *Account* object has
      the following properties:

      *  name: "String"

         A user-friendly string to show when presenting content from
         this account, e.g., the email address representing the owner of
         the account.

      *  isPersonal: "Boolean"

         This is true if the account belongs to the authenticated user
         rather than a group account or a personal account of another
         user that has been shared with them.

      *  isReadOnly: "Boolean"

         This is true if the entire account is read-only.

      *  accountCapabilities: "String[Object]"

         The set of capability URIs for the methods supported in this
         account.  Each key is a URI for a capability that has methods
         you can use with this account.  The value for each of these
         keys is an object with further information about the account's
         permissions and restrictions with respect to this capability,
         as defined in the capability's specification.

         The client MUST ignore any properties it does not understand.




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         The server advertises the full list of capabilities it supports
         in the capabilities object, as defined above.  If the
         capability defines new methods, the server MUST include it in
         the accountCapabilities object if the user may use those
         methods with this account.  It MUST NOT include it in the
         accountCapabilities object if the user cannot use those methods
         with this account.

         For example, you may have access to your own account with mail,
         calendars, and contacts data and also a shared account that
         only has contacts data (a business address book, for example).
         In this case, the accountCapabilities property on the first
         account would include something like
         "urn:ietf:params:jmap:mail", "urn:ietf:params:jmap:calendars",
         and "urn:ietf:params:jmap:contacts", while the second account
         would just have the last of these.

         Attempts to use the methods defined in a capability with one of
         the accounts that does not support that capability are rejected
         with an "accountNotSupportedByMethod" error (see "Method-Level
         Errors", Section 3.6.2).

   o  primaryAccounts: "String[Id]"

      A map of capability URIs (as found in accountCapabilities) to the
      account id that is considered to be the user's main or default
      account for data pertaining to that capability.  If no account
      being returned belongs to the user, or in any other way there is
      no appropriate way to determine a default account, there MAY be no
      entry for a particular URI, even though that capability is
      supported by the server (and in the capabilities object).
      "urn:ietf:params:jmap:core" SHOULD NOT be present.

   o  username: "String"

      The username associated with the given credentials, or the empty
      string if none.

   o  apiUrl: "String"

      The URL to use for JMAP API requests.










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   o  downloadUrl: "String"

      The URL endpoint to use when downloading files, in URI Template
      (level 1) format [RFC6570].  The URL MUST contain variables called
      "accountId", "blobId", "type", and "name".  The use of these
      variables is described in Section 6.2.  Due to potential encoding
      issues with slashes in content types, it is RECOMMENDED to put the
      "type" variable in the query section of the URL.

   o  uploadUrl: "String"

      The URL endpoint to use when uploading files, in URI Template
      (level 1) format [RFC6570].  The URL MUST contain a variable
      called "accountId".  The use of this variable is described in
      Section 6.1.

   o  eventSourceUrl: "String"

      The URL to connect to for push events, as described in
      Section 7.3, in URI Template (level 1) format [RFC6570].  The URL
      MUST contain variables called "types", "closeafter", and "ping".
      The use of these variables is described in Section 7.3.

   o  state: "String"

      A (preferably short) string representing the state of this object
      on the server.  If the value of any other property on the Session
      object changes, this string will change.  The current value is
      also returned on the API Response object (see Section 3.4),
      allowing clients to quickly determine if the session information
      has changed (e.g., an account has been added or removed), so they
      need to refetch the object.

   To ensure future compatibility, other properties MAY be included on
   the Session object.  Clients MUST ignore any properties they are not
   expecting.

   Implementors must take care to avoid inappropriate caching of the
   Session object at the HTTP layer.  Since the client should only
   refetch when it detects there is a change (via the sessionState
   property of an API response), it is RECOMMENDED to disable HTTP
   caching altogether, for example, by setting "Cache-Control: no-cache,
   no-store, must-revalidate" on the response.








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2.1.  Example

   In the following example Session object, the user has access to their
   own mail and contacts via JMAP, as well as read-only access to shared
   mail from another user.  The server is advertising a custom
   "https://example.com/apis/foobar" capability.

   {
     "capabilities": {
       "urn:ietf:params:jmap:core": {
         "maxSizeUpload": 50000000,
         "maxConcurrentUpload": 8,
         "maxSizeRequest": 10000000,
         "maxConcurrentRequest": 8,
         "maxCallsInRequest": 32,
         "maxObjectsInGet": 256,
         "maxObjectsInSet": 128,
         "collationAlgorithms": [
           "i;ascii-numeric",
           "i;ascii-casemap",
           "i;unicode-casemap"
         ]
       },
       "urn:ietf:params:jmap:mail": {}
       "urn:ietf:params:jmap:contacts": {},
       "https://example.com/apis/foobar": {
         "maxFoosFinangled": 42
       }
     },
     "accounts": {
       "A13824": {
         "name": "john@example.com",
         "isPersonal": true,
         "isReadOnly": false,
         "accountCapabilities": {
           "urn:ietf:params:jmap:mail": {
             "maxMailboxesPerEmail": null,
             "maxMailboxDepth": 10,
             ...
           },
           "urn:ietf:params:jmap:contacts": {
             ...
           }
         }
       },






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       "A97813": {
         "name": "jane@example.com",
         "isPersonal": false,
         "isReadOnly": true,
         "accountCapabilities": {
           "urn:ietf:params:jmap:mail": {
             "maxMailboxesPerEmail": 1,
             "maxMailboxDepth": 10,
             ...
           }
         }
       }
     },
     "primaryAccounts": {
       "urn:ietf:params:jmap:mail": "A13824",
       "urn:ietf:params:jmap:contacts": "A13824"
     },
     "username": "john@example.com",
     "apiUrl": "https://jmap.example.com/api/",
     "downloadUrl": "https://jmap.example.com
       /download/{accountId}/{blobId}/{name}?accept={type}",
     "uploadUrl": "https://jmap.example.com/upload/{accountId}/",
     "eventSourceUrl": "https://jmap.example.com
       /eventsource/?types={types}&closeafter={closeafter}&ping={ping}",
     "state": "75128aab4b1b"
   }

2.2.  Service Autodiscovery

   There are two standardised autodiscovery methods in use for Internet
   protocols:

   o  DNS SRV (see [RFC2782], [RFC6186], and [RFC6764])

   o  .well-known/servicename (see [RFC8615])

   A JMAP-supporting host for the domain "example.com" SHOULD publish a
   SRV record "_jmap._tcp.example.com" that gives a hostname and port
   (usually port "443").  The JMAP Session resource is then
   "https://${hostname}[:${port}]/.well-known/jmap" (following any
   redirects).

   If the client has a username in the form of an email address, it MAY
   use the domain portion of this to attempt autodiscovery of the JMAP
   server.






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3.  Structured Data Exchange

   The client may make an API request to the server to get or set
   structured data.  This request consists of an ordered series of
   method calls.  These are processed by the server, which then returns
   an ordered series of responses.

3.1.  Making an API Request

   To make an API request, the client makes an authenticated POST
   request to the API resource, which is defined by the "apiUrl"
   property in the Session object (see Section 2).

   The request MUST be of type "application/json" and consist of a
   single JSON-encoded "Request" object, as defined in Section 3.3.  If
   successful, the response MUST also be of type "application/json" and
   consist of a single "Response" object, as defined in Section 3.4.

3.2.  The Invocation Data Type

   Method calls and responses are represented by the *Invocation* data
   type.  This is a tuple, represented as a JSON array containing three
   elements:

   1.  A "String" *name* of the method to call or of the response.

   2.  A "String[*]" object containing named *arguments* for that method
       or response.

   3.  A "String" *method call id*: an arbitrary string from the client
       to be echoed back with the responses emitted by that method call
       (a method may return 1 or more responses, as it may make implicit
       calls to other methods; all responses initiated by this method
       call get the same method call id in the response).

3.3.  The Request Object

   A *Request* object has the following properties:

   o  using: "String[]"

      The set of capabilities the client wishes to use.  The client MAY
      include capability identifiers even if the method calls it makes
      do not utilise those capabilities.  The server advertises the set
      of specifications it supports in the Session object (see
      Section 2), as keys on the "capabilities" property.





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   o  methodCalls: "Invocation[]"

      An array of method calls to process on the server.  The method
      calls MUST be processed sequentially, in order.

   o  createdIds: "Id[Id]" (optional)

      A map of a (client-specified) creation id to the id the server
      assigned when a record was successfully created.

      As described later in this specification, some records may have a
      property that contains the id of another record.  To allow more
      efficient network usage, you can set this property to reference a
      record created earlier in the same API request.  Since the real id
      is unknown when the request is created, the client can instead
      specify the creation id it assigned, prefixed with a "#" (see
      Section 5.3 for more details).

      As the server processes API requests, any time it successfully
      creates a new record, it adds the creation id to this map (see the
      "create" argument to /set in Section 5.3), with the server-
      assigned real id as the value.  If it comes across a reference to
      a creation id in a create/update, it looks it up in the map and
      replaces the reference with the real id, if found.

      The client can pass an initial value for this map as the
      "createdIds" property of the Request object.  This may be an empty
      object.  If given in the request, the response will also include a
      createdIds property.  This allows proxy servers to easily split a
      JMAP request into multiple JMAP requests to send to different
      servers.  For example, it could send the first two method calls to
      server A, then the third to server B, before sending the fourth to
      server A again.  By passing the createdIds of the previous
      response to the next request, it can ensure all of these still
      resolve.  See Section 5.8 for further discussion of proxy
      considerations.

   Future specifications MAY add further properties to the Request
   object to extend the semantics.  To ensure forwards compatibility, a
   server MUST ignore any other properties it does not understand on the
   JMAP Request object.










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3.3.1.  Example Request

{
  "using": [ "urn:ietf:params:jmap:core", "urn:ietf:params:jmap:mail" ],
  "methodCalls": [
    [ "method1", {
      "arg1": "arg1data",
      "arg2": "arg2data"
    }, "c1" ],
    [ "method2", {
      "arg1": "arg1data"
    }, "c2" ],
    [ "method3", {}, "c3" ]
  ]
}

3.4.  The Response Object

   A *Response* object has the following properties:

   o  methodResponses: "Invocation[]"

      An array of responses, in the same format as the "methodCalls" on
      the Request object.  The output of the methods MUST be added to
      the "methodResponses" array in the same order that the methods are
      processed.

   o  createdIds: "Id[Id]" (optional; only returned if given in the
      request)

      A map of a (client-specified) creation id to the id the server
      assigned when a record was successfully created.  This MUST
      include all creation ids passed in the original createdIds
      parameter of the Request object, as well as any additional ones
      added for newly created records.

   o  sessionState: "String"

      The current value of the "state" string on the Session object, as
      described in Section 2.  Clients may use this to detect if this
      object has changed and needs to be refetched.

   Unless otherwise specified, if the method call completed
   successfully, its response name is the same as the method name in the
   request.






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3.4.1.  Example Response

                   {
                     "methodResponses": [
                       [ "method1", {
                         "arg1": 3,
                         "arg2": "foo"
                       }, "c1" ],
                       [ "method2", {
                         "isBlah": true
                       }, "c2" ],
                       [ "anotherResponseFromMethod2", {
                         "data": 10,
                         "yetmoredata": "Hello"
                       }, "c2"],
                       [ "error", {
                         "type":"unknownMethod"
                       }, "c3" ]
                     ],
                     "sessionState": "75128aab4b1b"
                   }

3.5.  Omitting Arguments

   An argument to a method may be specified to have a default value.  If
   omitted by the client, the server MUST treat the method call the same
   as if the default value had been specified.  Similarly, the server
   MAY omit any argument in a response that has the default value.

   Unless otherwise specified in a method description, null is the
   default value for any argument in a request or response where this is
   allowed by the type signature.  Other arguments may only be omitted
   if an explicit default value is defined in the method description.

3.6.  Errors

   There are three different levels of granularity at which an error may
   be returned in JMAP.

   When an API request is made, the request as a whole may be rejected
   due to rate limiting, malformed JSON, request for an unknown
   capability, etc.  In this case, the entire request is rejected with
   an appropriate HTTP error response code and an additional JSON body
   with more detail for the client.

   Provided the request itself is syntactically valid (the JSON is valid
   and when decoded, it matches the type signature of a Request object),
   the methods within it are executed sequentially by the server.  Each



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   method may individually fail, for example, if invalid arguments are
   given or an unknown method name is called.

   Finally, methods that make changes to the server state often act upon
   a number of different records within a single call.  Each record
   change may be separately rejected with a SetError, as described in
   Section 5.3.

3.6.1.  Request-Level Errors

   When an HTTP error response is returned to the client, the server
   SHOULD return a JSON "problem details" object as the response body,
   as per [RFC7807].

   The following problem types are defined:

   o  "urn:ietf:params:jmap:error:unknownCapability"
      The client included a capability in the "using" property of the
      request that the server does not support.

   o  "urn:ietf:params:jmap:error:notJSON"
      The content type of the request was not "application/json" or the
      request did not parse as I-JSON.

   o  "urn:ietf:params:jmap:error:notRequest"
      The request parsed as JSON but did not match the type signature of
      the Request object.

   o  "urn:ietf:params:jmap:error:limit"
      The request was not processed as it would have exceeded one of the
      request limits defined on the capability object, such as
      maxSizeRequest, maxCallsInRequest, or maxConcurrentRequests.  A
      "limit" property MUST also be present on the "problem details"
      object, containing the name of the limit being applied.

