Accept-Encoding - HTTP

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Accept-Encoding request HTTP header advertises which content encoding, usually a compression algorithm, the client is able to understand. Using content negotiation , the server selects one of the proposals, uses it and informs the client of its choice with the Content-Encoding response header.

Even if both the client and the server supports the same compression algorithms, the server may choose not to compress the body of a response, if the identity value is also acceptable. Two common cases lead to this:

The data to be sent is already compressed and a second compression won't lead to smaller data to be transmitted. This may be the case with some image formats;
The server is overloaded and cannot afford the computational overhead induced by the compression requirement. Typically, Microsoft recommends not to compress if a server uses more than 80% of its computational power.

As long as the identity value, meaning no encoding, is not explicitly forbidden, by an identity;q=0 或 *;q=0 without another explicitly set value for identity, the server must never send back a 406 Not Acceptable error.

注意事项：

An IANA registry maintains a complete list of official content encodings .
Two others content encoding, bzip and bzip2 , are sometimes used, though not standard. They implement the algorithm used by these two UNIX programs. Note that the first one was discontinued due to patent licensing problems.

Header type	Request header
Forbidden header name	yes

句法

Accept-Encoding: gzip
Accept-Encoding: compress
Accept-Encoding: deflate
Accept-Encoding: br
Accept-Encoding: identity
Accept-Encoding: *
// Multiple algorithms, weighted with the quality value syntax:
Accept-Encoding: deflate, gzip;q=1.0, *;q=0.5

指令

gzip: A compression format using the Lempel-Ziv coding (LZ77), with a 32-bit CRC.
compress: A compression format using the Lempel-Ziv-Welch (LZW) algorithm.
deflate: A compression format using the zlib structure, with the deflate compression algorithm.
br: A compression format using the Brotli algorithm.
identity
*
;q= (qvalues weighting): Any value is placed in an order of preference expressed using a relative quality value called weight .

范例

Accept-Encoding: gzip
Accept-Encoding: gzip, compress, br
Accept-Encoding: br;q=1.0, gzip;q=0.8, *;q=0.1

规范

规范	Title
RFC 7231, section 5.3.4: Accept-Encoding	Hypertext Transfer Protocol (HTTP/1.1): Semantics and Context

浏览器兼容性

更新 GitHub 上的兼容性数据

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`Accept-Encoding`	Chrome 完整支持 Yes	Edge 完整支持 12	Firefox 完整支持 Yes	IE 完整支持 Yes	Opera 完整支持 Yes	Safari 完整支持 Yes	WebView Android 完整支持 Yes	Chrome Android 完整支持 Yes	Firefox Android 完整支持 Yes	Opera Android 完整支持 Yes	Safari iOS 完整支持 Yes	Samsung Internet Android 完整支持 Yes

图例

完整支持

另请参阅

HTTP content negotiation
Header with the result of the content negotiation: Content-Encoding
Other similar headers: TE , Accept , Accept-Charset , Accept-Language

元数据

最后修改： Feb 8, 2020

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句法

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