path: root/doc/rfc/rfc2372.txt

Network Working Group                                         K. Evans
Request for Comments: 2372                                    J. Klein
Category: Informational                               Tandem Computers
                                                               J. Lyon
                                                             Microsoft
                                                             July 1998


            Transaction Internet Protocol - Requirements and
                        Supplemental Information

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   This document describes the purpose (usage scenarios), and
   requirements for the Transaction Internet Protocol [1]. It is
   intended to help qualify the necessary features and functions of the
   protocol. It also provides supplemental information to aid
   understanding and facilitate implementation of the TIP protocol.

Table of Contents

   1.  Introduction                                               2
   2.  The Transaction Internet Protocol                          3
   3.  Scope                                                      4
   4.  Anticipated Usage of TIP                                   4
   5.  TIP Compliant Systems                                      4
   6.  Relationship to the X/Open DTP Model                       5
   7.  Example TIP Usage Scenario                                 5
   8.  TIP Transaction Recovery                                   9
   9.  TIP Transaction and Application Message Serialisation     10
   10. TIP Protocol and Local Actions                            10
   11. Security Considerations                                   11
   12. TIP Requirements                                          11
       References                                                14
       Authors' Addresses                                        15
       Comments                                                  15
   A.  An Example TIP Transaction Manager API                    16
       Full Copyright Statement                                  24



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1. Introduction

   Transactions are a very useful programming paradigm, greatly
   simplifying the writing of distributed applications. When
   transactions are employed, no matter how many distributed application
   components participate in a particular unit-of-work, the number of
   possible outcomes is reduced to only two; that is, either all of the
   work completed successfully, or none of it did (this characteristic
   is known as atomicity). Applications programming is therefore much
   less complex since the programmer does not have to deal with a
   multitude of possible failure scenarios. Typically, transaction
   semantics are provided by some underlying system infrastructure
   (usually in the form of products such as Transaction Processing
   Monitors, and/or Databases). This infrastructure deals with failures,
   and performs the necessary recovery actions to guarantee the property
   of atomicity. The use of transactions enables the development of
   reliable distributed applications which would otherwise be difficult,
   if not impossible.

   A key technology required to support distributed transactions is the
   two-phase commit protocol (2-pc). 2-pc protocols have been used in
   commercial Transaction Processing (TP) systems for many years, and
   are well understood (e.g. the LU6.2 2-pc (syncpoint) protocol was
   first implemented more than 12 years ago). Today a number of
   different 2-pc protocols are supported by a variety of TP monitor and
   database products. 2-pc is used between the components participating
   in a distributed unit-of-work (transaction) to ensure agreement by
   all parties regarding the outcome of that work (regardless of any
   failure).

   Today both standard and proprietary 2-pc protocols exist. These
   protocols typically employ a "one-pipe" model. That is, the
   transaction and application protocols are tightly-integrated,
   executing over the same communications channel. An application may
   use only the particular communications mechanism associated with the
   transaction protocol. The standard protocols (OSI TP, LU6.2) are
   complex, with a large footprint and extensive configuration and
   administration requirements. For these reasons they are not very
   widely deployed. The net of all this is restricted application
   flexibility and interoperability if transactions are to be used.
   Applications may wish to use a number of communications protocols for
   which there are no transactional variants (e.g. HTTP), and be
   deployed in very heterogeneous application environments.

   In summary, transactions greatly simplify the programming of
   distributed applications, and the 2-pc protocol is a key
   transactional technology. Current 2-pc protocols only offer
   transaction semantics to a limited set of applications, operating



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   within a special-purpose (complex, homogeneous) infrastructure, using
   a particular set of intercommunication protocols. The restrictions
   thus imposed by current 2-pc protocols limits the widespread use of
   the transaction paradigm, thereby inhibiting the development of new
   distributed business applications.

   (See [2] for more information re transactions, atomicity, and two-
   phase commit protocols in general.)

2. The Transaction Internet Protocol (TIP)

   TIP is a 2-pc protocol which is intended to provide ubiquitous
   distributed transaction support, in a heterogeneous (networked)
   environment. TIP removes the restrictions of current 2-pc protocols
   and enables the development of new distributed business applications.

   This goal is achieved primarily by satisfying two key requirements:

   1) Keep the protocol simple (yet functionally sufficient). If the
      protocol is complex it will not be widely deployed or quickly
      adopted. Simplicity also means suitability to a wide range of
      application environments.

   2) Enable the protocol to be used with any applications
      communications protocol (e.g. HTTP). This ensures heterogeneous
      environments can participate in distributed work.

   TIP does not reinvent the 2-pc protocol itself, the well-known
   presumed-abort 2-pc protocol is used as a basis. Rather the novelty
   and utility of TIP is in its separation from the application
   communications protocol (the two-pipe model).

