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8. Content Parameters
Encoding mechanism values are used to indicate an encoding transformation that has been or can be applied to a resource. Encoding mechanisms are primarily used to allow a document to be compressed or encrypted without losing the identity of its underlying media type. Typically, the resource is stored with this encoding and is only decoded before rendering or analogous usage.
encoding-mechanism = "gzip" | "compress" | token
Note
For historical reasons, HTTP/1.0 applications should consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress", respectively.
All encoding-mechanism values are case-insensitive. HTTP/1.0 uses encoding-mechanism values in the Accept-Encoding (Section 5.4.3) and Content-Encoding (Section 7.1.2) header fields. Although the value describes the encoding-mechanism, what is more important is that it indicates what decoding mechanism will be required to remove the encoding. Note that a single program may be capable of decoding multiple encoding-mechanism formats. Two values are defined by this specification:
- gzip
- An encoding format produced by the file compression program "gzip" (GNU zip) developed by Jean-loup Gailly. This format is typically a Lempel-Ziv coding (LZ77) with a 32 bit CRC. Gzip is available from the GNU project at <URL:ftp://prep.ai.mit.edu/pub/gnu/>.
- compress
- The encoding format produced by the file compression program "compress". This format is an adaptive Lempel-Ziv-Welch coding (LZW).
T. Berners-Lee, R. T. Fielding, H. Frystyk Nielsen - 12 MAR 95
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