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{{short description|Web application model}}
'''Comet''' is a [[web application]] model in which a long-held [[HTTPS]] request allows a [[web server]] to [[Push technology|push]] data to a [[web browser|browser]], without the browser explicitly requesting it.<ref name='"MASH'">{{cite web | url = http://www.infoworld.com/d/developer-world/ajax-alliance-recognizes-mashups-559 | title = AJAX alliance recognizes mashups | access-date = 2010-10-20 | last = Krill | first = Paul | date = September 24, 2007 | publisher = [[InfoWorld]]}}</ref><ref name="CRANG">{{cite book|title=Comet and Reverse Ajax: The Next-Generation Ajax 2.0|last2=McCarthy|first2=Phil|date=October 13, 2008|publisher=[[Apress]]|isbn=978-1-59059-998-3|last1=Crane|first1=Dave}}<!--| accessdate = 2010-10-20 --></ref> ''Comet'' is an [[umbrella term]], encompassing multiple techniques for achieving this interaction. All these methods rely on features included by default in browsers, such as [[JavaScript]], rather than on non-default plugins. The Comet approach differs from the [[World Wide Web#Function|original model of the web]], in which a browser requests a complete web page at a time.<ref name = "WRC" />
 
The use of Comet techniques in [[web development]] predates the use of the word ''Comet'' as a [[neologism]] for the collective techniques. Comet is known by several other names, including
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|author2=McCarthy, Phil
|publisher = Apress
|isbn = 978-1-59059-998-53
|date=July 2008
}}</ref> ''Two-way-web'',<ref name="ajax-dp-oreilly"/> ''HTTP Streaming'',<ref name="ajax-dp-oreilly">{{cite book
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|pages=[https://archive.org/details/ajaxdesignpatter00mahe/page/19 19; 85]
|chapter=Web Remoting
|chapter-url-access=registration
|chapter-url=https://archive.org/details/ajaxdesignpatter00mahe/page/19
}}</ref> and
''[[HTTP push|HTTP server push]]''<ref>{{cite web
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|archive-date = 2006-02-08
}}
</ref> The term ''Comet'' is not an acronym, but was coined by Alex Russell in his 2006 [[blog]] post.{{efn|<ref>{{cite web
|url = http://infrequently.org/2006/03/comet-low-latency-data-for-the-browser/
|title = Comet: Low Latency Data for the Browser
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|last = Russell
|date = 2006-03-04
|access-date = 2014-11-02}}
}}</ref>{{source?citation needed|date=June 2023}}
 
In recent years{{When|date=January 2025}}, the standardisation and widespread support of [[WebSocket]] and [[Server-sent events]] has rendered the Comet model obsolete.
 
==History==
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| publisher = Northeast Parallel Architecture Center, College of Engineering and Computer Science
| access-date = 27 February 2016
}}</ref>{{failed verification|date=December 2017}} implemented in 1996–98 at the Northeast Parallel Architectures Center ([http://surface.syr.edu/npac/ NPAC]) at [[Syracuse University]] using [[DARPA]] funding. TANGO architecture has been patented by Syracuse University.<ref>{{Citation|lastlast1 = Podgorny|firstfirst1 = Marek|title = United States Patent: 6078948 - Platform-independent collaboration backbone and framework for forming virtual communities having virtual rooms with collaborative sessions|date = June 20, 2000|url = http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%252Fnetahtml%252FPTO%252Fsearch-bool.html&r=14&f=G&l=50&co1=AND&d=PTXT&s1=Podgorny.INNM.&OS=IN/Podgorny&RS=IN/Podgorny|last2 = Beca|last3 = Cheng|last4 = Fox|last5 = Jurga|last6 = Olszewski|last7 = Sokolowski|last8 = Walczak|last9 = PL|first2 = Lukasz|first3 = Gang|first4 = Geoffrey C.|first5 = Tomasz|first6 = Konrad|first7 = Piotr|first8 = Krzysztof|access-date = 2016-02-27|archive-date = 2017-05-09|archive-url = https://web.archive.org/web/20170509022914/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%252Fnetahtml%252FPTO%252Fsearch-bool.html&r=14&f=G&l=50&co1=AND&d=PTXT&s1=Podgorny.INNM.&OS=IN/Podgorny&RS=IN/Podgorny|url-status = dead}}</ref> TANGO framework has been extensively used as a distance education tool.<ref>{{Cite web
| url = https://www.dsc.soic.indiana.edu/sites/default/files/tr_9921.pdf
| title = Experiences with Using TANGO Interactive in a Distributed Workshop
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| archive-url = https://web.archive.org/web/20210308093626/https://www.dsc.soic.indiana.edu/sites/default/files/tr_9921.pdf
| url-status = dead
}}</ref> The framework has been commercialized by [http://www.collabworx.com CollabWorx] and used in a dozen or so Command&Control and Training applications in the United States Department of Defense{{factcitation needed|date=December 2017}}.
 
