Schema of non-pipelined vs. pipelined connection.

HTTP pipelining is a technique in which multiple HTTP requests are sent on a single TCP connection without waiting for the corresponding responses.[1]

The pipelining of requests results in a dramatic improvement[2] in the loading times of HTML pages, especially over high latency connections such as satellite Internet connections.

Since it is usually possible to fit several HTTP requests in the same TCP packet, HTTP pipelining allows fewer TCP packets to be sent over the network, reducing network load.

Non-idempotent methods like POST should not be pipelined. Sequences of GET and HEAD requests can be always pipelined. A sequence of other idempotent requests like GET, HEAD, PUT and DELETE can be pipelined or not depending on whether requests in the sequence depend on the effect of others.[3]

HTTP pipelining requires both the client and the server to support it. HTTP/1.1 conforming servers are required to support pipelining. This does not mean that servers are required to pipeline responses, but that they are required not to fail if a client chooses to pipeline requests.

Contents

[hide]

  • 1 Implementation status

    • 1.1 Implementation in web servers
    • 1.2 Implementation in web browsers
    • 1.3 Implementation in web proxies
    • 1.4 Other implementations
  • 2 See also
  • 3 References
  • 4 External links

[edit] Implementation status

Pipelining is only supported in HTTP/1.1, not in 1.0.

[edit] Implementation in web servers

Implementing pipelining in web servers is a relatively simple matter of making sure that network buffers are not discarded between requests. For that reason, most modern web servers handle pipelining without any problem.

[edit] Implementation in web browsers

Out of all the major browsers, only Opera has a fully working implementation that is enabled by default. All other browsers HTTP pipelining is disabled or not implemented.[4]

  • Internet Explorer 8 does not pipeline requests, due to concerns regarding buggy proxies and head-of-line blocking.[5]
  • Mozilla browsers (such as Mozilla Firefox, SeaMonkey and Camino) support pipelining, however it is disabled by default.[6][7] Pipelining is disabled by default to avoid issues with misbehaving servers.[8] When pipelining is enabled, Mozilla browsers use some heuristics, especially to turn pipelining off for older IIS servers.[9]
  • Konqueror 2.0 supports pipelining, but it's disabled by default.[citation needed]
  • Google Chrome does not support pipelining in the stable release (as of version 17), but version 18 beta supports pipelining http (but not https) as a non-default option (was previously in unstable builds[10] and Chromium as a launch parameter[11]).

[edit] Implementation in web proxies

Most HTTP proxies do not pipeline outgoing requests.[12]

Some versions of the Squid web proxy will pipeline up to two outgoing requests. This functionality has been disabled by default and needs to be manually enabled for "bandwidth management and access logging reasons."[13] Squid supports multiple requests from clients.

The Polipo proxy pipelines outgoing requests.[14]

[edit] Other implementations

The libwww library made by the World Wide Web Consortium, supports pipelining since version 5.1 released at 18 February 1997.[15]

Other application development libraries that support HTTP pipelining include:

  • Perl modules providing client support for HTTP pipelining are HTTP::Async and the LWPng (libwww-perl New Generation) library.[16]
  • Apache Foundation project HttpComponents provides pipelining support in the HttpCore NIO extensions.
  • The Microsoft .Net Framework 3.5 supports HTTP pipelining in the module System.Net.HttpWebRequest.[17]
  • Qt class QNetworkRequest, introduced in 4.4, supports HTTP Pipelining.[18]

Some other applications currently exploiting pipelining are:

  • phttpget from FreeBSD (a minimalist pipelined HTTP client)
  • libcurl has limited support for pipelining using the CURLMOPT_PIPELINING option.[citation needed]
  • portsnap (a FreeBSD ports tree distribution system)
  • Advanced Packaging Tool support pipelining.[citation needed]
  • Subversion has optional support for HTTP pipelining with the serf WebDAV access module (the default module, neon does not have pipelining support).[19][20]
  • Microsoft Message Queuing on Windows Server 2003 utilises pipelining on HTTP by default, and can be configured to use it on HTTPS.[21] IBM CICS 3.1 supports HTTP pipelining within its client.[22]
  • Pipelined::HttpClient is a C++ client library based on pipelining.[23]

Multipart XHR is implementation of pipelining (without any browser or web server support) done purely in Javascript in combination with server side scripting.[citation needed]

Testing tools which support HTTP pipelining include:

  • httperf [24]

