HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 10:03:27 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Sat, 16 Nov 1996 00:16:00 GMT ETag: "361e70-1a99-328d07c0" Accept-Ranges: bytes Content-Length: 6809 Connection: close Content-Type: text/plain Internet-Draft Larry Masinter draft-masinter-url-data-02.txt Xerox Corporation Expires in 6 months November 13, 1996 The "data" URL scheme Status of This Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). 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. 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:[][;base64], The is an Internet media type specification (with optional parameters, etc.) 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 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 intended for short values. Many applications that use URLs may impose a length limit; for example, URLs embedded within anchors in HTML have a length limit determined by the SGML declaration for HTML[RFC1866]. The "data" URL scheme has no relative URL forms. Syntax dataurl := "data:" [ mediatype [ ";base64" ] "," data mediatype := type "/" subtype *( ";" parameter ) data := *urlchar parameter := attribute "=" value where "urlchar" is imported from [RFC-URL-SYNTAX], and "type", "subtype", "attribute" and "value" are the corresponding tokens from [RFC 1522], represented using URL escaped encoding of [RFC-URL-SYNTAX] as necessary. Attribute values in [RFC 1522] 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. 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: Larry 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. 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. 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. 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. References [RFCSYNTAX] RFC xxxx. Uniform Resource Locators (URL). R. Fielding, L. Masinter, T. Berners-Lee, December 1996. [RFC1866] RFC 1866: Hypertext Markup Language - 2.0. T. Berners-Lee & D. Connolly. November 1995. [RFC1522] RFC 1522: MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies Author contact information: Larry Masinter Xerox Palo Alto Research Center 3333 Coyote Hill Road Palo Alto, CA 94304 masinter@parc.xerox.com