      +-------------+ Application Communication +-------------+
      | Application |---------------------------| Application |
      |   Program   |         "Pipe 1"          |   Program   |
      +-------------+                           +-------------+
             |                                         |
             | TIP TM API                   TIP TM API |
             |                                         |
    +-----------------+   TIP 2-pc Protocol   +-----------------+
    | TIP Transaction |-----------------------| TIP Transaction |
    |     Manager     |       "Pipe 2"        |     Manager     |
    +-----------------+                       +-----------------+

                 Fig 1: The two-pipe nature of TIP






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3. Scope

   TIP does not describe how business transactions or electronic
   commerce are to be conducted on the internet, it specifies only the
   2-pc transaction protocol (which is an aid in the development of such
   applications). e.g. TIP does not provide a mechanism for non-
   repudiation. Such protocols might be a subject for subsequent IETF
   activity, once the requirements for general electronic commerce are
   better understood. TIP does not preclude the later definition of
   these protocols.

   TIP does not specify Application Programming Interfaces (note that an
   example TIP TM API is included in this document (Appendix A), as an
   aid to understanding).

4. Anticipated Usage of TIP

   As described above, transactions are a very useful tool in
   simplifying the programming of distributed applications. TIP is
   therefore targeted at any application that involves distributed work.
   Such applications may comprise components executing within a single
   system, across a corporate intranet, across the internet, or any
   other distributed system configuration. The application may be of
   "enterprise" class (requiring high-levels of performance and
   availability), or be less demanding. TIP is intended to be generally
   applicable, meeting the requirements of any application type which
   would benefit from the provision of transaction semantics.

5. TIP Compliant Systems

   There are two classes of TIP compliant Transaction Manager system:

   1) Client-only systems. Those which provide an application
      interface to demarcate TIP transactions, but which do not offer
      access to local recoverable resources. Such a lightweight
      implementation is useful for systems which host client
      applications only (e.g. desktop machines). Such client systems may
      be unreliable, and are not appropriate as transaction coordinators
      (their unavailability might cause resources on other transaction
      participant systems to remain locked and unavailable). These so-
      called "volatile client" systems therefore delegate the
      responsibility to coordinate the transaction (and recover from
      failures), to other "full" (server) TIP system implementations.
      For these lightweight systems, only the TIP IDENTIFY, BEGIN,
      COMMIT, and ABORT commands are needed; no transaction log is
      required.





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   2) Server systems. Those which offer the above support, plus TIP
      transaction coordination and recovery services. These systems may
      also provide access to recoverable resources (e.g. relational
      databases). Server systems support all TIP commands, and provide a
      recoverable transaction log.

   A TIP compliant Transaction Manager (TM), will also supply
   application programming interfaces to demarcate transactions (e.g.
   the X/Open TX interface [3]), plus commands to generate TIP URLs, to
   PUSH/PULL TIP transactions, and to set the current TIP transaction
   context. TIP support can be added to TMs with existing APIs and 2-pc
   protocols, and transactions may comprise both proprietary and TIP
   transaction branches (it is assumed existing TM implementations will
   provide "TIP gateway" facilities which will coordinate between TIP
   and other transaction protocols).

6. Relationship to the X/Open DTP Model

   The X/Open Distributed Transaction Processing (DTP) Model [4] defines
   four components: 1) Application Program (AP), 2) Transaction Manager
   (TM), 3) Resource Manager (RM), and 4) Communications Resource
   Manager (CRM). In this model, TIP defines a TM to TM interoperability
   protocol, which is independent of application communications (there
   is no such equivalent protocol specified by X/Open, where all
   transaction and application communication occurs between CRMs (the
   one-pipe model)).  Programmatic interfaces between the AP and TM/RM
   are unaffected by, and may be used with TIP. The TM to RM interaction
   is defined via the X/Open XA interface specification [5].  TIP is
   compatible with XA, and a TIP transaction may comprise applications
   accessing multiple RMs where the XA interface is being used to
   coordinate the RM transaction branches.

7. Example TIP Usage Scenario

   It is expected that a typical internet usage of TIP will involve
   applications using the agency model. In this model, the client node
   itself is not directly involved in the TIP protocol at all, and does
   not need the services of a local TIP TM. Instead, an agency (server)
   application handles the dialogue with the client, and is responsible
   for the coordination of the TIP transaction. The agency works with
   other service providers to deliver the service to the client. e.g. as
   a Travel Agency acts as an intermediate between airlines/hotels/etc
   and the customer. A big benefit of this model is that the agency is
   trusted by the service providers, and there are fewer such agencies
   (compared to user clients), so issues of security and performance are
   reduced.