3.6.1.1.  Example

       {
         "type": "urn:ietf:params:jmap:error:unknownCapability",
         "status": 400,
         "detail": "The Request object used capability
           'https://example.com/apis/foobar', which is not supported
           by this server."
       }







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   Another example:

     {
       "type": "urn:ietf:params:jmap:error:limit",
       "limit": "maxSizeRequest",
       "status": 400,
       "detail": "The request is larger than the server is willing to
                  process."
     }

3.6.2.  Method-Level Errors

   If a method encounters an error, the appropriate "error" response
   MUST be inserted at the current point in the "methodResponses" array
   and, unless otherwise specified, further processing MUST NOT happen
   within that method call.

   Any further method calls in the request MUST then be processed as
   normal.  Errors at the method level MUST NOT generate an HTTP-level
   error.

   An "error" response looks like this:

                         [ "error", {
                           "type": "unknownMethod"
                         }, "call-id" ]

   The response name is "error", and it MUST have a type property.
   Other properties may be present with further information; these are
   detailed in the error type descriptions where appropriate.

   With the exception of when the "serverPartialFail" error is returned,
   the externally visible state of the server MUST NOT have changed if
   an error is returned at the method level.

   The following error types are defined, which may be returned for any
   method call where appropriate:

   "serverUnavailable": Some internal server resource was temporarily
   unavailable.  Attempting the same operation later (perhaps after a
   backoff with a random factor) may succeed.

   "serverFail": An unexpected or unknown error occurred during the
   processing of the call.  A "description" property should provide more
   details about the error.  The method call made no changes to the
   server's state.  Attempting the same operation again is expected to
   fail again.  Contacting the service administrator is likely necessary
   to resolve this problem if it is persistent.



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   "serverPartialFail": Some, but not all, expected changes described by
   the method occurred.  The client MUST resynchronise impacted data to
   determine server state.  Use of this error is strongly discouraged.

   "unknownMethod": The server does not recognise this method name.

   "invalidArguments": One of the arguments is of the wrong type or is
   otherwise invalid, or a required argument is missing.  A
   "description" property MAY be present to help debug with an
   explanation of what the problem was.  This is a non-localised string,
   and it is not intended to be shown directly to end users.

   "invalidResultReference": The method used a result reference for one
   of its arguments (see Section 3.7), but this failed to resolve.

   "forbidden": The method and arguments are valid, but executing the
   method would violate an Access Control List (ACL) or other
   permissions policy.

   "accountNotFound": The accountId does not correspond to a valid
   account.

   "accountNotSupportedByMethod": The accountId given corresponds to a
   valid account, but the account does not support this method or data
   type.

   "accountReadOnly": This method modifies state, but the account is
   read-only (as returned on the corresponding Account object in the
   JMAP Session resource).

   Further possible errors for a particular method are specified in the
   method descriptions.

   Further general errors MAY be defined in future RFCs.  Should a
   client receive an error type it does not understand, it MUST treat it
   the same as the "serverFail" type.

3.7.  References to Previous Method Results

   To allow clients to make more efficient use of the network and avoid
   round trips, an argument to one method can be taken from the result
   of a previous method call in the same request.

   To do this, the client prefixes the argument name with "#" (an
   octothorpe).  The value is a ResultReference object as described
   below.  When processing a method call, the server MUST first check
   the arguments object for any names beginning with "#".  If found, the
   result reference should be resolved and the value used as the "real"



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   argument.  The method is then processed as normal.  If any result
   reference fails to resolve, the whole method MUST be rejected with an
   "invalidResultReference" error.  If an arguments object contains the
   same argument name in normal and referenced form (e.g., "foo" and
   "#foo"), the method MUST return an "invalidArguments" error.

   A *ResultReference* object has the following properties:

   o  resultOf: "String"

      The method call id (see Section 3.2) of a previous method call in
      the current request.

   o  name: "String"

      The required name of a response to that method call.

   o  path: "String"

      A pointer into the arguments of the response selected via the name
      and resultOf properties.  This is a JSON Pointer [RFC6901], except
      it also allows the use of "*" to map through an array (see the
      description below).

   To resolve:

   1.  Find the first response with a method call id identical to the
       "resultOf" property of the ResultReference in the
       "methodResponses" array from previously processed method calls in
       the same request.  If none, evaluation fails.

   2.  If the response name is not identical to the "name" property of
       the ResultReference, evaluation fails.

   3.  Apply the "path" to the arguments object of the response (the
       second item in the response array) following the JSON Pointer
       algorithm [RFC6901], except with the following addition in
       "Evaluation" (see Section 4):

       If the currently referenced value is a JSON array, the reference
       token may be exactly the single character "*", making the new
       referenced value the result of applying the rest of the JSON
       Pointer tokens to every item in the array and returning the
       results in the same order in a new array.  If the result of
       applying the rest of the pointer tokens to each item was itself
       an array, the contents of this array are added to the output
       rather than the array itself (i.e., the result is flattened from
       an array of arrays to a single array).  If the result of applying



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       the rest of the pointer tokens to a value was itself an array,
       its items should be included individually in the output rather
       than including the array itself (i.e., the result is flattened
       from an array of arrays to a single array).

   As a simple example, suppose we have the following API request
   "methodCalls":

                      [[ "Foo/changes", {
                          "accountId": "A1",
                          "sinceState": "abcdef"
                      }, "t0" ],
                      [ "Foo/get", {
                          "accountId": "A1",
                          "#ids": {
                              "resultOf": "t0",
                              "name": "Foo/changes",
                              "path": "/created"
                          }
                      }, "t1" ]]

   After executing the first method call, the "methodResponses" array
   is:

                      [[ "Foo/changes", {
                          "accountId": "A1",
                          "oldState": "abcdef",
                          "newState": "123456",
                          "hasMoreChanges": false,
                          "created": [ "f1", "f4" ],
                          "updated": [],
                          "destroyed": []
                      }, "t0" ]]

   To execute the "Foo/get" call, we look through the arguments and find
   there is one with a "#" prefix.  To resolve this, we apply the
   algorithm above:

   1.  Find the first response with method call id "t0".  The "Foo/
       changes" response fulfils this criterion.

   2.  Check that the response name is the same as in the result
       reference.  It is, so this is fine.

   3.  Apply the "path" as a JSON Pointer to the arguments object.  This
       simply selects the "created" property, so the result of
       evaluating is: [ "f1", "f4" ].




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   The JMAP server now continues to process the "Foo/get" call as though
   the arguments were:

                         {
                             "accountId": "A1",
                             "ids": [ "f1", "f4" ]
                         }

   Now, a more complicated example using the JMAP Mail data model: fetch
   the "from"/"date"/"subject" for every Email in the first 10 Threads
   in the inbox (sorted newest first):

      [[ "Email/query", {
        "accountId": "A1",
        "filter": { "inMailbox": "id_of_inbox" },
        "sort": [{ "property": "receivedAt", "isAscending": false }],
        "collapseThreads": true,
        "position": 0,
        "limit": 10,
        "calculateTotal": true
      }, "t0" ],
      [ "Email/get", {
        "accountId": "A1",
        "#ids": {
          "resultOf": "t0",
          "name": "Email/query",
          "path": "/ids"
        },
        "properties": [ "threadId" ]
      }, "t1" ],
      [ "Thread/get", {
        "accountId": "A1",
        "#ids": {
          "resultOf": "t1",
          "name": "Email/get",
          "path": "/list/*/threadId"
        }
      }, "t2" ],
      [ "Email/get", {
        "accountId": "A1",
        "#ids": {
          "resultOf": "t2",
          "name": "Thread/get",
          "path": "/list/*/emailIds"
        },
        "properties": [ "from", "receivedAt", "subject" ]
      }, "t3" ]]




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   After executing the first 3 method calls, the "methodResponses" array
   might be:

       [[ "Email/query", {
           "accountId": "A1",
           "queryState": "abcdefg",
           "canCalculateChanges": true,
           "position": 0,
           "total": 101,
           "ids": [ "msg1023", "msg223", "msg110", "msg93", "msg91",
               "msg38", "msg36", "msg33", "msg11", "msg1" ]
       }, "t0" ],
       [ "Email/get", {
           "accountId": "A1",
           "state": "123456",
           "list": [{
               "id": "msg1023",
               "threadId": "trd194"
           }, {
               "id": "msg223",
               "threadId": "trd114"
           },
           ...
           ],
           "notFound": []
       }, "t1" ],
       [ "Thread/get", {
           "accountId": "A1",
           "state": "123456",
           "list": [{
               "id": "trd194",
               "emailIds": [ "msg1020", "msg1021", "msg1023" ]
           }, {
               "id": "trd114",
               "emailIds": [ "msg201", "msg223" ]
           },
           ...
           ],
           "notFound": []
       }, "t2" ]]

   To execute the final "Email/get" call, we look through the arguments
   and find there is one with a "#" prefix.  To resolve this, we apply
   the algorithm:

   1.  Find the first response with method call id "t2".  The "Thread/
       get" response fulfils this criterion.




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   2.  "Thread/get" is the name specified in the result reference, so
       this is fine.

   3.  Apply the "path" as a JSON Pointer to the arguments object.
       Token by token:

       1.  "list": get the array of thread objects

       2.  "*": for each of the items in the array:

           a.  "emailIds": get the array of Email ids

           b.  Concatenate these into a single array of all the ids in
               the result.

   The JMAP server now continues to process the "Email/get" call as
   though the arguments were:

{
    "accountId": "A1",
    "ids": [ "msg1020", "msg1021", "msg1023", "msg201", "msg223", ... ],
    "properties": [ "from", "receivedAt", "subject" ]
}

   The ResultReference performs a similar role to that of the creation
   id, in that it allows a chained method call to refer to information
   not available when the request is generated.  However, they are
   different things and not interchangeable; the only commonality is the
   octothorpe used to indicate them.

3.8.  Localisation of User-Visible Strings

   If returning a custom string to be displayed to the user, for
   example, an error message, the server SHOULD use information from the
   Accept-Language header of the request (as defined in Section 5.3.5 of
   [RFC7231]) to choose the best available localisation.  The Content-
   Language header of the response (see Section 3.1.3.2 of [RFC7231])
   SHOULD indicate the language being used for user-visible strings.

   For example, suppose a request was made with the following header:

       Accept-Language: fr-CH, fr;q=0.9, de;q=0.8, en;q=0.7, *;q=0.5

   and a method generated an error to display to the user.  The server
   has translations of the error message in English and German.  Looking
   at the Accept-Language header, the user's preferred language is
   French.  Since we don't have a translation for this, we look at the




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   next most preferred, which is German.  We have a German translation,
   so the server returns this and indicates the language chosen in a
   Content-Language header like so:

                           Content-Language: de

3.9.  Security

   As always, the server must be strict about data received from the
   client.  Arguments need to be checked for validity; a malicious user
   could attempt to find an exploit through the API.  In case of invalid
   arguments (unknown/insufficient/wrong type for data, etc.), the
   method MUST return an "invalidArguments" error and terminate.

3.10.  Concurrency

   Method calls within a single request MUST be executed in order.
   However, method calls from different concurrent API requests may be
   interleaved.  This means that the data on the server may change
   between two method calls within a single API request.

4.  The Core/echo Method

   The "Core/echo" method returns exactly the same arguments as it is
   given.  It is useful for testing if you have a valid authenticated
   connection to a JMAP API endpoint.

4.1.  Example

   Request:

                             [[ "Core/echo", {
                               "hello": true,
                               "high": 5
                             }, "b3ff" ]]

   Response:

                             [[ "Core/echo", {
                               "hello": true,
                               "high": 5
                             }, "b3ff" ]]









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5.  Standard Methods and Naming Convention

   JMAP provides a uniform interface for creating, retrieving, updating,
   and deleting objects of a particular type.  For a "Foo" data type,
   records of that type would be fetched via a "Foo/get" call and
   modified via a "Foo/set" call.  Delta updates may be fetched via a
   "Foo/changes" call.  These methods all follow a standard format as
   described below.

   Some types may not have all these methods.  Specifications defining
   types MUST specify which methods are available for the type.

5.1.  /get

   Objects of type Foo are fetched via a call to "Foo/get".

   It takes the following arguments:

   o  accountId: "Id"

      The id of the account to use.

   o  ids: "Id[]|null"

      The ids of the Foo objects to return.  If null, then *all* records
      of the data type are returned, if this is supported for that data
      type and the number of records does not exceed the
      "maxObjectsInGet" limit.

   o  properties: "String[]|null"

      If supplied, only the properties listed in the array are returned
      for each Foo object.  If null, all properties of the object are
      returned.  The id property of the object is *always* returned,
      even if not explicitly requested.  If an invalid property is
      requested, the call MUST be rejected with an "invalidArguments"
      error.

   The response has the following arguments:

   o  accountId: "Id"

      The id of the account used for the call.








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   o  state: "String"

      A (preferably short) string representing the state on the server
      for *all* the data of this type in the account (not just the
      objects returned in this call).  If the data changes, this string
      MUST change.  If the Foo data is unchanged, servers SHOULD return
      the same state string on subsequent requests for this data type.
      When a client receives a response with a different state string to
      a previous call, it MUST either throw away all currently cached
      objects for the type or call "Foo/changes" to get the exact
      changes.

   o  list: "Foo[]"

      An array of the Foo objects requested.  This is the *empty array*
      if no objects were found or if the "ids" argument passed in was
      also an empty array.  The results MAY be in a different order to
      the "ids" in the request arguments.  If an identical id is
      included more than once in the request, the server MUST only
      include it once in either the "list" or the "notFound" argument of
      the response.

   o  notFound: "Id[]"

      This array contains the ids passed to the method for records that
      do not exist.  The array is empty if all requested ids were found
      or if the "ids" argument passed in was either null or an empty
      array.

