HTTP compression: Difference between revisions

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'''HTTP compression''' is a capability that can be built into [[web server]]s and [[web client]]s to improve transfer speed and bandwidth utilization.<ref>{{cite web|url=http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/d52ff289-94d3-4085-bc4e-24eb4f312e0e.mspx?mfr=true|title=Using HTTP Compression (IIS 6.0)|access-date=9 February 2010|publisher=Microsoft Corporation}}</ref>

HTTP data is [[Data compression|compressed]] before it is sent from the server: compliant browsers will announce what methods are supported to the server before downloading the correct format; browsers that do not support compliant compression method will download uncompressed data. The most common compression schemes include [[gzip]] and [[DeflateBrotli]]; however, a full list of available schemes is maintained by the [[Internet Assigned Numbers Authority|IANA]].<ref>RFC 2616, Section 3.5: "The Internet Assigned Numbers Authority (IANA) acts as a registry for content-coding value tokens."</ref> Additionally, third parties develop new methods and include them in their products, such as the Google [[Shared Dictionary Compression for HTTP]] (SDCH) scheme implemented in the [[Google Chrome]] browser and used on Google servers.

There are two different ways compression can be done in HTTP. At a lower level, a Transfer-Encoding header field may indicate the payload of an HTTP message is compressed. At a higher level, a Content-Encoding header field may indicate that a resource being transferred, cached, or otherwise referenced is compressed. Compression using Content-Encoding is more widely supported than Transfer-Encoding, and some browsers do not advertise support for Transfer-Encoding compression to avoid triggering bugs in servers.<ref>[https://code.google.com/p/chromium/issues/detail?id=94730 'RFC2616 "Transfer-Encoding: gzip, chunked" not handled properly'], [[Chromium (browser)|Chromium]] Issue 94730</ref>