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   Consider a Travel Agency example. A client running a web browser on a
   network PC accesses the Travel Agency web page. Via pages served up
   by the agency (which may in turn be constructed from pages provided
   by the airline and hotel servers), the client creates an itinerary
   involving flights and hotel choices. Finally, the client clicks the
   "make reservation" button. At this point the following sequence of
   events occurs (user-written application code is invoked by the
   various web servers, via any of the standard or proprietary
   techniques available (e.g. CGI)):

   1) The travel agency begins a local transaction, and gets a TIP URL
      for this transaction (both of these functions are performed using
      the API of the local TM. e.g. "tip_xid_to_url()" would return the
      TIP URL for the local transaction). The TIP URL contains the
      listening endpoint IP address of the local TM and the transaction
      identifier of the local transaction.

   2) The travel agency application sends a request to the airline
      server (via some protocol (e.g. HTTP)), requesting the
      "book_flight" service, passing the flights selected by the client,
      and the TIP URL (obtained in 1. above).

   3) The request is received by the airline server which invokes the
      book_flight application. This application retrieves the TIP URL
      from the input data, and passes this on a "tip_pull()" API request
      to its local TM. The tip_pull() function causes the following to
      occur:

      a. the local TM creates a local transaction (under which the
         work will be performed),

      b. if a TIP connection does not already exist to the superior
         (travel agency) TM (as identified via the IP address passed in
         the TIP URL), one is created and an IDENTIFY exchange occurs
         (if multiplexing is to be used on the connection, this is
         followed by a MULTIPLEX exchange),

      c. a PULL command is sent to the superior TM,

      d. in response to the PULL, the superior TM associates the
         subordinate (airline) TM with the transaction (by associating
         the connection with the transaction), and sends a PULLED
         response to the subordinate TM,

      e. the subordinate TM returns control to the book_flight
         application, which is now executing in the context of the newly
         created local transaction.




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   4) The book_flight application does its work (which may involve
      access to a recoverable resource manager (e.g. an RDBMS), in which
      case the local TM will associate the RM with the local transaction
      (via the XA interface or whatever)).

   5) The book_flight application returns to the travel agency
      application indicating success.

   6) Steps 2-5 are then repeated with the hotel server "book_room"
      application. At the conclusion of this, the superior TM has
      registered two subordinate TMs as participants in the transaction,
      there are TIP connections between the agency TM and the airline
      and hotel TMs, and there are inflight transactions at the airline
      and hotel servers. [Note that steps 2-5 and 6 could be performed
      in parallel.]

   7) The travel agency application issues a "commit transaction"
      request (using the API of the local TM). The local TM sends a
      PREPARE command on the TIP connections to the airline and hotel
      TMs (as these are registered as subordinate transaction
      participants).

   8) The TMs at the airline and hotel servers perform the
      necessary steps to prepare their local recoverable resources (e.g.
      by issuing xa_prepare() requests). If successful, the subordinate
      TMs change their TIP transaction state to Prepared, and log
      recovery information (e.g. local and superior transaction branch
      identifiers, and the IP address of the superior TM). The
      subordinate TMs then send PREPARED commands to the superior TM.

   9) If both subordinates respond PREPARED, the superior TM logs that
      the transaction is Committed, with recovery information (e.g.
      local and subordinate transaction identifiers, and subordinate TM
      IP addresses). The superior TM then sends COMMIT commands on the
      two subordinate TIP connections.

   10) The TMs at the airline and hotel servers perform the
       necessary steps to commit their local recoverable resources (e.g.
       by issuing xa_commit() requests). The subordinate TMs forget the
       transaction. The subordinate TMs then send COMITTED commands to
       the superior TM.

   11) The superior TM forgets the transaction. The TIP connections
       between the superior and subordinate TMs return to Idle state
       (not associated with any transaction). The superior TM returns
       success to the travel agency application "commit transaction"
       request.




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   12) The travel agency application returns "reservation made" to the
       client.

   This example illustrates the use of PULL. If PUSH were to be used
   instead, events 2) and 3) above would change as follows:

   2) The travel agency application:

      a.  passes the TIP URL obtained in 1. above, together with the
          listening endpoint address of the TM at the airline server, to
          its local TM via a "tip_push()" API request. The tip_push()
          function causes the following to occur:

          i. if a TIP connection does not already exist to the
             subordinate (airline server) TM (as identified via the IP
             address passed on the tip_push), one is created and an
             IDENTIFY exchange occurs (if multiplexing is to be used on
             the connection, this is followed by a MULTIPLEX exchange),

          ii. a PUSH command is sent to the subordinate TM,

          iii. in response to the PUSH, the subordinate TM creates a
               local transaction, associates this transaction with the
               connection, and sends a PUSHED response to the superior
               TM,

          iv. in response to the PUSHED response, the superior TM
              associates the subordinate TM with the transaction,

          v. the superior TM returns control to the travel agency
             application.

      b.  the travel agency application sends a request to the airline
         server (via some protocol (e.g. HTTP)), requesting the
         "book_flight" service, passing the flights selected by the
         client, and the TIP URL (obtained in 1 above).

