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Update the Websocket protocol chapter

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Loïc Hoguin 2016-09-01 17:42:41 +02:00
parent 5495b57174
commit 67c5b057f9
1 changed files with 36 additions and 9 deletions
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45
doc/src/guide/ws_protocol.asciidoc
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@ -11,18 +11,43 @@ connections between the client, typically a Web browser,
and the server. It uses the HTTP Upgrade mechanism to and the server. It uses the HTTP Upgrade mechanism to
establish the connection. establish the connection.
Websocket connections are asynchronous, unlike HTTP. This Websocket connections are fully asynchronous, unlike
means that not only can the client send frames to the server HTTP/1.1 (synchronous) and HTTP/2 (asynchronous, but the
at any time, but the server can also send frames to the client server can only initiate streams in response to requests).
without the client initiating anything other than the With Websocket, the client and the server can both send
Websocket connection itself. This allows the server to push frames at any time without any restriction. It is closer
data to the client directly. to TCP than any of the HTTP protocols.
Websocket is an IETF standard. Cowboy supports the standard Websocket is an IETF standard. Cowboy supports the standard
and all drafts that were previously implemented by browsers, and all drafts that were previously implemented by browsers,
excluding the initial flawed draft sometimes known as excluding the initial flawed draft sometimes known as
"version 0". "version 0".
=== Websocket vs HTTP/2
For a few years Websocket was the only way to have a
bidirectional asynchronous connection with the server.
This changed when HTTP/2 was introduced. While HTTP/2
requires the client to first perform a request before
the server can push data, this is only a minor restriction
as the client can do so just as it connects.
Websocket was designed as a kind-of-TCP channel to a
server. It only defines the framing and connection
management and lets the developer implement a protocol
on top of it. For example you could implement IRC over
Websocket and use a Javascript IRC client to speak to
the server.
HTTP/2 on the other hand is just an improvement over
the HTTP/1.1 connection and request/response mechanism.
It has the same semantics as HTTP/1.1.
If all you need is to access an HTTP API, then HTTP/2
should be your first choice. On the other hand, if what
you need is a different protocol, then you can use
Websocket to implement it.
=== Implementation === Implementation
Cowboy implements Websocket as a protocol upgrade. Once the Cowboy implements Websocket as a protocol upgrade. Once the
@ -37,7 +62,9 @@ covering all aspects of the protocol. Cowboy passes the
suite with 100% success, including all optional tests. suite with 100% success, including all optional tests.
Cowboy's Websocket implementation also includes the Cowboy's Websocket implementation also includes the
x-webkit-deflate-frame compression draft which is being used permessage-deflate and x-webkit-deflate-frame compression
by some browsers to reduce the size of data being transmitted. extensions.
Cowboy will automatically use compression as long as the Cowboy will automatically use compression as long as the
`compress` protocol option is set when starting the listener. `websocket_compress` protocol option is set when starting
the listener.