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- ::: The Websocket protocol
- This chapter explains what Websocket is and why it is
- a vital component of soft realtime Web applications.
- :: Description
- Websocket is an extension to HTTP that emulates plain TCP
- connections between the client, typically a Web browser,
- and the server. It uses the HTTP Upgrade mechanism to
- establish the connection.
- Websocket connections are asynchronous, unlike HTTP. This
- means that not only can the client send frames to the server
- at any time, but the server can also send frames to the client
- without the client initiating anything other than the
- Websocket connection itself. This allows the server to push
- data to the client directly.
- Websocket is an IETF standard. Cowboy supports the standard
- and all drafts that were previously implemented by browsers,
- excluding the initial flawed draft sometimes known as
- "version 0".
- :: Implementation
- Cowboy implements Websocket as a protocol upgrade. Once the
- upgrade is performed from the `init/2` callback, Cowboy
- switches to Websocket. Please consult the next chapter for
- more information on initiating and handling Websocket
- connections.
- The implementation of Websocket in Cowboy is validated using
- the Autobahn test suite, which is an extensive suite of tests
- covering all aspects of the protocol. Cowboy passes the
- suite with 100% success, including all optional tests.
- Cowboy's Websocket implementation also includes the
- x-webkit-deflate-frame compression draft which is being used
- by some browsers to reduce the size of data being transmitted.
- Cowboy will automatically use compression as long as the
- `compress` protocol option is set when starting the listener.
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