   3) The request is received by the airline server which invokes the
      book_flight application. This application retrieves the TIP URL
      from the input data, and passes this on a "tip_pull()" API request
      to its local TM. Since the local TM has already "seen" this URL
      (it was already pushed), it simply returns to the book_flight
      application, which is now executing in the context of the
      previously created local transaction.







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   [Note that although in this example the transaction coordinator role
   is performed by a node which is also a participant in the transaction
   (the Travel Agency), other configurations are possible (e.g. where
   the transaction coordinator role is performed by a non-participant
   3rd-party node).]

8. TIP Transaction Recovery

   Until the transaction reaches the Prepared state, any failure results
   in the transaction being aborted. If an error occurs once the
   transaction has reached the Prepared state, then transaction recovery
   must be performed. Recovery behaviour is different for superior and
   subordinate; the details depend upon the outcome of the transaction
   (committed or aborted), and the precise point at which failure
   occurs.

   In the travel agency application for example, if the connection to
   the hotel server fails before the COMMIT command has been received by
   the hotel TM, then (once the connection is restored):

   1)  The superior (travel agency) TM sends a RECONNECT command
      (passing the subordinate transaction identifier (recovered from
      the transaction log if necessary)).

   2) The subordinate (hotel) TM responds RECONNECTED (since it never
      received the COMMIT command, and still has the transaction in
      Prepared state (if the failure had occurred after the subordinate
      had responded COMMITTED, then the subordinate would have forgotten
      the transaction, and responded NOTRECONNECTED to the RECONNECT
      command)).

   3) The superior TM sends a COMMIT command. The subordinate TM
      commits the transaction and responds COMMITTED. The transaction is
      now resolved.

   4) If the subordinate TM restores the connection to the superior TM
      before receiving a RECONNECT command, then it may send a QUERY
      command. In this case, the superior TM will respond QUERIEDEXISTS,
      and the subordinate TM should wait for the superior to send a
      RECONNECT command. If the transaction had been aborted, then the
      superior may respond QUERIEDNOTFOUND, in which case the
      subordinate should abort the transaction (note that the superior
      is not obliged to send a RECONNECT command for an aborted
      transaction (i.e. it could just forget the transaction after
      sending ABORT and before receiving an ABORTED response)).






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   There are failure circumstances in which the client application (the
   one calling "commit") may not receive a response indicating the final
   outcome of the transaction (even though the transaction itself is
   successfully completed). This is a common problem, and one not unique
   to TIP. In such circumstances, it is up to the application to
   ascertain the final outcome of the transaction (a TIP TM may
   facilitate this by providing some implementation specific mechanism.
   e.g. writing the outcome to a user-log).

9. TIP Transaction and Application Message Serialisation

   A relationship exists between TIP commands and application messages:
   a TIP transaction must not be committed until it is certain that all
   participants have properly registered, and have finished work on the
   transaction. Because of the two-pipe nature of TIP, this behaviour
   cannot necessarily be enforced by the TIP system itself (although it
   may be possible in some implementations). It is therefore incumbent
   upon the application to behave properly.  Generally, an application
   must not:

   1)  call it's local TMs "commit" function when it has any requests
       associated with the transaction still outstanding.

   2)  positively respond to a transactional request from a partner
       application prior to having registered it's local TM with the
       transaction.

10. TIP Protocol and Local Actions

   In order to ensure that transaction atomicity is properly guaranteed,
   a system implementing TIP must perform other local actions at certain
   points in the protocol exchange. These actions pertain to the
   creation and deletion of transaction "log-records" (the necessary
   information which survives failures and ensures that transaction
   recovery is correctly executed). The following information regarding
   the relationship between the TIP protocol and logging events is
   advisory, and is not intended to be definitive (see [2] for more
   discussion on this subject):

   1) before sending a PREPARED response, the system should create
      a prepared-recovery-record for the transaction.

   2) having created a prepared-recovery-record, this record should not
      be deleted until after:
      a.  an ABORT message is received; or
      b.  a COMMIT message is received; or
      c.  a QUERIEDNOTFOUND response is received.




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   3) the system should not send a COMMITTED or NOTRECONNECTED message
      if a prepared-recovery-record exists.

   4) before creating a commit-recovery-record for the transaction, the
      system should have received a PREPARED response.

   5) before sending a COMMIT message in Prepared state, the system
      should have created a commit-recovery-record for the transaction.

   6) having created a commit-recovery-record, this record should not be
      deleted until after:
      a.  a COMMITTED message is received; or
      b.  a NOTRECONNECTED message is received.

11. Security Considerations

   The means by which applications communicate and perform distributed
   work are outside the scope of the TIP protocol. The mechanisms used
   for authentication and authorisation of clients to access programs
   and information on a particular system are part of the application
   communications protocol and the application execution infrastructure.
   Use of the TIP protocol does not affect these considerations.