   The following additional error may be returned instead of the "Foo/
   get" response:

   "requestTooLarge": The number of ids requested by the client exceeds
   the maximum number the server is willing to process in a single
   method call.

5.2.  /changes

   When the state of the set of Foo records in an account changes on the
   server (whether due to creation, updates, or deletion), the "state"
   property of the "Foo/get" response will change.  The "Foo/changes"
   method allows a client to efficiently update the state of its Foo
   cache to match the new state on the server.  It takes the following
   arguments:

   o  accountId: "Id"

      The id of the account to use.



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   o  sinceState: "String"

      The current state of the client.  This is the string that was
      returned as the "state" argument in the "Foo/get" response.  The
      server will return the changes that have occurred since this
      state.

   o  maxChanges: "UnsignedInt|null"

      The maximum number of ids to return in the response.  The server
      MAY choose to return fewer than this value but MUST NOT return
      more.  If not given by the client, the server may choose how many
      to return.  If supplied by the client, the value MUST be a
      positive integer greater than 0.  If a value outside of this range
      is given, the server MUST reject the call with an
      "invalidArguments" error.

   The response has the following arguments:

   o  accountId: "Id"

      The id of the account used for the call.

   o  oldState: "String"

      This is the "sinceState" argument echoed back; it's the state from
      which the server is returning changes.

   o  newState: "String"

      This is the state the client will be in after applying the set of
      changes to the old state.

   o  hasMoreChanges: "Boolean"

      If true, the client may call "Foo/changes" again with the
      "newState" returned to get further updates.  If false, "newState"
      is the current server state.

   o  created: "Id[]"

      An array of ids for records that have been created since the old
      state.

   o  updated: "Id[]"

      An array of ids for records that have been updated since the old
      state.



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   o  destroyed: "Id[]"

      An array of ids for records that have been destroyed since the old
      state.

   If a record has been created AND updated since the old state, the
   server SHOULD just return the id in the "created" list but MAY return
   it in the "updated" list as well.

   If a record has been updated AND destroyed since the old state, the
   server SHOULD just return the id in the "destroyed" list but MAY
   return it in the "updated" list as well.

   If a record has been created AND destroyed since the old state, the
   server SHOULD remove the id from the response entirely.  However, it
   MAY include it in just the "destroyed" list or in both the
   "destroyed" and "created" lists.

   If a "maxChanges" is supplied, or set automatically by the server,
   the server MUST ensure the number of ids returned across "created",
   "updated", and "destroyed" does not exceed this limit.  If there are
   more changes than this between the client's state and the current
   server state, the server SHOULD generate an update to take the client
   to an intermediate state, from which the client can continue to call
   "Foo/changes" until it is fully up to date.  If it is unable to
   calculate an intermediate state, it MUST return a
   "cannotCalculateChanges" error response instead.

   When generating intermediate states, the server may choose how to
   divide up the changes.  For many types, it will provide a better user
   experience to return the more recent changes first, as this is more
   likely to be what the user is most interested in.  The client can
   then continue to page in the older changes while the user is viewing
   the newer data.  For example, suppose a server went through the
   following states:

                           A -> B -> C -> D -> E

   And a client asks for changes from state "B".  The server might first
   get the ids of records created, updated, or destroyed between states
   D and E, returning them with:

                           state: "B-D-E"
                           hasMoreChanges: true







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   The client will then ask for the change from state "B-D-E", and the
   server can return the changes between states C and D, returning:

                           state: "B-C-E"
                           hasMoreChanges: true

   Finally, the client will request the changes from "B-C-E", and the
   server can return the changes between states B and C, returning:

                           state: "E"
                           hasMoreChanges: false

   Should the state on the server be modified in the middle of all this
   (to "F"), the server still does the same, but now when the update to
   state "E" is returned, it would indicate that it still has more
   changes for the client to fetch.

   Where multiple changes to a record are split across different
   intermediate states, the server MUST NOT return a record as created
   after a response that deems it as updated or destroyed, and it MUST
   NOT return a record as destroyed before a response that deems it as
   created or updated.  The server may have to coalesce multiple changes
   to a record to satisfy this requirement.

   The following additional errors may be returned instead of the "Foo/
   changes" response:

   "cannotCalculateChanges": The server cannot calculate the changes
   from the state string given by the client.  Usually, this is due to
   the client's state being too old or the server being unable to
   produce an update to an intermediate state when there are too many
   updates.  The client MUST invalidate its Foo cache.

   Maintaining state to allow calculation of "Foo/changes" can be
   expensive for the server, but always returning
   "cannotCalculateChanges" severely increases network traffic and
   resource usage for the client.  To allow efficient sync, servers
   SHOULD be able to calculate changes from any state string that was
   given to a client within the last 30 days (but of course may support
   calculating updates from states older than this).











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5.3.  /set

   Modifying the state of Foo objects on the server is done via the
   "Foo/set" method.  This encompasses creating, updating, and
   destroying Foo records.  This allows the server to sort out ordering
   and dependencies that may exist if doing multiple operations at once
   (for example, to ensure there is always a minimum number of a certain
   record type).

   The "Foo/set" method takes the following arguments:

   o  accountId: "Id"

      The id of the account to use.

   o  ifInState: "String|null"

      This is a state string as returned by the "Foo/get" method
      (representing the state of all objects of this type in the
      account).  If supplied, the string must match the current state;
      otherwise, the method will be aborted and a "stateMismatch" error
      returned.  If null, any changes will be applied to the current
      state.

   o  create: "Id[Foo]|null"

      A map of a *creation id* (a temporary id set by the client) to Foo
      objects, or null if no objects are to be created.

      The Foo object type definition may define default values for
      properties.  Any such property may be omitted by the client.

      The client MUST omit any properties that may only be set by the
      server (for example, the "id" property on most object types).

   o  update: "Id[PatchObject]|null"

      A map of an id to a Patch object to apply to the current Foo
      object with that id, or null if no objects are to be updated.

      A *PatchObject* is of type "String[*]" and represents an unordered
      set of patches.  The keys are a path in JSON Pointer format
      [RFC6901], with an implicit leading "/" (i.e., prefix each key
      with "/" before applying the JSON Pointer evaluation algorithm).

      All paths MUST also conform to the following restrictions; if
      there is any violation, the update MUST be rejected with an
      "invalidPatch" error:



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      *  The pointer MUST NOT reference inside an array (i.e., you MUST
         NOT insert/delete from an array; the array MUST be replaced in
         its entirety instead).

      *  All parts prior to the last (i.e., the value after the final
         slash) MUST already exist on the object being patched.

      *  There MUST NOT be two patches in the PatchObject where the
         pointer of one is the prefix of the pointer of the other, e.g.,
         "alerts/1/offset" and "alerts".

      The value associated with each pointer determines how to apply
      that patch:

      *  If null, set to the default value if specified for this
         property; otherwise, remove the property from the patched
         object.  If the key is not present in the parent, this a no-op.

      *  Anything else: The value to set for this property (this may be
         a replacement or addition to the object being patched).

      Any server-set properties MAY be included in the patch if their
      value is identical to the current server value (before applying
      the patches to the object).  Otherwise, the update MUST be
      rejected with an "invalidProperties" SetError.

      This patch definition is designed such that an entire Foo object
      is also a valid PatchObject.  The client may choose to optimise
      network usage by just sending the diff or may send the whole
      object; the server processes it the same either way.

   o  destroy: "Id[]|null"

      A list of ids for Foo objects to permanently delete, or null if no
      objects are to be destroyed.

   Each creation, modification, or destruction of an object is
   considered an atomic unit.  It is permissible for the server to
   commit changes to some objects but not others; however, it MUST NOT
   only commit part of an update to a single record (e.g., update a
   "name" property but not a "count" property, if both are supplied in
   the update object).

   The final state MUST be valid after the "Foo/set" is finished;
   however, the server may have to transition through invalid
   intermediate states (not exposed to the client) while processing the
   individual create/update/destroy requests.  For example, suppose
   there is a "name" property that must be unique.  A single method call



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   could rename an object A => B and simultaneously rename another
   object B => A.  If the final state is valid, this is allowed.
   Otherwise, each creation, modification, or destruction of an object
   should be processed sequentially and accepted/rejected based on the
   current server state.

   If a create, update, or destroy is rejected, the appropriate error
   MUST be added to the notCreated/notUpdated/notDestroyed property of
   the response, and the server MUST continue to the next create/update/
   destroy.  It does not terminate the method.

   If an id given cannot be found, the update or destroy MUST be
   rejected with a "notFound" set error.

   The server MAY skip an update (rejecting it with a "willDestroy"
   SetError) if that object is destroyed in the same /set request.

   Some records may hold references to other records (foreign keys).
   That reference may be set (via create or update) in the same request
   as the referenced record is created.  To do this, the client refers
   to the new record using its creation id prefixed with a "#".  The
   order of the method calls in the request by the client MUST be such
   that the record being referenced is created in the same or an earlier
   call.  Thus, the server never has to look ahead.  Instead, while
   processing a request, the server MUST keep a simple map for the
   duration of the request of creation id to record id for each newly
   created record, so it can substitute in the correct value if
   necessary in later method calls.  In the case of records with
   references to the same type, the server MUST order the creates and
   updates within a single method call so that creates happen before
   their creation ids are referenced by another create/update/destroy in
   the same call.

   Creation ids are not scoped by type but are a single map for all
   types.  A client SHOULD NOT reuse a creation id anywhere in the same
   API request.  If a creation id is reused, the server MUST map the
   creation id to the most recently created item with that id.  To allow
   easy proxying of API requests, an initial set of creation id to real
   id values may be passed with a request (see "The Request Object",
   Section 3.3) and the final state of the map passed out with the
   response (see "The Response Object", Section 3.4).

   The response has the following arguments:

   o  accountId: "Id"

      The id of the account used for the call.




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   o  oldState: "String|null"

      The state string that would have been returned by "Foo/get" before
      making the requested changes, or null if the server doesn't know
      what the previous state string was.

   o  newState: "String"

      The state string that will now be returned by "Foo/get".

   o  created: "Id[Foo]|null"

      A map of the creation id to an object containing any properties of
      the created Foo object that were not sent by the client.  This
      includes all server-set properties (such as the "id" in most
      object types) and any properties that were omitted by the client
      and thus set to a default by the server.

      This argument is null if no Foo objects were successfully created.

   o  updated: "Id[Foo|null]|null"

      The keys in this map are the ids of all Foos that were
      successfully updated.

      The value for each id is a Foo object containing any property that
      changed in a way *not* explicitly requested by the PatchObject
      sent to the server, or null if none.  This lets the client know of
      any changes to server-set or computed properties.

      This argument is null if no Foo objects were successfully updated.

   o  destroyed: "Id[]|null"

      A list of Foo ids for records that were successfully destroyed, or
      null if none.

   o  notCreated: "Id[SetError]|null"

      A map of the creation id to a SetError object for each record that
      failed to be created, or null if all successful.

   o  notUpdated: "Id[SetError]|null"

      A map of the Foo id to a SetError object for each record that
      failed to be updated, or null if all successful.





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   o  notDestroyed: "Id[SetError]|null"

      A map of the Foo id to a SetError object for each record that
      failed to be destroyed, or null if all successful.

   A *SetError* object has the following properties:

   o  type: "String"

      The type of error.

   o  description: "String|null"

      A description of the error to help with debugging that includes an
      explanation of what the problem was.  This is a non-localised
      string and is not intended to be shown directly to end users.

   The following SetError types are defined and may be returned for set
   operations on any record type where appropriate:

   o  "forbidden": (create; update; destroy).  The create/update/destroy
      would violate an ACL or other permissions policy.

   o  "overQuota": (create; update).  The create would exceed a server-
      defined limit on the number or total size of objects of this type.

   o  "tooLarge": (create; update).  The create/update would result in
      an object that exceeds a server-defined limit for the maximum size
      of a single object of this type.

   o  "rateLimit": (create).  Too many objects of this type have been
      created recently, and a server-defined rate limit has been
      reached.  It may work if tried again later.

   o  "notFound": (update; destroy).  The id given to update/destroy
      cannot be found.

   o  "invalidPatch": (update).  The PatchObject given to update the
      record was not a valid patch (see the patch description).

   o  "willDestroy": (update).  The client requested that an object be
      both updated and destroyed in the same /set request, and the
      server has decided to therefore ignore the update.








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   o  "invalidProperties": (create; update).  The record given is
      invalid in some way.  For example:

      *  It contains properties that are invalid according to the type
         specification of this record type.

      *  It contains a property that may only be set by the server
         (e.g., "id") and is different to the current value.  Note, to
         allow clients to pass whole objects back, it is not an error to
         include a server-set property in an update as long as the value
         is identical to the current value on the server.

      *  There is a reference to another record (foreign key), and the
         given id does not correspond to a valid record.

      The SetError object SHOULD also have a property called
      "properties" of type "String[]" that lists *all* the properties
      that were invalid.

      Individual methods MAY specify more specific errors for certain
      conditions that would otherwise result in an invalidProperties
      error.  If the condition of one of these is met, it MUST be
      returned instead of the invalidProperties error.

   o  "singleton": (create; destroy).  This is a singleton type, so you
      cannot create another one or destroy the existing one.

   Other possible SetError types MAY be given in specific method
   descriptions.  Other properties MAY also be present on the SetError
   object, as described in the relevant methods.

