Connected: An Internet Encyclopedia
3.5 Content Codings

Up: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 2068
Up: 3 Protocol Parameters
Prev: 3.4 Character Sets
Next: 3.6 Transfer Codings

3.5 Content Codings

3.5 Content Codings

Content coding values indicate an encoding transformation that has been or can be applied to an entity. Content codings are primarily used to allow a document to be compressed or otherwise usefully transformed without losing the identity of its underlying media type and without loss of information. Frequently, the entity is stored in coded form, transmitted directly, and only decoded by the recipient.

          content-coding   = token

All content-coding values are case-insensitive. HTTP/1.1 uses content-coding values in the Accept-Encoding (section 14.3) and Content-Encoding (section 14.12) header fields. Although the value describes the content-coding, what is more important is that it indicates what decoding mechanism will be required to remove the encoding.

The Internet Assigned Numbers Authority (IANA) acts as a registry for content-coding value tokens. Initially, the registry contains the following tokens:

gzip
An encoding format produced by the file compression program "gzip" (GNU zip) as described in RFC 1952 [25]. This format is a Lempel- Ziv coding (LZ77) with a 32 bit CRC.

compress
The encoding format produced by the common UNIX file compression program "compress". This format is an adaptive Lempel-Ziv-Welch coding (LZW).

deflate
The "zlib" format defined in RFC 1950[31] in combination with the "deflate" compression mechanism described in RFC 1951[29].

New content-coding value tokens should be registered; to allow interoperability between clients and servers, specifications of the content coding algorithms needed to implement a new value should be publicly available and adequate for independent implementation, and conform to the purpose of content coding defined in this section.


Next: 3.6 Transfer Codings

Connected: An Internet Encyclopedia
3.5 Content Codings