   Security relates to the TIP protocol itself inasmuch that systems
   require to protect themselves from the receipt of unauthorised TIP
   commands, or the impersonation of a trusted partner TIP TM.  Probably
   the worst consequence of this is the possibility of undetected data
   inconsistency resulting from violations of the TIP commitment
   protocol (e.g. a COMMIT command is injected on a TIP connection in
   place of an ABORT command). TIP uses the Transport Layer Security
   protocol [6] to restrict access to only trusted partners (i.e. to
   control from which remote endpoints TIP transactions will be
   accepted, and to verify that an end-point is genuine), and to encrypt
   TIP commands. Usage of TLS (or not) is negotiated between partner TIP
   TMs. See [1] for details of how TLS is used with TIP.

   TIP TM implementations will also likely provide local means to time-
   out and abort transactions which have not completed within some time
   period (thereby preventing unavailability of resources due to
   malicious intent). Transaction time-out also serves as a means of
   deadlock resolution.

12. TIP Requirements

   Most of these requirements stem from the primary objective of making
   transactions a ubiquitous system service, available to all
   application classes (much as TCP may be assumed to be available
   everywhere). In general this requires imposing as few restrictions



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   regarding the use of TIP as possible (applications should not be
   required to execute in some "special" environment in order to use
   transactions), and keeping the protocol simple and efficient. This
   enables the widespread implementation of TIP (it's cheap to do), on a
   wide range of systems (it's cheap to run).

   1) Application Communications Protocol Independence

      The TIP protocol must be defined independently of the
      communications protocol used for transferring application data, to
      allow TIP usage in conjunction with any application protocol.  It
      must be possible for applications using arbitrary communications
      protocols to begin, end, and propagate TIP transactions.

      This implies that the TIP protocol employ a 2-pipe model of
      operation. This model requires the separation of application
      communications and transaction coordination, into two discrete
      communication channels (pipes). This separation enables the use of
      the transaction coordination protocol (TIP), with any application
      communications protocol (e.g. HTTP, ODBC, plain TCP/UDP, etc).

   2) Support for Transaction Semantics

      The TIP protocol must provide the functionality of the de-facto
      standard presumed-abort 2-pc protocol, to guarantee transactional
      atomicity even in the event of failure. It should provide a means
      to construct the transaction tree, as well as provide commitment
      and recovery functions.

   3) Application Transaction Propagation and Interoperability

      In order to facilitate protocol independence, application
      interoperability, and provide a means for TIP transaction context
      propagation, a standard representation of the TIP transaction
      context information is required (in the form of a URL). This
      information must include the listening endpoint address of the
      partner TIP TM, and transaction identifier information.

   4) Ease of Implementation

      The TIP protocol must be simple to implement. It should support
      only those features necessary to provide a useful, performant 2-pc
      protocol service. The protocol should not add complexity in the
      form of extraneous optimisations.







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   5) Suitability for All Application Classes

      The TIP protocol should be complete and robust enough not only for
      electronic commerce on the web, but also for intranet applications
      and for traditional TP applications spanning heterogenous
      transaction manager environments. The protocol should be
      performant and scaleable enough to meet the needs of low to very
      high throughput applications.

      a. the TIP protocol should support the concept of client-only
         transaction participants (useful for ultra-lightweight
         implementations on low-end platforms).

      b. since some clients may be unreliable, TIP must provide support
         for delegation of transaction coordination (to a more reliable
         (trusted) node).

      c. the TIP protocol must scale between 1 and n (> 1) concurrent
         transactions per TCP connection.

      d. TIP commands should be able to be concatenated (pipelined).

      e. TIP should be compatible with the X/Open XA interface.

   6) Security

      The TIP protocol must be compatible with existing security
      mechanisms, potentially including encryption, firewalls, and
      authorization mechanisms (e.g. TLS may be used to authenticate the
      sender of a TIP command, and for encryption of TIP commands).
      Nothing in the protocol definition should prevent TIP working
      within any security environment.

   7) TIP Protocol Transport Independence

      It would be beneficial to some applications to allow the TIP
      protocol to flow over different transport protocols. The benefit
      is when using different transport protocols for the application
      data, the same transport can be used for the TIP 2PC protocol. TIP
      must therefore not preclude use with other transport protocols.

   8) Recovery

      Recovery semantics need to be defined sufficiently to avoid
      ambiguous results in the event of any type of communications
      transport failure.





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   9) Extensibility

      The TIP protocol should be able to be extended, whilst maintaining
      compatibility with previous versions.

References

   [1]  Lyon, J., Evans, K., and J. Klein, "The Transaction Internet
        Protocol Version 3.0", RFC 2371, July 1998.

   [2]  Transaction Processing: Concepts and Techniques.  Morgan
        Kaufmann Publishers. (ISBN 1-55860-190-2).  J. Gray, A. Reuter.