   The following additional errors may be returned instead of the "Foo/
   set" response:

   "requestTooLarge": The total number of objects to create, update, or
   destroy exceeds the maximum number the server is willing to process
   in a single method call.

   "stateMismatch": An "ifInState" argument was supplied, and it does
   not match the current state.











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5.4.  /copy

   The only way to move Foo records *between* two different accounts is
   to copy them using the "Foo/copy" method; once the copy has
   succeeded, delete the original.  The "onSuccessDestroyOriginal"
   argument allows you to try to do this in one method call; however,
   note that the two different actions are not atomic, so it is possible
   for the copy to succeed but the original not to be destroyed for some
   reason.

   The copy is conceptually in three phases:

   1.  Reading the current values from the "from" account.

   2.  Writing the new copies to the other account.

   3.  Destroying the originals in the "from" account, if requested.

   Data may change in between phases due to concurrent requests.

   The "Foo/copy" method takes the following arguments:

   o  fromAccountId: "Id"

      The id of the account to copy records from.

   o  ifFromInState: "String|null"

      This is a state string as returned by the "Foo/get" method.  If
      supplied, the string must match the current state of the account
      referenced by the fromAccountId when reading the data to be
      copied; otherwise, the method will be aborted and a
      "stateMismatch" error returned.  If null, the data will be read
      from the current state.

   o  accountId: "Id"

      The id of the account to copy records to.  This MUST be different
      to the "fromAccountId".

   o  ifInState: "String|null"

      This is a state string as returned by the "Foo/get" method.  If
      supplied, the string must match the current state of the account
      referenced by the accountId; otherwise, the method will be aborted
      and a "stateMismatch" error returned.  If null, any changes will
      be applied to the current state.




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   o  create: "Id[Foo]"

      A map of the *creation id* to a Foo object.  The Foo object MUST
      contain an "id" property, which is the id (in the fromAccount) of
      the record to be copied.  When creating the copy, any other
      properties included are used instead of the current value for that
      property on the original.

   o  onSuccessDestroyOriginal: "Boolean" (default: false)

      If true, an attempt will be made to destroy the original records
      that were successfully copied: after emitting the "Foo/copy"
      response, but before processing the next method, the server MUST
      make a single call to "Foo/set" to destroy the original of each
      successfully copied record; the output of this is added to the
      responses as normal, to be returned to the client.

   o  destroyFromIfInState: "String|null"

      This argument is passed on as the "ifInState" argument to the
      implicit "Foo/set" call, if made at the end of this request to
      destroy the originals that were successfully copied.

   Each record copy is considered an atomic unit that may succeed or
   fail individually.

   The response has the following arguments:

   o  fromAccountId: "Id"

      The id of the account records were copied from.

   o  accountId: "Id"

      The id of the account records were copied to.

   o  oldState: "String|null"

      The state string that would have been returned by "Foo/get" on the
      account records that were copied to before making the requested
      changes, or null if the server doesn't know what the previous
      state string was.

   o  newState: "String"

      The state string that will now be returned by "Foo/get" on the
      account records were copied to.




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   o  created: "Id[Foo]|null"

      A map of the creation id to an object containing any properties of
      the copied Foo object that are set by the server (such as the "id"
      in most object types; note, the id is likely to be different to
      the id of the object in the account it was copied from).

      This argument is null if no Foo objects were successfully copied.

   o  notCreated: "Id[SetError]|null"

      A map of the creation id to a SetError object for each record that
      failed to be copied, or null if none.

   The SetError may be any of the standard set errors returned for a
   create or update.  In addition, the following SetError is defined:

   "alreadyExists": The server forbids duplicates, and the record
   already exists in the target account.  An "existingId" property of
   type "Id" MUST be included on the SetError object with the id of the
   existing record.

   The following additional errors may be returned instead of the "Foo/
   copy" response:

   "fromAccountNotFound": The "fromAccountId" does not correspond to a
   valid account.

   "fromAccountNotSupportedByMethod": The "fromAccountId" given
   corresponds to a valid account, but the account does not support this
   data type.

   "stateMismatch": An "ifInState" argument was supplied and it does not
   match the current state, or an "ifFromInState" argument was supplied
   and it does not match the current state in the from account.

5.5.  /query

   For data sets where the total amount of data is expected to be very
   small, clients can just fetch the complete set of data and then do
   any sorting/filtering locally.  However, for large data sets (e.g.,
   multi-gigabyte mailboxes), the client needs to be able to
   search/sort/window the data type on the server.

   A query on the set of Foos in an account is made by calling "Foo/
   query".  This takes a number of arguments to determine which records
   to include, how they should be sorted, and which part of the result




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   should be returned (the full list may be *very* long).  The result is
   returned as a list of Foo ids.

   A call to "Foo/query" takes the following arguments:

   o  accountId: "Id"

      The id of the account to use.

   o  filter: "FilterOperator|FilterCondition|null"

      Determines the set of Foos returned in the results.  If null, all
      objects in the account of this type are included in the results.
      A *FilterOperator* object has the following properties:

      *  operator: "String"

         This MUST be one of the following strings:

         +  "AND": All of the conditions must match for the filter to
            match.

         +  "OR": At least one of the conditions must match for the
            filter to match.

         +  "NOT": None of the conditions must match for the filter to
            match.

      *  conditions: "(FilterOperator|FilterCondition)[]"

         The conditions to evaluate against each record.

      A *FilterCondition* is an "object" whose allowed properties and
      semantics depend on the data type and is defined in the /query
      method specification for that type.  It MUST NOT have an
      "operator" property.

   o  sort: "Comparator[]|null"

      Lists the names of properties to compare between two Foo records,
      and how to compare them, to determine which comes first in the
      sort.  If two Foo records have an identical value for the first
      comparator, the next comparator will be considered, and so on.  If
      all comparators are the same (this includes the case where an
      empty array or null is given as the "sort" argument), the sort
      order is server dependent, but it MUST be stable between calls to
      "Foo/query".  A *Comparator* has the following properties:




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      *  property: "String"

         The name of the property on the Foo objects to compare.

      *  isAscending: "Boolean" (optional; default: true)

         If true, sort in ascending order.  If false, reverse the
         comparator's results to sort in descending order.

      *  collation: "String" (optional; default is server-dependent)

         The identifier, as registered in the collation registry defined
         in [RFC4790], for the algorithm to use when comparing the order
         of strings.  The algorithms the server supports are advertised
         in the capabilities object returned with the Session object
         (see Section 2).

         If omitted, the default algorithm is server dependent, but:

         1.  It MUST be unicode-aware.

         2.  It MAY be selected based on an Accept-Language header in
             the request (as defined in [RFC7231], Section 5.3.5) or
             out-of-band information about the user's language/locale.

         3.  It SHOULD be case insensitive where such a concept makes
             sense for a language/locale.  Where the user's language is
             unknown, it is RECOMMENDED to follow the advice in
             Section 5.2.3 of [RFC8264].

         The "i;unicode-casemap" collation [RFC5051] and the Unicode
         Collation Algorithm (<http://www.unicode.org/reports/tr10/>)
         are two examples that fulfil these criterion and provide
         reasonable behaviour for a large number of languages.

         When the property being compared is not a string, the
         "collation" property is ignored, and the following comparison
         rules apply based on the type.  In ascending order:

         +  "Boolean": false comes before true.

         +  "Number": A lower number comes before a higher number.

         +  "Date"/"UTCDate": The earlier date comes first.

      The Comparator object may also have additional properties as
      required for specific sort operations defined in a type's /query
      method.



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   o  position: "Int" (default: 0)

      The zero-based index of the first id in the full list of results
      to return.

      If a negative value is given, it is an offset from the end of the
      list.  Specifically, the negative value MUST be added to the total
      number of results given the filter, and if still negative, it's
      clamped to "0".  This is now the zero-based index of the first id
      to return.

      If the index is greater than or equal to the total number of
      objects in the results list, then the "ids" array in the response
      will be empty, but this is not an error.

   o  anchor: "Id|null"

      A Foo id.  If supplied, the "position" argument is ignored.  The
      index of this id in the results will be used in combination with
      the "anchorOffset" argument to determine the index of the first
      result to return (see below for more details).

   o  anchorOffset: "Int" (default: 0)

      The index of the first result to return relative to the index of
      the anchor, if an anchor is given.  This MAY be negative.  For
      example, "-1" means the Foo immediately preceding the anchor is
      the first result in the list returned (see below for more
      details).

   o  limit: "UnsignedInt|null"

      The maximum number of results to return.  If null, no limit
      presumed.  The server MAY choose to enforce a maximum "limit"
      argument.  In this case, if a greater value is given (or if it is
      null), the limit is clamped to the maximum; the new limit is
      returned with the response so the client is aware.  If a negative
      value is given, the call MUST be rejected with an
      "invalidArguments" error.

   o  calculateTotal: "Boolean" (default: false)

      Does the client wish to know the total number of results in the
      query?  This may be slow and expensive for servers to calculate,
      particularly with complex filters, so clients should take care to
      only request the total when needed.





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   If an "anchor" argument is given, the anchor is looked for in the
   results after filtering and sorting.  If found, the "anchorOffset" is
   then added to its index.  If the resulting index is now negative, it
   is clamped to 0.  This index is now used exactly as though it were
   supplied as the "position" argument.  If the anchor is not found, the
   call is rejected with an "anchorNotFound" error.

   If an "anchor" is specified, any position argument supplied by the
   client MUST be ignored.  If no "anchor" is supplied, any
   "anchorOffset" argument MUST be ignored.

   A client can use "anchor" instead of "position" to find the index of
   an id within a large set of results.

   The response has the following arguments:

   o  accountId: "Id"

      The id of the account used for the call.

   o  queryState: "String"

      A string encoding the current state of the query on the server.
      This string MUST change if the results of the query (i.e., the
      matching ids and their sort order) have changed.  The queryState
      string MAY change if something has changed on the server, which
      means the results may have changed but the server doesn't know for
      sure.

      The queryState string only represents the ordered list of ids that
      match the particular query (including its sort/filter).  There is
      no requirement for it to change if a property on an object
      matching the query changes but the query results are unaffected
      (indeed, it is more efficient if the queryState string does not
      change in this case).  The queryState string only has meaning when
      compared to future responses to a query with the same type/sort/
      filter or when used with /queryChanges to fetch changes.

      Should a client receive back a response with a different
      queryState string to a previous call, it MUST either throw away
      the currently cached query and fetch it again (note, this does not
      require fetching the records again, just the list of ids) or call
      "Foo/queryChanges" to get the difference.








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   o  canCalculateChanges: "Boolean"

      This is true if the server supports calling "Foo/queryChanges"
      with these "filter"/"sort" parameters.  Note, this does not
      guarantee that the "Foo/queryChanges" call will succeed, as it may
      only be possible for a limited time afterwards due to server
      internal implementation details.

   o  position: "UnsignedInt"

      The zero-based index of the first result in the "ids" array within
      the complete list of query results.

   o  ids: "Id[]"

      The list of ids for each Foo in the query results, starting at the
      index given by the "position" argument of this response and
      continuing until it hits the end of the results or reaches the
      "limit" number of ids.  If "position" is >= "total", this MUST be
      the empty list.

   o  total: "UnsignedInt" (only if requested)

      The total number of Foos in the results (given the "filter").
      This argument MUST be omitted if the "calculateTotal" request
      argument is not true.

   o  limit: "UnsignedInt" (if set by the server)

      The limit enforced by the server on the maximum number of results
      to return.  This is only returned if the server set a limit or
      used a different limit than that given in the request.

   The following additional errors may be returned instead of the "Foo/
   query" response:

   "anchorNotFound": An anchor argument was supplied, but it cannot be
   found in the results of the query.

   "unsupportedSort": The "sort" is syntactically valid, but it includes
   a property the server does not support sorting on or a collation
   method it does not recognise.

   "unsupportedFilter": The "filter" is syntactically valid, but the
   server cannot process it.  If the filter was the result of a user's
   search input, the client SHOULD suggest that the user simplify their
   search.




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5.6.  /queryChanges

   The "Foo/queryChanges" method allows a client to efficiently update
   the state of a cached query to match the new state on the server.  It
   takes the following arguments:

   o  accountId: "Id"

      The id of the account to use.

   o  filter: "FilterOperator|FilterCondition|null"

      The filter argument that was used with "Foo/query".

   o  sort: "Comparator[]|null"

      The sort argument that was used with "Foo/query".

   o  sinceQueryState: "String"

      The current state of the query in the client.  This is the string
      that was returned as the "queryState" argument in the "Foo/query"
      response with the same sort/filter.  The server will return the
      changes made to the query since this state.

   o  maxChanges: "UnsignedInt|null"

      The maximum number of changes to return in the response.  See
      error descriptions below for more details.

   o  upToId: "Id|null"

      The last (highest-index) id the client currently has cached from
      the query results.  When there are a large number of results, in a
      common case, the client may have only downloaded and cached a
      small subset from the beginning of the results.  If the sort and
      filter are both only on immutable properties, this allows the
      server to omit changes after this point in the results, which can
      significantly increase efficiency.  If they are not immutable,
      this argument is ignored.

   o  calculateTotal: "Boolean" (default: false)

      Does the client wish to know the total number of results now in
      the query?  This may be slow and expensive for servers to
      calculate, particularly with complex filters, so clients should
      take care to only request the total when needed.