[edit] See also

  • HTTP persistent connection
  • WebSockets
  • SPDY

[edit] References

  1. "part of Hypertext Transfer Protocol -- HTTP/1.1 Section 8.1.2.2 Pipelining". W3C. June 1999. http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.1.2.2. Retrieved 2011-09-16.
  2. Nielsen, Henrik Frystyk; Gettys, Jim; Baird-Smith, Anselm; Prud'hommeaux, Eric; Lie, Håkon Wium; Lilley, Chris (24 June 1997). "Network Performance Effects of HTTP/1.1, CSS1, and PNG". World Wide Web Consortium. http://www.w3.org/Protocols/HTTP/Performance/Pipeline.html. Retrieved 14 January 2010.
  3. "part of Hypertext Transfer Protocol -- HTTP/1.1 Section 9.1.2 Idempotent Methods". W3C. June 1999. http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2. Retrieved 2009-05-16.
  4. Willis, Nathan (18 November 2009). "Reducing HTTP latency with SPDY". LWN.net. http://lwn.net/Articles/362473/.
  5. "Windows Internet Explorer 8 Expert Zone Chat (August 14, 2008)". Microsoft. August 14, 2008. http://www.microsoft.com/windowsxp/expertzone/chats/transcripts/08_0814_ez_ie8.mspx. Retrieved 2009-03-27.
  6. http://kb.mozillazine.org/Network.http.pipelining
  7. Cheah Chu Yeow. Firefox secrets. p.180. ISBN0975240242.
  8. "https://bugzilla.mozilla.org/show_bug.cgi?id=264354". Mozilla. https://bugzilla.mozilla.org/show_bug.cgi?id=264354. Retrieved 2011-09-16.
  9. "Source code – nsHttpConnection.cpp". Firefox source code. Mozilla. 7 May 2010. https://hg.mozilla.org/releases/mozilla-2.0/file/09565753ce5f/netwerk/protocol/http/src/nsHttpConnection.cpp#l251. Retrieved 5 December 2010.
  10. "Issue 8991: Optional HTTP pipelining mode". Google. 19 March 2009. http://code.google.com/p/chromium/issues/detail?id=8991. Retrieved 16 May 2009.
  11. Gary Mark (20 October 2011). "HTTP Pipelining In Google Chrome". BrowserFame.com. http://browserfame.com/281/http-pipelining-in-google-chrome. Retrieved 20 October 2011.
  12. Mark Nottingham (20 June 2007). "The State of Proxy Caching". http://www.mnot.net/blog/2007/06/20/proxy_caching. Retrieved 2009-05-16.
  13. "squid: pipeline_prefetch configuration directive". Squid. November 9, 2009. http://www.squid-cache.org/Doc/config/pipeline_prefetch/. Retrieved 2009-12-01.
  14. "Polipo — a caching web proxy". Juliusz Chroboczek. September 18, 2009. http://www.pps.jussieu.fr/~jch/software/polipo/. Retrieved 2009-11-12.
  15. Kahan, José (7 June 2002). "Change History of libwww". World Wide Web Consortium. http://www.w3.org/Library/User/History.html. Retrieved 3 August 2010.
  16. Using HTTP::Async for Parallel HTTP Requests (Colin Bradford)
  17. System.Net.HttpWebRequest & pipelining
  18. QNetworkRequest Class Reference, Nokia QT documentation
  19. C. Michael Pilato, Ben Collins-Sussman, Brian W. Fitzpatrick (2008). Version Control with Subversion. O'Reilly Media. p.238. ISBN0596510330.
  20. Justin R. Erenkrantz (2007). "Subversion: Powerful New Toys". http://www.erenkrantz.com/oscon/OSCON%202007%20Subversion%20New%20Toys.pdf.
  21. "HTTP/HTTPS messages". Microsoft TechNet. January 21, 2005. http://technet.microsoft.com/en-us/library/cc737394%28WS.10%29.aspx.
  22. How CICS Web support handles pipelining
  23. "Pipelined HTTP Client". http://www.martinbroadhurst.com/Pipelined.html.
  24. http://www.hpl.hp.com/research/linux/httperf/

[edit] External links

  • RFC 2616 Hypertext Transfer Protocol -- HTTP/1.1
  • HTTP/1.1 Pipelining FAQ at mozilla.org
  • "Network Performance Effects of HTTP/1.1, CSS1, and PNG" at w3.org
  • "Optimizing Page Load Times" article
  • phttpget
  • serf C library
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