   [3]  X/Open CAE Specification, April 1995, Distributed Transaction
        Processing: The TX Specification. (ISBN 1-85912-094-6).

   [4]  X/Open Guide, November 1993, Distributed Transaction Processing:
        Reference Model Version 2. (ISBN 1-85912-019-9).

   [5]  X/Open CAE Specification, December 1991, Distributed Transaction
        Processing: The XA Specification.  (ISBN 1-872630-24-3).

   [6]  Dierks, T., et. al., "The TLS Protocol Version 1.0", Work in
        Progress.



























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Authors' Addresses

   Keith Evans
   Tandem Computers Inc, LOC 252-30
   5425 Stevens Creek Blvd
   Santa Clara, CA 95051-7200, USA

   Phone: +1 (408) 285 5314
   Fax:   +1 (408) 285 5245
   EMail: Keith.Evans@Tandem.Com


   Johannes Klein
   Tandem Computers Inc.
   10555 Ridgeview Court
   Cupertino, CA 95014-0789, USA

   Phone: +1 (408) 285 0453
   Fax:   +1 (408) 285 9818
   EMail: Johannes.Klein@Tandem.Com


   Jim Lyon
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052-6399, USA

   Phone: +1 (206) 936 0867
   Fax:   +1 (206) 936 7329
   EMail: JimLyon@Microsoft.Com

Comments

   Please send comments on this document to the authors at
   <JimLyon@Microsoft.Com>, <Keith.Evans@Tandem.Com>,
   <Johannes.Klein@Tandem.Com>, or to the TIP mailing list at
   <Tip@Tandem.Com>. You can subscribe to the TIP mailing list by
   sending  mail to <Listserv@Lists.Tandem.Com> with the line
   "subscribe tip <full name>" somewhere in the body of the message.












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Appendix A. An Example TIP Transaction Manager Application Programming
            Interface.

   Note that this API is included solely for informational purposes, and
   is not part of the formal TIP specification (TIP conformant
   implementations are free to define alternative APIs).

   1) tip_open() - establish a connection to a TIP TM.
      Synopsis
         int tip_open ([out] tip_handle_t *ptiptm)
      Parameters
         ptiptm [out]
                 Pointer to the TIP TM handle.
      Description
         tip_open() establishes a connection to a TIP TM. The call
         returns a handle which identifies the TIP TM. This function
         must be called before any work can be performed on a TIP
         transaction.

      Return Values
         [TIPOK]
               Connection has been successfully established.
         [TIPNOTCONNECTED]
               User has been disconnected from the TIP TM.
         [TIPNOTCONFIGURED]
               TIP TM has not been configured.
         [TIPTRANSIENT]
               Too many openers; re-try the open.
         [TIPERROR]
               An unexpected error occurred.

   2) tip_close() - close a connection to a TIP TM.
      Synopsis
         int tip_close([in] tip_handle_t handle)
      Parameters
         handle [in]
                 The TIP TM handle.
      Description
         tip_close() closes a connection to a TIP TM. All outstanding
         requests associated with that connection will be cancelled.
      Return Values
         [TIPOK]
               Connection has been successfully closed.
         [TIPINVALIDPARM]
               Invalid connection handle specified.
         [TIPERROR]
               An unexpected error occurred.




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   3) tip_push() - export a local transaction to a remote node and
                   return a TIP transaction identifier for the
                   associated remote transaction.
      Synopsis
         int tip_push ([in] tip_handle_t TM,
                       [in] char *tm_url,
                       [in] void *plocal_xid,
                       [out] char *pxid_url,
                       [in] unsigned int url_length)
      Parameters
         TM [in]
                 The TIP TM handle.
         tm_url [in]
                 Pointer to the TIP URL of the remote transaction manager.
                 A TIP URL for a transaction manager takes the form:
                 TIP://<host>[:<port>]
         plocal_xid [in]
                 Pointer to the local transaction identifier. The
                 structure of the transaction identifier is defined by the
                 local transaction manager.
         pxid_url [out]
                 Pointer to the TIP URL of the associated remote
                 transaction. A TIP URL for a transaction takes the form:
                 TIP://<host>[:<port>]/<transaction identifier>
         url_length [in]
                 The size in bytes of the buffer for the remote
                 transaction URL.
      Description
         tip_push() exports (pushes) a local transaction to a remote
         node. If a local transaction identifier is not supplied, the
         caller's current transaction context is used. The call returns
         a TIP URL for the associated remote transaction. The TIP
         transaction identifier may be passed on application requests to
         the remote node (as part of a TIP URL). The receiving process
         uses this information in order to do work on behalf of the
         transaction.
      Return Values
         [TIPOK]
               Transaction has been successfully pushed to the remote
               node.
         [TIPINVALIDXID]
               An invalid transaction identifier has been provided.
         [TIPNOCURRENTTX]
               Process is currently not associated with a transaction
               (and none was supplied).
         [TIPINVALIDHANDLE]
               Invalid connection handle specified.
         [TIPNOTPUSHED]



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               Transaction could not be pushed to the remote node.
         [TIPNOTCONNECTED]
               Caller has been disconnected from the TIP TM.
         [TIPINVALIDURL]
               Invalid endpoint URL is provided.
         [TIPTRANSIENT]
               Transient error occurred; re-try the operation.
         [TIPTRUNCATED]
               Insufficient buffer size is specified for the TIP
               transaction identifier.
         [TIPERROR]
               An unexpected error occurred.