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   The response has the following arguments:

   o  accountId: "Id"

      The id of the account used for the call.

   o  oldQueryState: "String"

      This is the "sinceQueryState" argument echoed back; that is, the
      state from which the server is returning changes.

   o  newQueryState: "String"

      This is the state the query will be in after applying the set of
      changes to the old state.

   o  total: "UnsignedInt" (only if requested)

      The total number of Foos in the results (given the "filter").
      This argument MUST be omitted if the "calculateTotal" request
      argument is not true.

   o  removed: "Id[]"

      The "id" for every Foo that was in the query results in the old
      state and that is not in the results in the new state.

      If the server cannot calculate this exactly, the server MAY return
      the ids of extra Foos in addition that may have been in the old
      results but are not in the new results.

      If the sort and filter are both only on immutable properties and
      an "upToId" is supplied and exists in the results, any ids that
      were removed but have a higher index than "upToId" SHOULD be
      omitted.

      If the "filter" or "sort" includes a mutable property, the server
      MUST include all Foos in the current results for which this
      property may have changed.  The position of these may have moved
      in the results, so they must be reinserted by the client to ensure
      its query cache is correct.










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   o  added: "AddedItem[]"

      The id and index in the query results (in the new state) for every
      Foo that has been added to the results since the old state AND
      every Foo in the current results that was included in the
      "removed" array (due to a filter or sort based upon a mutable
      property).

      If the sort and filter are both only on immutable properties and
      an "upToId" is supplied and exists in the results, any ids that
      were added but have a higher index than "upToId" SHOULD be
      omitted.

      The array MUST be sorted in order of index, with the lowest index
      first.

      An *AddedItem* object has the following properties:

      *  id: "Id"

      *  index: "UnsignedInt"

   The result of this is that if the client has a cached sparse array of
   Foo ids corresponding to the results in the old state, then:

   fooIds = [ "id1", "id2", null, null, "id3", "id4", null, null, null ]

   If it *splices out* all ids in the removed array that it has in its
   cached results, then:

      removed = [ "id2", "id31", ... ];
      fooIds => [ "id1", null, null, "id3", "id4", null, null, null ]

   and *splices in* (one by one in order, starting with the lowest
   index) all of the ids in the added array:

  added = [{ id: "id5", index: 0, ... }];
  fooIds => [ "id5", "id1", null, null, "id3", "id4", null, null, null ]

   and *truncates* or *extends* to the new total length, then the
   results will now be in the new state.

   Note: splicing in adds the item at the given index, incrementing the
   index of all items previously at that or a higher index.  Splicing
   out is the inverse, removing the item and decrementing the index of
   every item after it in the array.





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   The following additional errors may be returned instead of the "Foo/
   queryChanges" response:

   "tooManyChanges": There are more changes than the client's
   "maxChanges" argument.  Each item in the removed or added array is
   considered to be one change.  The client may retry with higher max
   changes or invalidate its cache of the query results.

   "cannotCalculateChanges": The server cannot calculate the changes
   from the queryState string given by the client, usually due to the
   client's state being too old.  The client MUST invalidate its cache
   of the query results.

5.7.  Examples

   Suppose we have a type *Todo* with the following properties:

   o  id: "Id" (immutable; server-set)

      The id of the object.

   o  title: "String"

      A brief summary of what is to be done.

   o  keywords: "String[Boolean]" (default: {})

      A set of keywords that apply to the Todo.  The set is represented
      as an object, with the keys being the "keywords".  The value for
      each key in the object MUST be true.  (This format allows you to
      update an individual key using patch syntax rather than having to
      update the whole set of keywords as one, which a "String[]"
      representation would require.)

   o  neuralNetworkTimeEstimation: "Number" (server-set)

      The title and keywords are fed into the server's state-of-the-art
      neural network to get an estimation of how long this Todo will
      take, in seconds.

   o  subTodoIds: "Id[]|null"

      The ids of a list of other Todos to complete as part of this Todo.

   Suppose also that all the standard methods are defined for this type
   and the FilterCondition object supports a "hasKeyword" property to
   match Todos with the given keyword.




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   A client might want to display the list of Todos with either a
   "music" keyword or a "video" keyword, so it makes the following
   method call:

                   [[ "Todo/query", {
                     "accountId": "x",
                     "filter": {
                       "operator": "OR",
                       "conditions": [
                         { "hasKeyword": "music" },
                         { "hasKeyword": "video" }
                       ]
                     },
                     "sort": [{ "property": "title" }],
                     "position": 0,
                     "limit": 10
                   }, "0" ],
                   [ "Todo/get", {
                     "accountId": "x",
                     "#ids": {
                       "resultOf": "0",
                       "name": "Todo/query",
                       "path": "/ids"
                     }
                   }, "1" ]]


























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   This would query the server for the set of Todos with a keyword of
   either "music" or "video", sorted by title, and limited to the first
   10 results.  It fetches the full object for each of these Todos using
   back-references to reference the result of the query.  The response
   might look something like:

       [[ "Todo/query", {
         "accountId": "x",
         "queryState": "y13213",
         "canCalculateChanges": true,
         "position": 0,
         "ids": [ "a", "b", "c", "d", "e", "f", "g", "h", "i", "j" ]
       }, "0" ],
       [ "Todo/get", {
         "accountId": "x",
         "state": "10324",
         "list": [{
           "id": "a",
           "title": "Practise Piano",
           "keywords": {
             "music": true,
             "beethoven": true,
             "mozart": true,
             "liszt": true,
             "rachmaninov": true
           },
           "neuralNetworkTimeEstimation": 3600
         }, {
           "id": "b",
           "title": "Watch Daft Punk music video",
           "keywords": {
             "music": true,
             "video": true,
             "trance": true
           },
           "neuralNetworkTimeEstimation": 18000
         },
         ...
         ]
       }, "1" ]]











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   Now, suppose the user adds a keyword "chopin" and removes the keyword
   "mozart" from the "Practise Piano" task.  The client may send the
   whole object to the server, as this is a valid PatchObject:

                 [[ "Todo/set", {
                   "accountId": "x",
                   "ifInState": "10324",
                   "update": {
                     "a": {
                       "id": "a",
                       "title": "Practise Piano",
                       "keywords": {
                         "music": true,
                         "beethoven": true,
                         "chopin": true,
                         "liszt": true,
                         "rachmaninov": true
                       },
                       "neuralNetworkTimeEstimation": 360
                     }
                   }
                 }, "0" ]]

   or it may send a minimal patch:

                      [[ "Todo/set", {
                        "accountId": "x",
                        "ifInState": "10324",
                        "update": {
                          "a": {
                            "keywords/chopin": true,
                            "keywords/mozart": null
                          }
                        }
                      }, "0" ]]
















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   The effect is exactly the same on the server in either case, and
   presuming the server is still in state "10324", it will probably
   return success:

                 [[ "Todo/set", {
                   "accountId": "x",
                   "oldState": "10324",
                   "newState": "10329",
                   "updated": {
                     "a": {
                       "neuralNetworkTimeEstimation": 5400
                     }
                   }
                 }, "0" ]]

   The server changed the "neuralNetworkTimeEstimation" property on the
   object as part of this change; as this changed in a way *not*
   explicitly requested by the PatchObject sent to the server, it is
   returned with the "updated" confirmation.

   Let us now add a sub-Todo to our new "Practise Piano" Todo.  In this
   example, we can see the use of a reference to a creation id to allow
   us to set a foreign key reference to a record created in the same
   request:

                   [[ "Todo/set", {
                     "accountId": "x",
                     "create": {
                       "k15": {
                         "title": "Warm up with scales"
                       }
                     },
                     "update": {
                       "a": {
                         "subTodoIds": [ "#k15" ]
                       }
                     }
                   }, "0" ]]













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   Now, suppose another user deleted the "Listen to Daft Punk" Todo.
   The first user will receive a push notification (see Section 7) with
   the changed state string for the "Todo" type.  Since the new string
   does not match its current state, it knows it needs to check for
   updates.  It may make a request like:

                   [[ "Todo/changes", {
                     "accountId": "x",
                     "sinceState": "10324",
                     "maxChanges": 50
                   }, "0" ],
                   [ "Todo/queryChanges", {
                     "accountId": "x",
                     "filter": {
                       "operator": "OR",
                       "conditions": [
                         { "hasKeyword": "music" },
                         { "hasKeyword": "video" }
                       ]
                     },
                     "sort": [{ "property": "title" }],
                     "sinceQueryState": "y13213",
                     "maxChanges": 50
                   }, "1" ]]

   and receive in response:

                       [[ "Todo/changes", {
                         "accountId": "x",
                         "oldState": "10324",
                         "newState": "871903",
                         "hasMoreChanges": false,
                         "created": [],
                         "updated": [],
                         "destroyed": ["b"]
                       }, "0" ],
                       [ "Todo/queryChanges", {
                         "accountId": "x",
                         "oldQueryState": "y13213",
                         "newQueryState": "y13218",
                         "removed": ["b"],
                         "added": null
                       }, "1" ]]








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   Suppose the user has access to another account "y", for example, a
   team account shared between multiple users.  To move an existing Todo
   from account "x", the client would call:

                    [[ "Todo/copy", {
                      "fromAccountId": "x",
                      "accountId": "y",
                      "create": {
                        "k5122": {
                          "id": "a"
                        }
                      },
                      "onSuccessDestroyOriginal": true
                    }, "0" ]]

   The server successfully copies the Todo to a new account (where it
   receives a new id) and deletes the original.  Due to the implicit
   call to "Todo/set", there are two responses to the single method
   call, both with the same method call id:

                       [[ "Todo/copy", {
                         "fromAccountId": "x",
                         "accountId": "y",
                         "created": {
                           "k5122": {
                             "id": "DAf97"
                           }
                         },
                         "oldState": "c1d64ecb038c",
                         "newState": "33844835152b"
                       }, "0" ],
                       [ "Todo/set", {
                         "accountId": "x",
                         "oldState": "871903",
                         "newState": "871909",
                         "destroyed": [ "a" ],
                         ...
                       }, "0" ]]













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5.8.  Proxy Considerations

   JMAP has been designed to allow an API endpoint to easily proxy
   through to one or more JMAP servers.  This may be useful for load
   balancing, augmenting capabilities, or presenting a single endpoint
   to accounts hosted on different JMAP servers (splitting the request
   based on each method's "accountId" argument).  The proxy need only
   understand the general structure of a JMAP Request object; it does
   not need to know anything specifically about the methods and
   arguments it will pass through to other servers.

   If splitting up the methods in a request to call them on different
   backend servers, the proxy must do two things to ensure back-
   references and creation-id references resolve the same as if the
   entire request were processed on a single server:

   1.  It must pass a "createdIds" property with each subrequest.  If
       this is not given by the client, an empty object should be used
       for the first subrequest.  The "createdIds" property of each
       subresponse should be passed on in the next subrequest.

   2.  It must resolve back-references to previous method results that
       were processed on a different server.  This is a relatively
       simple syntactic substitution, described in Section 3.7.

   When splitting a request based on accountId, proxy implementors do
   need to be aware of "/copy" methods that copy between accounts.  If
   the accounts are on different servers, the proxy will have to
   implement this functionality directly.

6.  Binary Data

   Binary data is referenced by a *blobId* in JMAP and uploaded/
   downloaded separately to the core API.  The blobId solely represents
   the raw bytes of data, not any associated metadata such as a file
   name or content type.  Such metadata is stored alongside the blobId
   in the object referencing it.  The data represented by a blobId is
   immutable.

   Any blobId that exists within an account may be used when creating/
   updating another object in that account.  For example, an Email type
   may have a blobId that represents the object in Internet Message
   Format [RFC5322].  A client could create a new Email object with an
   attachment and use this blobId, in effect attaching the old message
   to the new one.  Similarly, it could attach any existing attachment
   of an old message without having to download and upload it again.





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   When the client uses a blobId in a create/update, the server MAY
   assign a new blobId to refer to the same binary data within the new/
   updated object.  If it does so, it MUST return any properties that
   contain a changed blobId in the created/updated response, so the
   client gets the new ids.

   A blob that is not referenced by a JMAP object (e.g., as a message
   attachment) MAY be deleted by the server to free up resources.
   Uploads (see below) are initially unreferenced blobs.  To ensure
   interoperability:

   o  The server SHOULD use a separate quota for unreferenced blobs to
      the account's usual quota.  In the case of shared accounts, this
      quota SHOULD be separate per user.

   o  This quota SHOULD be at least the maximum total size that a single
      object can reference on this server.  For example, if supporting
      JMAP Mail, this should be at least the maximum total attachments
      size for a message.

   o  When an upload would take the user over quota, the server MUST
      delete unreferenced blobs in date order, oldest first, until there
      is room for the new blob.

   o  Except where quota restrictions force early deletion, an
      unreferenced blob MUST NOT be deleted for at least 1 hour from the
      time of upload; if reuploaded, the same blobId MAY be returned,
      but this SHOULD reset the expiry time.

   o  A blob MUST NOT be deleted during the method call that removed the
      last reference, so that a client can issue a create and a destroy
      that both reference the blob within the same method call.

6.1.  Uploading Binary Data

   There is a single endpoint that handles all file uploads for an
   account, regardless of what they are to be used for.  The Session
   object (see Section 2) has an "uploadUrl" property in URI Template
   (level 1) format [RFC6570], which MUST contain a variable called
   "accountId".  The client may use this template in combination with an
   "accountId" to get the URL of the file upload resource.

   To upload a file, the client submits an authenticated POST request to
   the file upload resource.







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   A successful request MUST return a single JSON object with the
   following properties as the response:

   o  accountId: "Id"

      The id of the account used for the call.

   o  blobId: "Id"

      The id representing the binary data uploaded.  The data for this
      id is immutable.  The id *only* refers to the binary data, not any
      metadata.

   o  type: "String"

      The media type of the file (as specified in [RFC6838],
      Section 4.2) as set in the Content-Type header of the upload HTTP
      request.

   o  size: "UnsignedInt"

      The size of the file in octets.

