WDIFF

draft-masinter-url-data-00.txt --> draft-masinter-url-data-01.txt

"Data: URL scheme"

Status of This Memo

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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 proposal includes document defines a new URL
scheme that would work like 'immediate addressing'. The format URLs are of
the URL is as follows:

data:<mediatype>[;base64],<encoded-value>

where <mediatime> form:

data:[<mediatype>][;base64],<value>

The <mediatype> is a an Internet media type specification (with optional
parameters, etc.). etc.) The token "base64" appearance of ";base64" means that the value is
encoded as base64.
Otherwise, Without ";base64", the value (as a sequence of
octets) is represented directly; octets outside of the range
representable by safe URL characters should be encoded with using the
standard %xx URL encoding.

The mediatype, if left blank, hex encoding of URLs. 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.

Examples:

This

The "data:" URL scheme is only to be used useful for very short data types. For 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 HTML DTD.

Examples

A data: URL might be used for arbitrary types of data.

data:,A%20brief%20note

encodes the text/plain string "A brief note" note", which might be useful in
a footnote link, while, link.

The HTML fragment:

could be used for a small inline image in a HTML document.

This is only appropriate for delivery of very small inline data. The (The
embedded image above is probably near the limit of utility. For anything
else larger, or where the base64 encoding is problematic or
cumbersome, immediate data references within URLs are inappropriate. likely to be inappropriate.)

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 by the author, and
recently revised because 1995. Some versions of the appearance
data URL scheme have been used in the definition of VRML, and a
version has appeared as part of a (weaker) proposal for embedded data in
a HTML INSERT proposal. This version allows eliding HTML.
Various changes have been made, based on requests, to elide the media
type,
packs pack the indication of the base64 encoding more tightly, and
eliminates the proposal to allow quoted printable, since the
eliminate "quoted printable" as an encoding since it would not easily
yield valid URLs without additional %xx encoding, which itself is
sufficient.

Security

Immediate data URLs introduce no new security considerations.

References

[RFC1738] RFC 1738. Uniform Resource Locators (URL). T.
Berners-Lee, L. Masinter & M. McCahill. December 1994.

[RFC1808] RFC 1808. Relative Uniform Resource Locators. R.
Fielding. June 1995.

Author contact information:

Larry Masinter
Xerox Palo Alto Research Center
3333 Coyote Hill Road
Palo Alto, CA 94304
masinter@parc.xerox.com

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