   4) tip_pull() - create a local transaction and join it with the TIP
                   transaction.
      Synopsis
         int tip_pull([in] tip_handle_t TM,
                      [in] char *pxid_url,
                      [out] void *plocal_xid,
                      [in] unsigned int xid_length)
      Parameters
         TM [in]
               The TIP TM handle.
         pxid_url [in]
               Pointer to the TIP URL of the associated remote
               transaction. A TIP URL for a transaction takes the form:
               TIP://<host>[:<port>]/<transaction identifier>
         plocal_xid [out]
               Pointer to the local transaction identifier. The
               structure of the transaction identifier is defined by the
               local transaction manager.
         xid_length [in]
               The size in bytes of the buffer for the local transaction
               identifier.
      Description
         tip_pull() creates a local transaction and joins the local
         transaction with the TIP transaction (the caller becomes a
         subordinate participant in the TIP transaction). The remote TIP
         TM is identified via the URL (*pxid_url). The local transaction
         identifier is returned. If a local transaction has already been
         created for the TIP transaction identifier supplied, then
         [TIPOK] is returned (with the local transaction identifier),
         and no other action is taken.
      Return Values
         [TIPOK]
               The local transaction has been successfully created
               and joined with the TIP transaction.
         [TIPINVALIDHANDLE]



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               Invalid connection handle specified.
         [TIPTRUNCATED]
               Insufficient buffer size is specified for the local
               transaction identifier.
         [TIPNOTPULLED]
               Joining of the local transaction with the TIP
               transaction has failed.
         [TIPNOTCONNECTED]
               Caller has been disconnected from the TIP TM.
         [TIPINVALIDURL]
               Invalid URL has been supplied.
         [TIPTRANSIENT]
               Transient error occurred; retry the operation.
         [TIPERROR]
               An unexpected error occurred.

   5) tip_pull_async() - create a local transaction and join it with the
                         TIP transaction. Control is returned to the
                         caller as soon as a local transaction is
                         created.
      Synopsis
         int tip_pull_async ([in] tip_handle_t TM
                             [in] char *pxid_url,
                             [out] void *plocal_xid,
                             [in] unsigned int xid_length)
      Parameters
         TM [in]
               The TIP gateway handle.
         pxid_url [in]
               Pointer to the TIP URL of the associated remote
               transaction. A TIP URL for a transaction takes the form:
               TIP://<host>[:<port>]/<transaction identifier>
         plocal_xid [out]
               Pointer to the local transaction identifier. The
               structure of the transaction identifier is defined by the
               local transaction manager.
         xid_length [in]
               The size in bytes of the buffer for the local transaction
               identifier.
      Description
         tip_pull_async() creates a local transaction and joins the
         local transaction with the TIP transaction (the caller
         becomes a subordinate participant in the TIP transaction). The
         remote TIP TM is identified via the URL (*pxid_url). The local
         transaction identifier is returned. A call to tip_pull_async()
         returns immediately after the local transaction has been
         created (before the TIP PULL protocol command is sent). A
         subsequent call to tip_pull_complete() must be issued to check



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         for successful completion of the pull request.
      Return Values
         [TIPOK]
               The local transaction has been successfully created.
         [TIPINVALIDHANDLE]
               Invalid connection handle specified.
         [TIPNOTCONNECTED]
               User has been disconnected from the TIP TM.
         [TIPINVALIDURL]
               Invalid URL has been supplied.
         [TIPTRANSIENT]
               Transient error has occurred; retry the operation.
         [TIPTRUNCATED]
               Insufficient buffer size is specified for the local
               transaction identifier.
         [TIPERROR]
               An unexpected error occurred.