   If identical binary content to an existing blob in the account is
   uploaded, the existing blobId MAY be returned.

   Clients should use the blobId returned in a timely manner.  Under
   rare circumstances, the server may have deleted the blob before the
   client uses it; the client should keep a reference to the local file
   so it can upload it again in such a situation.

   When an HTTP error response is returned to the client, the server
   SHOULD return a JSON "problem details" object as the response body,
   as per [RFC7807].

   As access controls are often determined by the object holding the
   reference to a blob, unreferenced blobs MUST only be accessible to
   the uploader, even in shared accounts.

6.2.  Downloading Binary Data

   The Session object (see Section 2) has a "downloadUrl" property,
   which is in URI Template (level 1) format [RFC6570].  The URL MUST
   contain variables called "accountId", "blobId", "type", and "name".







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   To download a file, the client makes an authenticated GET request to
   the download URL with the appropriate variables substituted in:

   o  "accountId": The id of the account to which the record with the
      blobId belongs.

   o  "blobId": The blobId representing the data of the file to
      download.

   o  "type": The type for the server to set in the "Content-Type"
      header of the response; the blobId only represents the binary data
      and does not have a content-type innately associated with it.

   o  "name": The name for the file; the server MUST return this as the
      filename if it sets a "Content-Disposition" header.

   As the data for a particular blobId is immutable, and thus the
   response in the generated download URL is too, implementors are
   recommended to set long cache times and use the "immutable" Cache-
   Control extension [RFC8246] for successful responses, for example,
   "Cache-Control: private, immutable, max-age=31536000".

   When an HTTP error response is returned to the client, the server
   SHOULD return a JSON "problem details" object as the response body,
   as per [RFC7807].

6.3.  Blob/copy

   Binary data may be copied *between* two different accounts using the
   "Blob/copy" method rather than having to download and then reupload
   on the client.

   The "Blob/copy" method takes the following arguments:

   o  fromAccountId: "Id"

      The id of the account to copy blobs from.

   o  accountId: "Id"

      The id of the account to copy blobs to.

   o  blobIds: "Id[]"

      A list of ids of blobs to copy to the other account.






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   The response has the following arguments:

   o  fromAccountId: "Id"

      The id of the account blobs were copied from.

   o  accountId: "Id"

      The id of the account blobs were copied to.

   o  copied: "Id[Id]|null"

      A map of the blobId in the fromAccount to the id for the blob in
      the account it was copied to, or null if none were successfully
      copied.

   o  notCopied: "Id[SetError]|null"

      A map of blobId to a SetError object for each blob that failed to
      be copied, or null if none.

   The SetError may be any of the standard set errors that may be
   returned for a create, as defined in Section 5.3.  In addition, the
   "notFound" SetError error may be returned if the blobId to be copied
   cannot be found.

   The following additional method-level error may be returned instead
   of the "Blob/copy" response:

   "fromAccountNotFound": The "fromAccountId" included with the request
   does not correspond to a valid account.

7.  Push

   Push notifications allow clients to efficiently update (almost)
   instantly to stay in sync with data changes on the server.  The
   general model for push is simple and sends minimal data over the push
   channel: just enough for the client to know whether it needs to
   resync.  The format allows multiple changes to be coalesced into a
   single push update and the frequency of pushes to be rate limited by
   the server.  It doesn't matter if some push events are dropped before
   they reach the client; the next time it gets/sets any records of a
   changed type, it will discover the data has changed and still sync
   all changes.







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   There are two different mechanisms by which a client can receive push
   notifications, to allow for the different environments in which a
   client may exist.  An event source resource (see Section 7.3) allows
   clients that can hold transport connections open to receive push
   notifications directly from the JMAP server.  This is simple and
   avoids third parties, but it is often not feasible on constrained
   platforms such as mobile devices.  Alternatively, clients can make
   use of any push service supported by their environment.  A URL for
   the push service is registered with the JMAP server (see
   Section 7.2); the server then POSTs each notification to that URL.
   The push service is then responsible for routing these to the client.

7.1.  The StateChange Object

   When something changes on the server, the server pushes a StateChange
   object to the client.  A *StateChange* object has the following
   properties:

   o  @type: "String"

      This MUST be the string "StateChange".

   o  changed: "Id[TypeState]"

      A map of an "account id" to an object encoding the state of data
      types that have changed for that account since the last
      StateChange object was pushed, for each of the accounts to which
      the user has access and for which something has changed.

      A *TypeState* object is a map.  The keys are the type name "Foo"
      (e.g., "Mailbox" or "Email"), and the value is the "state"
      property that would currently be returned by a call to "Foo/get".

      The client can compare the new state strings with its current
      values to see whether it has the current data for these types.  If
      not, the changes can then be efficiently fetched in a single
      standard API request (using the /changes type methods).














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7.1.1.  Example

   In this example, the server has amalgamated a few changes together
   across two different accounts the user has access to, before pushing
   the following StateChange object to the client:

                  {
                    "@type": "StateChange",
                    "changed": {
                      "a3123": {
                        "Email": "d35ecb040aab",
                        "EmailDelivery": "428d565f2440",
                        "CalendarEvent": "87accfac587a"
                      },
                      "a43461d": {
                        "Mailbox": "0af7a512ce70",
                        "CalendarEvent": "7a4297cecd76"
                      }
                    }
                  }

   The client can compare the state strings with its current state for
   the Email, CalendarEvent, etc., object types in the appropriate
   accounts to see if it needs to fetch changes.

   If the client is itself making changes, it may receive a StateChange
   object while the /set API call is in flight.  It can wait until the
   call completes and then compare if the new state string after the
   /set is the same as was pushed in the StateChange object; if so, and
   the old state of the /set response matches the client's previous
   state, it does not need to waste a request asking for changes it
   already knows.

7.2.  PushSubscription

   Clients may create a PushSubscription to register a URL with the JMAP
   server.  The JMAP server will then make an HTTP POST request to this
   URL for each push notification it wishes to send to the client.

   As a push subscription causes the JMAP server to make a number of
   requests to a previously unknown endpoint, it can be used as a vector
   for launching a denial-of-service attack.  To prevent this, when a
   subscription is created, the JMAP server immediately sends a
   PushVerification object to that URL (see Section 7.2.2).  The JMAP
   server MUST NOT make any further requests to the URL until the client
   receives the push and updates the subscription with the correct
   verification code.




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   A *PushSubscription* object has the following properties:

   o  id: "Id" (immutable; server-set)

      The id of the push subscription.

   o  deviceClientId: "String" (immutable)

      An id that uniquely identifies the client + device it is running
      on.  The purpose of this is to allow clients to identify which
      PushSubscription objects they created even if they lose their
      local state, so they can revoke or update them.  This string MUST
      be different on different devices and be different from apps from
      other vendors.  It SHOULD be easy to regenerate and not depend on
      persisted state.  It is RECOMMENDED to use a secure hash of a
      string that contains:

      1.  A unique identifier associated with the device where the JMAP
          client is running, normally supplied by the device's operating
          system.

      2.  A custom vendor/app id, including a domain controlled by the
          vendor of the JMAP client.

      To protect the privacy of the user, the deviceClientId id MUST NOT
      contain an unobfuscated device id.

   o  url: "String" (immutable)

      An absolute URL where the JMAP server will POST the data for the
      push message.  This MUST begin with "https://".

   o  keys: "Object|null" (immutable)

      Client-generated encryption keys.  If supplied, the server MUST
      use them as specified in [RFC8291] to encrypt all data sent to the
      push subscription.  The object MUST have the following properties:

      *  p256dh: "String"

         The P-256 Elliptic Curve Diffie-Hellman (ECDH) public key as
         described in [RFC8291], encoded in URL-safe base64
         representation as defined in [RFC4648].

      *  auth: "String"

         The authentication secret as described in [RFC8291], encoded in
         URL-safe base64 representation as defined in [RFC4648].



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   o  verificationCode: "String|null"

      This MUST be null (or omitted) when the subscription is created.
      The JMAP server then generates a verification code and sends it in
      a push message, and the client updates the PushSubscription object
      with the code; see Section 7.2.2 for details.

   o  expires: "UTCDate|null"

      The time this push subscription expires.  If specified, the JMAP
      server MUST NOT make further requests to this resource after this
      time.  It MAY automatically destroy the push subscription at or
      after this time.

      The server MAY choose to set an expiry if none is given by the
      client or modify the expiry time given by the client to a shorter
      duration.

   o  types: "String[]|null"

      A list of types the client is interested in (using the same names
      as the keys in the TypeState object defined in the previous
      section).  A StateChange notification will only be sent if the
      data for one of these types changes.  Other types are omitted from
      the TypeState object.  If null, changes will be pushed for all
      types.

   The POST request MUST have a content type of "application/json" and
   contain the UTF-8 JSON-encoded object as the body.  The request MUST
   have a "TTL" header and MAY have "Urgency" and/or "Topic" headers, as
   specified in Section 5 of [RFC8030].  The JMAP server is expected to
   understand and handle HTTP status responses in a reasonable manner.
   A "429" (Too Many Requests) response MUST cause the JMAP server to
   reduce the frequency of pushes; the JMAP push structure allows
   multiple changes to be coalesced into a single minimal StateChange
   object.  See the security considerations in Section 8.6 for a
   discussion of the risks in connecting to unknown servers.

   The JMAP server acts as an application server as defined in
   [RFC8030].  A client MAY use the rest of [RFC8030] in combination
   with its own push service to form a complete end-to-end solution, or
   it MAY rely on alternative mechanisms to ensure the delivery of the
   pushed data after it leaves the JMAP server.

   The push subscription is tied to the credentials used to authenticate
   the API request that created it.  Should these credentials expire or
   be revoked, the push subscription MUST be destroyed by the JMAP




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   server.  Only subscriptions created by these credentials are returned
   when the client fetches existing subscriptions.

   When these credentials have their own expiry (i.e., it is a session
   with a timeout), the server SHOULD NOT set or bound the expiry time
   for the push subscription given by the client but MUST expire it when
   the session expires.

   When these credentials are not time bounded (e.g., Basic
   authentication [RFC7617]), the server SHOULD set an expiry time for
   the push subscription if none is given and limit the expiry time if
   set too far in the future.  This maximum expiry time MUST be at least
   48 hours in the future and SHOULD be at least 7 days in the future.
   An app running on a mobile device may only be able to refresh the
   push subscription lifetime when it is in the foreground, so this
   gives a reasonable time frame to allow this to happen.

   In the case of separate access and refresh credentials, as in Oauth
   2.0 [RFC6749], the server SHOULD tie the push subscription to the
   validity of the refresh token rather than the access token and behave
   according to whether this is time-limited or not.

   When a push subscription is destroyed, the server MUST securely erase
   the URL and encryption keys from memory and storage as soon as
   possible.

7.2.1.  PushSubscription/get

   Standard /get method as described in Section 5.1, except it does
   *not* take or return an "accountId" argument, as push subscriptions
   are not tied to specific accounts.  It also does *not* return a
   "state" argument.  The "ids" argument may be null to fetch all at
   once.

   The server MUST only return push subscriptions that were created
   using the same authentication credentials as for this
   "PushSubscription/get" request.

   As the "url" and "keys" properties may contain data that is private
   to a particular device, the values for these properties MUST NOT be
   returned.  If the "properties" argument is null or omitted, the
   server MUST default to all properties excluding these two.  If one of
   them is explicitly requested, the method call MUST be rejected with a
   "forbidden" error.







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7.2.2.  PushSubscription/set

   Standard /set method as described in Section 5.3, except it does
   *not* take or return an "accountId" argument, as push subscriptions
   are not tied to specific accounts.  It also does *not* take an
   "ifInState" argument or return "oldState" or "newState" arguments.

   The "url" and "keys" properties are immutable; if the client wishes
   to change these, it must destroy the current push subscription and
   create a new one.

   When a PushSubscription is created, the server MUST immediately push
   a *PushVerification* object to the URL.  It has the following
   properties:

   o  @type: "String"

      This MUST be the string "PushVerification".

   o  pushSubscriptionId: "String"

      The id of the push subscription that was created.

   o  verificationCode: "String"

      The verification code to add to the push subscription.  This MUST
      contain sufficient entropy to avoid the client being able to guess
      the code via brute force.

   The client MUST update the push subscription with the correct
   verification code before the server makes any further requests to the
   subscription's URL.  Attempts to update the subscription with an
   invalid verification code MUST be rejected by the server with an
   "invalidProperties" SetError.

   The client may update the "expires" property to extend (or, less
   commonly, shorten) the lifetime of a push subscription.  The server
   MAY modify the proposed new expiry time to enforce server-defined
   limits.  Extending the lifetime does not require the subscription to
   be verified again.

   Clients SHOULD NOT update or destroy a push subscription that they
   did not create (i.e., has a "deviceClientId" that they do not
   recognise).







