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+Network Working Group                                      L. Masinter
+Request for Comments: 2397                           Xerox Corporation
+Category: Standards Track                                  August 1998
+
+
+                         The "data" URL scheme
+
+Status of this Memo
+
+   This document specifies an Internet standards track protocol for the
+   Internet community, and requests discussion and suggestions for
+   improvements.  Please refer to the current edition of the "Internet
+   Official Protocol Standards" (STD 1) for the standardization state
+   and status of this protocol.  Distribution of this memo is unlimited.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (1998).  All Rights Reserved.
+
+1. Abstract
+
+   A new URL scheme, "data", is defined. It allows inclusion of small
+   data items as "immediate" data, as if it had been included
+   externally.
+
+2. Description
+
+   Some applications that use URLs also have a need to embed (small)
+   media type data directly inline. This document defines a new URL
+   scheme that would work like 'immediate addressing'. The URLs are of
+   the form:
+
+                    data:[<mediatype>][;base64],<data>
+
+   The <mediatype> is an Internet media type specification (with
+   optional parameters.) The appearance of ";base64" means that the data
+   is encoded as base64. Without ";base64", the data (as a sequence of
+   octets) is represented using ASCII encoding for octets inside the
+   range of safe URL characters and using the standard %xx hex encoding
+   of URLs for octets outside that range.  If <mediatype> is omitted, it
+   defaults to text/plain;charset=US-ASCII.  As a shorthand,
+   "text/plain" can be omitted but the charset parameter supplied.
+
+   The "data:" URL scheme is only useful for short values. Note that
+   some applications that use URLs may impose a length limit; for
+   example, URLs embedded within <A> anchors in HTML have a length limit
+   determined by the SGML declaration for HTML [RFC1866]. The LITLEN
+   (1024) limits the number of characters which can appear in a single
+
+
+
+Masinter                    Standards Track                     [Page 1]
+
+RFC 2397                 The "data" URL scheme               August 1998
+
+
+   attribute value literal, the ATTSPLEN (2100) limits the sum of all
+   lengths of all attribute value specifications which appear in a tag,
+   and the TAGLEN (2100) limits the overall length of a tag.
+
+   The "data" URL scheme has no relative URL forms.
+
+3. Syntax
+
+       dataurl    := "data:" [ mediatype ] [ ";base64" ] "," data
+       mediatype  := [ type "/" subtype ] *( ";" parameter )
+       data       := *urlchar
+       parameter  := attribute "=" value
+
+   where "urlchar" is imported from [RFC2396], and "type", "subtype",
+   "attribute" and "value" are the corresponding tokens from [RFC2045],
+   represented using URL escaped encoding of [RFC2396] as necessary.
+
+   Attribute values in [RFC2045] are allowed to be either represented as
+   tokens or as quoted strings. However, within a "data" URL, the
+   "quoted-string" representation would be awkward, since the quote mark
+   is itself not a valid urlchar. For this reason, parameter values
+   should use the URL Escaped encoding instead of quoted string if the
+   parameter values contain any "tspecial".
+
+   The ";base64" extension is distinguishable from a content-type
+   parameter by the fact that it doesn't have a following "=" sign.
+
+4. Examples
+
+   A data URL might be used for arbitrary types of data. The URL
+
+                          data:,A%20brief%20note
+
+   encodes the text/plain string "A brief note", which might be useful
+   in a footnote link.
