HTTP Compression - Client/Server Compression Scheme Negotiation

Client/Server Compression Scheme Negotiation

In most cases, excluding the SDCH, the negotiation is done in two steps, described in the RFC 2616:

1. The web client includes an Accept-Encoding field in the HTTP request, with supported compression schema names (called content-coding tokens), separated by commas.

GET /encrypted-area HTTP/1.1 Host: www.example.com Accept-Encoding: gzip, deflate

2. If the server supports one or more compression schemas, the outgoing data may be compressed by one or more methods supported by both parties. If this is the case, the server will add a Content-Encoding field in the HTTP response with the used schemas, separated by commas.

HTTP/1.1 200 OK Date: Mon, 23 May 2005 22:38:34 GMT Server: Apache/1.3.3.7 (Unix) (Red-Hat/Linux) Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT Etag: "3f80f-1b6-3e1cb03b" Accept-Ranges: bytes Content-Length: 438 Connection: close Content-Type: text/html; charset=UTF-8 Content-Encoding: gzip

The web server is by no means obligated to use any compression method - this depends on the internal settings of the web server and also may depend on the internal architecture of the website in question.

In case of SDCH a dictionary negotiation is also required, which may involve additional steps, like downloading a proper dictionary from the external server.

Read more about this topic:  HTTP Compression

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