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7.2.3.  Example

   At "2018-07-06T02:14:29Z", a client with deviceClientId "a889-ffea-
   910" fetches the set of push subscriptions currently on the server,
   making an API request with:

                       [[ "PushSubscription/get", {
                         "ids": null
                       }, "0" ]]

   Which returns:

       [[ "PushSubscription/get", {
         "list": [{
             "id": "e50b2c1d-9553-41a3-b0a7-a7d26b599ee1",
             "deviceClientId": "b37ff8001ca0",
             "verificationCode": "b210ef734fe5f439c1ca386421359f7b",
             "expires": "2018-07-31T00:13:21Z",
             "types": [ "Todo" ]
         }, {
             "id": "f2d0aab5-e976-4e8b-ad4b-b380a5b987e4",
             "deviceClientId": "X8980fc",
             "verificationCode": "f3d4618a9ae15c8b7f5582533786d531",
             "expires": "2018-07-12T05:55:00Z",
             "types": [ "Mailbox", "Email", "EmailDelivery" ]
         }],
         "notFound": []
       }, "0" ]]

   Since neither of the returned push subscription objects have the
   client's deviceClientId, it knows it does not have a current push
   subscription active on the server.  So it creates one, sending this
   request:

[[ "PushSubscription/set", {
  "create": {
    "4f29": {
      "deviceClientId": "a889-ffea-910",
      "url": "https://example.com/push/?device=X8980fc&client=12c6d086",
      "types": null
    }
  }
}, "0" ]]








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   The server creates the push subscription but limits the expiry time
   to 7 days in the future, returning this response:

            [[ "PushSubscription/set", {
              "created": {
                "4f29": {
                  "id": "P43dcfa4-1dd4-41ef-9156-2c89b3b19c60",
                  "keys": null,
                  "expires": "2018-07-13T02:14:29Z"
                }
              }
            }, "0" ]]

   The server also immediately makes a POST request to
   "https://example.com/push/?device=X8980fc&client=12c6d086" with the
   data:

      {
        "@type": "PushVerification",
        "pushSubscriptionId": "P43dcfa4-1dd4-41ef-9156-2c89b3b19c60",
        "verificationCode": "da1f097b11ca17f06424e30bf02bfa67"
      }

   The client receives this and updates the subscription with the
   verification code (note there is a potential race condition here; the
   client MUST be able to handle receiving the push while the request
   creating the subscription is still in progress):

       [[ "PushSubscription/set", {
         "update": {
           "P43dcfa4-1dd4-41ef-9156-2c89b3b19c60": {
             "verificationCode": "da1f097b11ca17f06424e30bf02bfa67"
           }
         }
       }, "0" ]]

   The server confirms the update was successful and will now make
   requests to the registered URL when the state changes.













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   Two days later, the client updates the subscription to extend its
   lifetime, sending this request:

               [[ "PushSubscription/set", {
                 "update": {
                   "P43dcfa4-1dd4-41ef-9156-2c89b3b19c60": {
                     "expires": "2018-08-13T00:00:00Z"
                   }
                 }
               }, "0" ]]

   The server extends the expiry time, but only again to its maximum
   limit of 7 days in the future, returning this response:

               [[ "PushSubscription/set", {
                 "updated": {
                   "P43dcfa4-1dd4-41ef-9156-2c89b3b19c60": {
                     "expires": "2018-07-15T02:22:50Z"
                   }
                 }
               }, "0" ]]

7.3.  Event Source

   Clients that can hold transport connections open can connect directly
   to the JMAP server to receive push notifications via a "text/event-
   stream" resource, as described in [EventSource].  This is a long
   running HTTP request, where the server can push data to the client by
   appending data without ending the response.

   When a change occurs in the data on the server, it pushes an event
   called "state" to any connected clients, with the StateChange object
   as the data.

   The server SHOULD also send a new event id that encodes the entire
   server state visible to the user immediately after sending a "state"
   event.  When a new connection is made to the event-source endpoint, a
   client following the server-sent events specification will send a
   Last-Event-ID HTTP header field with the last id it saw, which the
   server can use to work out whether the client has missed some
   changes.  If so, it SHOULD send these changes immediately on
   connection.

   The Session object (see Section 2) has an "eventSourceUrl" property,
   which is in URI Template (level 1) format [RFC6570].  The URL MUST
   contain variables called "types", "closeafter", and "ping".





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   To connect to the resource, the client makes an authenticated GET
   request to the event-source URL with the appropriate variables
   substituted in:

   o  "types": This MUST be either:

      *  A comma-separated list of type names, e.g.,
         "Email,CalendarEvent".  The server MUST only push changes for
         the types in this list.

      *  The single character: "*".  Changes to all types are pushed.

   o  "closeafter": This MUST be one of the following values:

      *  "state": The server MUST end the HTTP response after pushing a
         state event.  This can be used by clients in environments where
         buffering proxies prevent the pushed data from arriving
         immediately, or indeed at all, when operating in the usual
         mode.

      *  "no": The connection is persisted by the server as a standard
         event-source resource.

   o  "ping": A positive integer value representing a length of time in
      seconds, e.g., "300".  If non-zero, the server MUST send an event
      called "ping" whenever this time elapses since the previous event
      was sent.  This MUST NOT set a new event id.  If the value is "0",
      the server MUST NOT send ping events.

      The server MAY modify a requested ping interval to be subject to a
      minimum and/or maximum value.  For interoperability, servers MUST
      NOT have a minimum allowed value higher than 30 or a maximum
      allowed value less than 300.

      The data for the ping event MUST be a JSON object containing an
      "interval" property, the value (type "UnsignedInt") being the
      interval in seconds the server is using to send pings (this may be
      different to the requested value if the server clamped it to be
      within a min/max value).

      Clients can monitor for the ping event to help determine when the
      closeafter mode may be required.

   A client MAY hold open multiple connections to the event-source
   resource, although it SHOULD try to use a single connection for
   efficiency.





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8.  Security Considerations

8.1.  Transport Confidentiality

   To ensure the confidentiality and integrity of data sent and received
   via JMAP, all requests MUST use TLS 1.2 [RFC5246] [RFC8446] or later,
   following the recommendations in [RFC7525].  Servers SHOULD support
   TLS 1.3 [RFC8446] or later.

   Clients MUST validate TLS certificate chains to protect against
   man-in-the-middle attacks [RFC5280].

8.2.  Authentication Scheme

   A number of HTTP authentication schemes have been standardised (see
   <https://www.iana.org/assignments/http-authschemes/>).  Servers
   should take care to assess the security characteristics of different
   schemes in relation to their needs when deciding what to implement.

   Use of the Basic authentication scheme is NOT RECOMMENDED.  Services
   that choose to use it are strongly recommended to require generation
   of a unique "app password" via some external mechanism for each
   client they wish to connect.  This allows connections from different
   devices to be differentiated by the server and access to be
   individually revoked.

8.3.  Service Autodiscovery

   Unless secured by something like DNSSEC, autodiscovery of server
   details using SRV DNS records is vulnerable to a DNS poisoning
   attack, which can lead to the client talking to an attacker's server
   instead of the real JMAP server.  The attacker may then intercept
   requests to execute man-in-the-middle attacks and, depending on the
   authentication scheme, steal credentials to generate its own
   requests.

   Clients that do not support SRV lookups are likely to try just using
   the "/.well-known/jmap" path directly against the domain of the
   username over HTTPS.  Servers SHOULD ensure this path resolves or
   redirects to the correct JMAP Session resource to allow this to work.
   If this is not feasible, servers MUST ensure this path cannot be
   controlled by an attacker, as again it may be used to steal
   credentials.








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8.4.  JSON Parsing

   The Security Considerations of [RFC8259] apply to the use of JSON as
   the data interchange format.

   As for any serialization format, parsers need to thoroughly check the
   syntax of the supplied data.  JSON uses opening and closing tags for
   several types and structures, and it is possible that the end of the
   supplied data will be reached when scanning for a matching closing
   tag; this is an error condition, and implementations need to stop
   scanning at the end of the supplied data.

   JSON also uses a string encoding with some escape sequences to encode
   special characters within a string.  Care is needed when processing
   these escape sequences to ensure that they are fully formed before
   the special processing is triggered, with special care taken when the
   escape sequences appear adjacent to other (non-escaped) special
   characters or adjacent to the end of data (as in the previous
   paragraph).

   If parsing JSON into a non-textual structured data format,
   implementations may need to allocate storage to hold JSON string
   elements.  Since JSON does not use explicit string lengths, the risk
   of denial of service due to resource exhaustion is small, but
   implementations may still wish to place limits on the size of
   allocations they are willing to make in any given context, to avoid
   untrusted data causing excessive memory allocation.

8.5.  Denial of Service

   A small request may result in a very large response and require
   considerable work on the server if resource limits are not enforced.
   JMAP provides mechanisms for advertising and enforcing a wide variety
   of limits for mitigating this threat, including limits on the number
   of objects fetched in a single method call, number of methods in a
   single request, number of concurrent requests, etc.

   JMAP servers MUST implement sensible limits to mitigate against
   resource exhaustion attacks.

8.6.  Connection to Unknown Push Server

   When a push subscription is registered, the application server will
   make POST requests to the given URL.  There are a number of security
   considerations that MUST be considered when implementing this.






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   The server MUST ensure the URL is externally resolvable to avoid
   server-side request forgery, where the server makes a request to a
   resource on its internal network.

   A malicious client may use the push subscription to attempt to flood
   a third party server with requests, creating a denial-of-service
   attack and masking the attacker's true identity.  There is no
   guarantee that the URL given to the JMAP server is actually a valid
   push server.  Upon creation of a push subscription, the JMAP server
   sends a PushVerification object to the URL and MUST NOT send any
   further requests until the client verifies it has received the
   initial push.  The verification code MUST contain sufficient entropy
   to prevent the client from being able to verify the subscription via
   brute force.

   The verification code does not guarantee the URL is a valid push
   server, only that the client is able to access the data submitted to
   it.  While the verification step significantly reduces the set of
   potential targets, there is still a risk that the server is unrelated
   to the client and being targeted for a denial-of-service attack.

   The server MUST limit the number of push subscriptions any one user
   may have to ensure the user cannot cause the server to send a large
   number of push notifications at once, which could again be used as
   part of a denial-of-service attack.  The rate of creation MUST also
   be limited to minimise the ability to abuse the verification request
   as an attack vector.

8.7.  Push Encryption

   When data changes, a small object is pushed with the new state
   strings for the types that have changed.  While the data here is
   minimal, a passive man-in-the-middle attacker may be able to gain
   useful information.  To ensure confidentiality and integrity, if the
   push is sent via a third party outside of the control of the client
   and JMAP server, the client MUST specify encryption keys when
   establishing the PushSubscription and ignore any push notification
   received that is not encrypted with those keys.

   The privacy and security considerations of [RFC8030] and [RFC8291]
   also apply to the use of the PushSubscription mechanism.

   As there is no crypto algorithm agility in Web Push Encryption
   [RFC8291], a new specification will be needed to provide this if new
   algorithms are required in the future.






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8.8.  Traffic Analysis

   While the data is encrypted, a passive observer with the ability to
   monitor network traffic may be able to glean information from the
   timing of API requests and push notifications.  For example, suppose
   an email or calendar invitation is sent from User A (hosted on Server
   X) to User B (hosted on Server Y).  If Server X hosts data for many
   users, a passive observer can see that the two servers connected but
   does not know who the data was for.  However, if a push notification
   is immediately sent to User B and the attacker can observe this as
   well, they may reasonably conclude that someone on Server X is
   connecting to User B.

9.  IANA Considerations

9.1.  Assignment of jmap Service Name

   IANA has assigned the 'jmap' service name in the "Service Name and
   Transport Protocol Port Number Registry" [RFC6335].

   Service Name: jmap

   Transport Protocol(s): tcp

   Assignee: IESG

   Contact: IETF Chair

   Description: JSON Meta Application Protocol

   Reference: RFC 8620

   Assignment Notes: This service name was previously assigned under the
   name "JSON Mail Access Protocol".  This has been de-assigned and
   re-assigned with the approval of the previous assignee.

9.2.  Registration of Well-Known URI Suffix for JMAP

   IANA has registered the following suffix in the "Well-Known URIs"
   registry for JMAP, as described in [RFC8615]:

   URI Suffix: jmap

   Change Controller: IETF

   Specification Document: RFC 8620, Section 2.2.





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9.3.  Registration of the jmap URN Sub-namespace

   IANA has registered the following URN sub-namespace in the "IETF URN
   Sub-namespace for Registered Protocol Parameter Identifiers" registry
   within the "Uniform Resource Name (URN) Namespace for IETF Use"
   registry as described in [RFC3553].

   Registered Parameter Identifier: jmap

   Reference: RFC 8620, Section 9.4

   IANA Registry Reference: http://www.iana.org/assignments/jmap

9.4.  Creation of "JMAP Capabilities" Registry

   IANA has created the "JMAP Capabilities" registry as described in
   Section 2.  JMAP capabilities are advertised in the "capabilities"
   property of the JMAP Session resource.  They are used to extend the
   functionality of a JMAP server.  A capability is referenced by a URI.
   The JMAP capability URI can be a URN starting with
   "urn:ietf:params:jmap:" plus a unique suffix that is the index value
   in the jmap URN sub-namespace.  Registration of a JMAP capability
   with another form of URI has no impact on the jmap URN sub-namespace.

   This registry follows the expert review process unless the "intended
   use" field is "common" or "placeholder", in which case registration
   follows the specification required process.

   A JMAP capability registration can have an intended use of "common",
   "placeholder", "limited", or "obsolete".  IANA will list common-use
   registrations prominently and separately from those with other
   intended use values.

   The JMAP capability registration procedure is not a formal standards
   process but rather an administrative procedure intended to allow
   community comment and sanity checking without excessive time delay.

   A "placeholder" registration reserves part of the jmap URN namespace
   for another purpose but is typically not included in the
   "capabilities" property of the JMAP Session resource.