===First Comet applications===
The first set of Comet implementations dates back to 2000,<ref name="CometDaily_History">{{cite web |url=http://cometdaily.com/2007/10/19/comet-and-push-technology/ |title=CometDaily: Comet and Push Technology |access-date=2007-12-15 |archive-url=https://web.archive.org/web/20071113174053/http://cometdaily.com/2007/10/19/comet-and-push-technology/ |archive-date=2007-11-13 |url-status=dead }}</ref>{{unreliable source?|date=November 2017}} with the [[Pushlets]], [[Lightstreamer]], and KnowNow projects. [[Pushlets]], a framework created by Just van den Broecke, was one of the first<ref name="pushlets-javaworld">Just van den Broecke (1 March 2000). “[http://www.javaworld.com/article/2076063/java-web-development/pushlets--send-events-from-servlets-to-dhtml-client-browsers.html Pushlets: Send events from servlets to DHTML client browsers] {{Webarchive|url=https://web.archive.org/web/20140804175811/http://www.javaworld.com/article/2076063/java-web-development/pushlets--send-events-from-servlets-to-dhtml-client-browsers.html |date=2014-08-04 }}”. JavaWorld. Retrieved 1 August 2014.</ref> open source implementations. Pushlets were based on server-side Java servlets, and a client-side JavaScript library. Bang Networks{{snd}} a [[Silicon Valley]] start-up backed by [[Netscape]] co-founder [[Marc Andreessen]]{{snd}} had a lavishly- financed attempt to create a real-time push standard for the entire web.<ref>{{cite web
|url=http://news.cnet.com/2100-1023-255088.html
|title=Will the "refresh" button become obsolete?
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| publisher = [[O'Reilly Media]]
|date=January 2008
| isbn = 978-0-596-52838-86
| chapter = Page Layout with Frames that Aren't
| page = 320
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|url=https://archive.org/details/javascript00libg_297
|url-access=registration
|series=The Definitive Guide
|date=2006-08-17
|publisher=[[O'Reilly Media]]
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Browser-native technologies are inherent in the term Comet. Attempts to improve non-polling HTTP communication have come from multiple sides:
 
* The [[HTML 5]] draft specification produced by the [[Web Hypertext Application Technology Working Group]] (WHATWG) specifies so called [[server-sent events]],<ref name='"server-sent-events'">{{cite web|editor=Ian Hickson |date=2007-10-27 |work=HTML 5 - Call For Comments|title=6.2 Server-sent DOM events|url=http://www.whatwg.org/specs/web-apps/2007-10-26/multipage/section-server-sent-events.html#server-sent-events |publisher=[[WHATWG]]|access-date=2008-10-07}}</ref> which defines a new JavaScript interface <code>EventSource</code> and a new MIME type <code>text/event-stream</code>. [[Server-sent_events#Web_browsers|All major browsers except Microsoft Internet Explorer]] include this technology.
* The [[HTML 5]] [[WebSocket]] API working draft specifies a method for creating a persistent connection with a server and receiving messages via an <code>onmessage</code> callback.<ref>
{{cite web
|url=http://www.w3.org/TR/websockets/
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}}</ref>
* Use of plugins, such as [[Java applet]]s or the proprietary [[Adobe Flash]] (using [[Real-Time Messaging Protocol|RTMP]] protocol for data streaming to Flash applications). These have the advantage of working identically across all browsers with the appropriate plugin installed and need not rely on HTTP connections, but the disadvantage of requiring the plugin to be installed
* [[Google]] announced<ref>App, The. (2010-12-02) [httphttps://googleappengine.blogspot.com/2010/12/happy-holidays-from-app-engine-team-140.html Google App Engine Blog: Happy Holidays from the App Engine team - 1.4.0 SDK released]. Googleappengine.blogspot.com. Retrieved on 2014-04-12.</ref> a new Channel API for [[Google App Engine]],<ref>Paul, Ryan. (2010-12-06) [https://arstechnica.com/web/news/2010/12/app-engine-gets-streaming-api-and-longer-background-tasks.ars App Engine gets Streaming API and longer background tasks]. Ars Technica. Retrieved on 2014-04-12.</ref> implementing a Comet-like API with the help of a client JavaScript library on the browser. This API has been deprecated. <ref>{{cite web |url=https://cloud.google.com/appengine/docs/standard/java/javadoc/com/google/appengine/api/channel/package-summary |title=Package com.google.appengine.api.channel |publisher=[[Google]] |date=2019-11-16 |access-date=2020-04-30 |quote=This API has been deprecated. }}</ref>
 
==See also==
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== Notes ==
{{noteslistnotelist}}
 
==References==