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40 lines
1.1 KiB
Markdown
40 lines
1.1 KiB
Markdown
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Handlers
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========
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Purpose
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-------
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Handlers are Erlang modules that represent a resource.
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Handlers must process the request and send a reply. The nature of the
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reply will vary between handlers.
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Different kinds of handlers can be combined in a single module. This
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allows a module to handle both websocket and long-polling code in a
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single place, for example.
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Protocol upgrades
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-----------------
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Cowboy features many different handlers: HTTP handlers, loop handlers,
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websocket handlers, REST handlers and static handlers. All of them
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have a common entry point: the `init/3` function.
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By default, Cowboy considers your handler to be an HTTP handler.
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To switch to a different protocol, like, for example, Websocket,
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you must perform a protocol upgrade. This is done by returning
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a protocol upgrade tuple at the end of `init/3`.
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The following snippet upgrades the handler to `my_protocol`.
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``` erlang
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init(_Any, _Req, _Opts) ->
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{upgrade, protocol, my_protocol}.
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```
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The `my_protocol` module will be used for further processing of the
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request. It requires only one callback, `upgrade/4`.
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@todo Describe `upgrade/4` when the middleware code gets pushed.
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