   6) tip_pull_complete() - check whether a previous tip_pull_async()
                            request has been successfully completed.
      Synopsis
         int tip_pull_complete ([in] tip_handle_t TM,
                                [in] void *plocal_xid)
      Parameters
         TM [in]
               The TIP TM handle.
         plocal_xid [in]
               Pointer to the local transaction identifier. The
               structure of the transaction identifier is defined by the
               local transaction manager.
      Description
         tip_pull_complete() checks whether a previous call to
         tip_pull_async() has been successfully completed. i.e. whether
         the local transaction has been successfully joined with the TIP
         transaction. The caller supplies the local transaction
         identifier returned by the previous call to tip_pull_async().
         Repeated calls to tip_pull_complete() for the same local
         transaction identifier are idempotent.
      Return Values
         [TIPOK]
               The local transaction has been successfully joined with
               the TIP transaction.
         [TIPINVALIDHANDLE]
               Invalid connection handle specified.
         [TIPINVALIDXID]
               An invalid transaction identifier has been provided.
         [TIPNOTPULLED]
               Joining of the local transaction with the TIP transaction



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               has failed. The local transaction has been aborted.
         [TIPNOTCONNECTED]
               Caller has been disconnected from the TIP TM.
         [TIPERROR]
               An unexpected error occurred.

   7) tip_xid_to_url() - return a TIP transaction identifier for a local
                         transaction identifier.
      Synopsis
         int tip_xid_to_url ([in] tip_handle_t TM,
                             [in] void *plocal_xid,
                             [out] char *pxid_url,
                             [in] unsigned int url_length)
      Parameters
         TM [in]
               The TIP TM handle.
         plocal_xid [in]
               Pointer to the local transaction identifier. The
               structure of the transaction identifier is defined by the
               local transaction manager.
         pxid_url [out]
               Pointer to the TIP URL of the local transaction.
               A TIP URL for a transaction takes the form:
               TIP://<host>[:<port>]/<transaction identifier>
         url_length [in]
               The size in bytes of the buffer for the TIP URL.
      Description
         tip_xid_to_url() returns a TIP transaction identifier for a
         local transaction identifier. The TIP transaction identifier
         can be passed to remote applications to enable them to do work
         on the transaction. e.g. to pull the local transaction to the
         remote node. If a local transaction identifier is not supplied,
         the caller's current transaction context is used. The constant
         TIPURLSIZE defines the size of a TIP transaction identifier in
         bytes. This value is implementation specific.
      Return Values
         [TIPOK]
               TIP transaction identifier has been returned.
         [TIPNOTCONNECTED]
               Caller has been disconnected from the TIP TM.
         [TIPNOCURRENTTX]
               Process is currently not associated with a transaction
               (and none was supplied).
         [TIPINVALIDXID]
               An invalid local transaction identifier has been
               supplied.
         [TIPTRUNCATED]
               Insufficient buffer size is specified for the TIP



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               transaction identifier.
         [TIPERROR]
               An unexpected error occurred.

   8) tip_url_to_xid() - return a local transaction identifier for a TIP
                         transaction identifier.
      Synopsis
           int tip_url_to_xid ([in] tip_handle_t TM,
                             [in] char *pxid_url,
                             [out] void *plocal_xid,
                             [in] unsigned int xid_length)
      Parameters
         TM [in]
               The TIP TM handle.
         pxid_url [in]
               Pointer to the TIP URL of the local transaction. A TIP
               URL for a transaction takes the form:
               TIP://<host>[:<port>]/<transaction identifier>
         plocal_xid [out]
               Pointer to the local transaction identifier. The
               structure of the transaction identifier is defined by the
               local transaction manager.
         xid_length [in]
               The size in bytes of the buffer for the local transaction
               identifier.
      Description
         tip_url_to_xid() returns a local transaction identifier for a
         TIP transaction identifier (note that the local transaction
         must have previously been created via a tip_push(), or tip_pull
         (or tip_pull_async()). The constant TIPXIDSIZE defines the size
         of a local transaction identifier in bytes. This value is
         implementation specific.
      Return Values
         [TIPOK]
               Local transaction identifier is returned.
         [TIPINVALIDURL]
               An invalid TIP transaction identifier has been provided.
         [TIPTRUNCATED]
               Insufficient buffer size is specified for the local
               transaction identifier.
         [TIPERROR]
               An unexpected error occurred.









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9)  tip_get_tm_url() - get the name of the local TIP transaction
                       manager in TIP URL form.
    Synopsis
       int tip_get_tm_url ([in] tip_handle_t TM,
                           [out] char *tm_url,
                           [in] int tm_len);
    Parameters
       TM[in]
            The TIP TM handle.
       tm_url [in]
            Pointer to the TIP URL of the local transaction manager. A
            TIP URL for a transaction manager takes the form:
            TIP://<host>[:<port>]
       tm_len [out]
            The size in bytes of the buffer for the TIP URL of the local
            transaction manager.
    Description
       tip_get_tm_url() gets the name of the  local transaction
       manager in TIP URL form (i.e. TIP://<host>[:<port>])
    Return Values
       [TIPOK]
             The name of the local transaction manager has been
             successfully returned.
       [TIPTRUNCATED]
             The name of the local transaction manager has been
             truncated due to insufficient buffer size. Retry the
             operation with larger buffer size.
























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Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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