9.4.1.  Preliminary Community Review

   Notice of a potential JMAP common-use registration SHOULD be sent to
   the JMAP mailing list <jmap@ietf.org> for review.  This mailing list
   is appropriate to solicit community feedback on a proposed JMAP





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   capability.  Registrations that are not intended for common use MAY
   be sent to the list for review as well; doing so is entirely
   OPTIONAL, but is encouraged.

   The intent of the public posting to this list is to solicit comments
   and feedback on the choice of the capability name, the unambiguity of
   the specification document, and a review of any interoperability or
   security considerations.  The submitter may submit a revised
   registration proposal or abandon the registration completely at any
   time.

9.4.2.  Submit Request to IANA

   Registration requests can be sent to <iana@iana.org>.

9.4.3.  Designated Expert Review

   For a limited-use registration, the primary concern of the designated
   expert (DE) is preventing name collisions and encouraging the
   submitter to document security and privacy considerations; a
   published specification is not required.  For a common-use
   registration, the DE is expected to confirm that suitable
   documentation, as described in Section 4.6 of [RFC8126], is
   available.  The DE should also verify that the capability does not
   conflict with work that is active or already published within the
   IETF.

   Before a period of 30 days has passed, the DE will either approve or
   deny the registration request and publish a notice of the decision to
   the JMAP WG mailing list or its successor, as well as inform IANA.  A
   denial notice must be justified by an explanation, and, in the cases
   where it is possible, concrete suggestions on how the request can be
   modified so as to become acceptable should be provided.

   If the DE does not respond within 30 days, the registrant may request
   the IESG take action to process the request in a timely manner.

9.4.4.  Change Procedures

   Once a JMAP capability has been published by the IANA, the change
   controller may request a change to its definition.  The same
   procedure that would be appropriate for the original registration
   request is used to process a change request.

   JMAP capability registrations may not be deleted; capabilities that
   are no longer believed appropriate for use can be declared obsolete
   by a change to their "intended use" field; such capabilities will be
   clearly marked in the lists published by the IANA.



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   Significant changes to a capability's definition should be requested
   only when there are serious omissions or errors in the published
   specification.  When review is required, a change request may be
   denied if it renders entities that were valid under the previous
   definition invalid under the new definition.

   The owner of a JMAP capability may pass responsibility to another
   person or agency by informing the IANA; this can be done without
   discussion or review.

   The IESG may reassign responsibility for a JMAP capability.  The most
   common case of this will be to enable changes to be made to
   capabilities where the author of the registration has died, moved out
   of contact, or is otherwise unable to make changes that are important
   to the community.

9.4.5.  JMAP Capabilities Registry Template

   Capability name: (see capability property in Section 2)

   Specification document:

   Intended use: (one of common, limited, placeholder, or obsolete)

   Change controller: ("IETF" for Standards Track / BCP RFCs)

   Security and privacy considerations:

9.4.6.  Initial Registration for JMAP Core

   Capability Name: "urn:ietf:params:jmap:core"

   Specification document: RFC 8620, Section 2

   Intended use: common

   Change Controller: IETF

   Security and privacy considerations: RFC 8620, Section 8.












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9.4.7.  Registration for JMAP Error Placeholder in JMAP Capabilities
        Registry

   Capability Name: "urn:ietf:params:jmap:error:"

   Specification document: RFC 8620, Section 9.5

   Intended use: placeholder

   Change Controller: IETF

   Security and privacy considerations: RFC 8620, Section 8.

9.5.  Creation of "JMAP Error Codes" Registry

   IANA has created the "JMAP Error Codes" registry.  JMAP error codes
   appear in the "type" member of a JSON problem details object (as
   described in Section 3.6.1), the "type" member in a JMAP error object
   (as described in Section 3.6.2), or the "type" member of a JMAP
   method-specific error object (such as SetError in Section 5.3).  When
   used in a problem details object, the prefix
   "urn:ietf:params:jmap:error:" is always included; when used in JMAP
   objects, the prefix is always omitted.

   This registry follows the expert review process.  Preliminary
   community review for this registry follows the same procedures as the
   "JMAP Capabilities" registry, but it is optional.  The change
   procedures for this registry are the same as the change procedures
   for the "JMAP Capabilities" registry.

9.5.1.  Expert Review

   The designated expert should review the following aspects of the
   registration:

   1.  Verify the error code does not conflict with existing names.

   2.  Verify the error code follows the syntax limitations (does not
       require URI encoding).

   3.  Encourage the submitter to follow the naming convention of
       previously registered errors.

   4.  Encourage the submitter to describe client behaviours that are
       recommended in response to the error code.  These may distinguish
       the error code from other error codes.





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   5.  Encourage the submitter to describe when the server should issue
       the error as opposed to some other error code.

   6.  Encourage the submitter to note any security considerations
       associated with the error, if any (e.g., an error code that might
       disclose existence of data the authenticated user does not have
       permission to know about).

   Steps 3-6 are meant to promote a higher-quality registry.  However,
   the expert is encouraged to approve any registration that would not
   actively harm JMAP interoperability to make this a relatively
   lightweight process.

9.5.2.  JMAP Error Codes Registry Template

   JMAP Error Code:

   Intended use: (one of "common", "limited", "obsolete")

   Change Controller: ("IETF" for Standards Track / BCP RFCs)

   Reference: (Optional.  Only required if defined in an RFC.)

   Description:

9.5.3.  Initial Contents for the JMAP Error Codes Registry

   o  JMAP Error Code: accountNotFound
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: The accountId does not correspond to a valid account.

   o  JMAP Error Code: accountNotSupportedByMethod
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: The accountId given corresponds to a valid account,
      but the account does not support this method or data type.

   o  JMAP Error Code: accountReadOnly
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: This method modifies state, but the account is read-
      only (as returned on the corresponding Account object in the JMAP
      Session resource).




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   o  JMAP Error Code: anchorNotFound
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.5
      Description: An anchor argument was supplied, but it cannot be
      found in the results of the query.

   o  JMAP Error Code: alreadyExists
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.4
      Description: The server forbids duplicates, and the record already
      exists in the target account.  An existingId property of type Id
      MUST be included on the SetError object with the id of the
      existing record.

   o  JMAP Error Code: cannotCalculateChanges
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Sections 5.2 and 5.6
      Description: The server cannot calculate the changes from the
      state string given by the client.

   o  JMAP Error Code: forbidden
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Sections 3.6.2, 5.3, and 7.2.1
      Description: The action would violate an ACL or other permissions
      policy.

   o  JMAP Error Code: fromAccountNotFound
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Sections 5.4 and 6.3
      Description: The fromAccountId does not correspond to a valid
      account.

   o  JMAP Error Code: fromAccountNotSupportedByMethod
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.4
      Description: The fromAccountId given corresponds to a valid
      account, but the account does not support this data type.








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   o  JMAP Error Code: invalidArguments
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: One of the arguments is of the wrong type or
      otherwise invalid, or a required argument is missing.

   o  JMAP Error Code: invalidPatch
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: The PatchObject given to update the record was not a
      valid patch.

   o  JMAP Error Code: invalidProperties
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: The record given is invalid.

   o  JMAP Error Code: notFound
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: The id given cannot be found.

   o  JMAP Error Code: notJSON
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.1
      Description: The content type of the request was not application/
      json, or the request did not parse as I-JSON.

   o  JMAP Error Code: notRequest
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.1
      Description: The request parsed as JSON but did not match the type
      signature of the Request object.

   o  JMAP Error Code: overQuota
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: The create would exceed a server-defined limit on the
      number or total size of objects of this type.





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   o  JMAP Error Code: rateLimit
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: Too many objects of this type have been created
      recently, and a server-defined rate limit has been reached.  It
      may work if tried again later.

   o  JMAP Error Code: requestTooLarge
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Sections 5.1 and 5.3
      Description: The total number of actions exceeds the maximum
      number the server is willing to process in a single method call.

   o  JMAP Error Code: invalidResultReference
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: The method used a result reference for one of its
      arguments, but this failed to resolve.

   o  JMAP Error Code: serverFail
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: An unexpected or unknown error occurred during the
      processing of the call.  The method call made no changes to the
      server's state.

   o  JMAP Error Code: serverPartialFail
      Intended Use: Limited
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: Some, but not all, expected changes described by the
      method occurred.  The client MUST resynchronise impacted data to
      determine the server state.  Use of this error is strongly
      discouraged.

   o  JMAP Error Code: serverUnavailable
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: Some internal server resource was temporarily
      unavailable.  Attempting the same operation later (perhaps after a
      backoff with a random factor) may succeed.





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   o  JMAP Error Code: singleton
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: This is a singleton type, so you cannot create
      another one or destroy the existing one.

   o  JMAP Error Code: stateMismatch
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: An ifInState argument was supplied, and it does not
      match the current state.

   o  JMAP Error Code: tooLarge
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: The action would result in an object that exceeds a
      server-defined limit for the maximum size of a single object of
      this type.

   o  JMAP Error Code: tooManyChanges
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.6
      Description: There are more changes than the client's maxChanges
      argument.

   o  JMAP Error Code: unknownCapability
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.1
      Description: The client included a capability in the "using"
      property of the request that the server does not support.

   o  JMAP Error Code: unknownMethod
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 3.6.2
      Description: The server does not recognise this method name.

   o  JMAP Error Code: unsupportedFilter
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.5
      Description: The filter is syntactically valid, but the server
      cannot process it.



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   o  JMAP Error Code: unsupportedSort
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.5
      Description: The sort is syntactically valid but includes a
      property the server does not support sorting on or a collation
      method it does not recognise.

   o  JMAP Error Code: willDestroy
      Intended Use: Common
      Change Controller: IETF
      Reference: RFC 8620, Section 5.3
      Description: The client requested an object be both updated and
      destroyed in the same /set request, and the server has decided to
      therefore ignore the update.

10.  References

10.1.  Normative References

   [EventSource]
              Hickson, I., "Server-Sent Events", World Wide Web
              Consortium Recommendation REC-eventsource-20150203,
              February 2015, <https://www.w3.org/TR/eventsource/>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              DOI 10.17487/RFC2782, February 2000,
              <https://www.rfc-editor.org/info/rfc2782>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC3553]  Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
              IETF URN Sub-namespace for Registered Protocol
              Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
              2003, <https://www.rfc-editor.org/info/rfc3553>.




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   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <https://www.rfc-editor.org/info/rfc3629>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC4790]  Newman, C., Duerst, M., and A. Gulbrandsen, "Internet
              Application Protocol Collation Registry", RFC 4790,
              DOI 10.17487/RFC4790, March 2007,
              <https://www.rfc-editor.org/info/rfc4790>.

   [RFC5051]  Crispin, M., "i;unicode-casemap - Simple Unicode Collation
              Algorithm", RFC 5051, DOI 10.17487/RFC5051, October 2007,
              <https://www.rfc-editor.org/info/rfc5051>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <https://www.rfc-editor.org/info/rfc5322>.

   [RFC6186]  Daboo, C., "Use of SRV Records for Locating Email
              Submission/Access Services", RFC 6186,
              DOI 10.17487/RFC6186, March 2011,
              <https://www.rfc-editor.org/info/rfc6186>.

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <https://www.rfc-editor.org/info/rfc6335>.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570,
              DOI 10.17487/RFC6570, March 2012,
              <https://www.rfc-editor.org/info/rfc6570>.



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   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [RFC6764]  Daboo, C., "Locating Services for Calendaring Extensions
              to WebDAV (CalDAV) and vCard Extensions to WebDAV
              (CardDAV)", RFC 6764, DOI 10.17487/RFC6764, February 2013,
              <https://www.rfc-editor.org/info/rfc6764>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
              DOI 10.17487/RFC7493, March 2015,
              <https://www.rfc-editor.org/info/rfc7493>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC7617]  Reschke, J., "The 'Basic' HTTP Authentication Scheme",
              RFC 7617, DOI 10.17487/RFC7617, September 2015,
              <https://www.rfc-editor.org/info/rfc7617>.

   [RFC7807]  Nottingham, M. and E. Wilde, "Problem Details for HTTP
              APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
              <https://www.rfc-editor.org/info/rfc7807>.





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   [RFC8030]  Thomson, M., Damaggio, E., and B. Raymor, Ed., "Generic
              Event Delivery Using HTTP Push", RFC 8030,
              DOI 10.17487/RFC8030, December 2016,
              <https://www.rfc-editor.org/info/rfc8030>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8264]  Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
              Preparation, Enforcement, and Comparison of
              Internationalized Strings in Application Protocols",
              RFC 8264, DOI 10.17487/RFC8264, October 2017,
              <https://www.rfc-editor.org/info/rfc8264>.

   [RFC8291]  Thomson, M., "Message Encryption for Web Push", RFC 8291,
              DOI 10.17487/RFC8291, November 2017,
              <https://www.rfc-editor.org/info/rfc8291>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8615]  Nottingham, M., "Well-Known Uniform Resource Identifiers
              (URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
              <https://www.rfc-editor.org/info/rfc8615>.

10.2.  Informative References

   [RFC8246]  McManus, P., "HTTP Immutable Responses", RFC 8246,
              DOI 10.17487/RFC8246, September 2017,
              <https://www.rfc-editor.org/info/rfc8246>.









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RFC 8620                          JMAP                         July 2019


Authors' Addresses

   Neil Jenkins
   Fastmail
   PO Box 234, Collins St. West
   Melbourne, VIC  8007
   Australia

   Email: neilj@fastmailteam.com
   URI:   https://www.fastmail.com


   Chris Newman
   Oracle
   440 E. Huntington Dr., Suite 400
   Arcadia, CA  91006
   United States of America

   Email: chris.newman@oracle.com
































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