+
+   The HTML fragment:
+
+   <IMG
+   SRC="data:image/gif;base64,R0lGODdhMAAwAPAAAAAAAP///ywAAAAAMAAw
+   AAAC8IyPqcvt3wCcDkiLc7C0qwyGHhSWpjQu5yqmCYsapyuvUUlvONmOZtfzgFz
+   ByTB10QgxOR0TqBQejhRNzOfkVJ+5YiUqrXF5Y5lKh/DeuNcP5yLWGsEbtLiOSp
+   a/TPg7JpJHxyendzWTBfX0cxOnKPjgBzi4diinWGdkF8kjdfnycQZXZeYGejmJl
+   ZeGl9i2icVqaNVailT6F5iJ90m6mvuTS4OK05M0vDk0Q4XUtwvKOzrcd3iq9uis
+   F81M1OIcR7lEewwcLp7tuNNkM3uNna3F2JQFo97Vriy/Xl4/f1cf5VWzXyym7PH
+   hhx4dbgYKAAA7"
+   ALT="Larry">
+
+
+
+
+Masinter                    Standards Track                     [Page 2]
+
+RFC 2397                 The "data" URL scheme               August 1998
+
+
+   could be used for a small inline image in a HTML document.  (The
+   embedded image is probably near the limit of utility. For anything
+   else larger, data URLs are likely to be inappropriate.)
+
+   A data URL scheme's media type specification can include other
+   parameters; for example, one might specify a charset parameter.
+
+      data:text/plain;charset=iso-8859-7,%be%fg%be
+
+   can be used for a short sequence of greek characters.
+
+   Some applications may use the "data" URL scheme in order to provide
+   setup parameters for other kinds of networking applications. For
+   example, one might create a media type
+           application/vnd-xxx-query
+
+   whose content consists of a query string and a database identifier
+   for the "xxx" vendor's databases. A URL of the form:
+
+   data:application/vnd-xxx-
+   query,select_vcount,fcol_from_fieldtable/local
+
+   could then be used in a local application to launch the "helper" for
+   application/vnd-xxx-query and give it the immediate data included.
+
+5. History
+
+   This idea was originally proposed August 1995. Some versions of the
+   data URL scheme have been used in the definition of VRML, and a
+   version has appeared as part of a proposal for embedded data in HTML.
+   Various changes have been made, based on requests, to elide the media
+   type, pack the indication of the base64 encoding more tightly, and
+   eliminate "quoted printable" as an encoding since it would not easily
+   yield valid URLs without additional %xx encoding, which itself is
+   sufficient. The "data" URL scheme is in use in VRML, new applications
+   of HTML, and various commercial products. It is being used for object
+   parameters in Java and ActiveX applications.
+
+6. Security
+
+   Interpretation of the data within a "data" URL has the same security
+   considerations as any implementation of the given media type.  An
+   application should not interpret the contents of a data URL which is
+   marked with a media type that has been disallowed for processing by
+   the application's configuration.
+
+
+
+
+
+
+Masinter                    Standards Track                     [Page 3]
+
+RFC 2397                 The "data" URL scheme               August 1998
+
+
+   Sites which use firewall proxies to disallow the retrieval of certain
+   media types (such as application script languages or types with known
+   security problems) will find it difficult to screen against the
+   inclusion of such types using the "data" URL scheme.  However, they
+   should be aware of the threat and take whatever precautions are
+   considered necessary within their domain.
+
+   The effect of using long "data" URLs in applications is currently
+   unknown; some software packages may exhibit unreasonable behavior
+   when confronted with data that exceeds its allocated buffer size.
+
+7. References
+
+   [RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter,
+               "Uniform Resource Identifiers (URI): Generic Syntax", RFC
+               2396, August 1998.
+
+   [RFC1866]   Berners-Lee, T., and D. Connolly, "Hypertext Markup
+               Language - 2.0.", RFC 1866, November 1995.
+
+   [RFC2045]   Freed N., and N. Borenstein., "Multipurpose Internet Mail
+               Extensions (MIME) Part One: Format of Internet Message
+               Bodies", RFC 2045, November 1996.
+
+Author contact information:
+
+   Larry Masinter
+   Xerox Palo Alto Research Center
+   3333 Coyote Hill Road
+   Palo Alto, CA 94304
+
+   EMail: masinter@parc.xerox.com
+
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+Masinter                    Standards Track                     [Page 4]
+
+RFC 2397                 The "data" URL scheme               August 1998
+
+
+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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+Masinter                    Standards Track                     [Page 5]
+