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= cowboy_loop(3)
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== Name
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2016-12-23 17:20:54 +01:00
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cowboy_loop - Loop handlers
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== Description
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The module `cowboy_loop` defines a callback interface for
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long running HTTP connections.
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2016-12-23 17:20:54 +01:00
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You should switch to this behavior for long polling,
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server-sent events and similar long-running requests.
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2016-12-23 17:20:54 +01:00
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There are generally two usage patterns:
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* Loop until receiving a specific message, then send
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a response and stop execution (for example long polling);
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* Or initiate a response in `init/2` and stream the
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body in `info/3` as necessary (for example server-sent events).
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2016-12-23 17:20:54 +01:00
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== Callbacks
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2016-12-23 17:20:54 +01:00
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Loop handlers implement the following interface:
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2016-12-23 17:20:54 +01:00
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[source,erlang]
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----
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init(Req, State)
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-> {cowboy_loop, Req, State}
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| {cowboy_loop, Req, State, hibernate}
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| {cowboy_loop, Req, State, timeout()}
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| {cowboy_loop, Req, State, timeout(), hibernate}
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info(Info, Req, State)
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-> {ok, Req, State}
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| {ok, Req, State, hibernate}
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| {stop, Req, State}
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terminate(Reason, Req, State) -> ok %% optional
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Req :: cowboy_req:req()
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State :: any()
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Info :: any()
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Reason :: stop | timeout
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| {crash, error | exit | throw, any()}
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----
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The `init/2` callback is common to all handlers. To switch
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to the loop behavior, it must return `cowboy_loop` as the
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first element of the tuple.
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The `info/3` callback will be called for every Erlang message
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received. It may choose to continue the receive loop or stop
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it.
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The optional `terminate/3` callback will ultimately be called
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with the reason for the termination of the handler.
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Cowboy will terminate the process right after this. There
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is no need to perform any cleanup in this callback.
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2016-12-23 17:20:54 +01:00
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The following terminate reasons are defined for loop handlers:
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stop::
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The handler requested to close the connection by returning
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a `stop` tuple.
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timeout::
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The connection has been closed due to inactivity. The timeout
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value can be configured from `init/2`. The response sent when
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this happens is a `204 No Content`.
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{crash, Class, Reason}::
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A crash occurred in the handler. `Class` and `Reason` can be
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used to obtain more information about the crash. The function
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`erlang:get_stacktrace/0` can also be called to obtain the
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stacktrace of the process when the crash occurred.
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//{error, overflow}::
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// The connection is being closed and the process terminated
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// because the buffer Cowboy uses to keep data sent by the
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// client has reached its maximum. The buffer size can be
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// configured through the environment value `loop_max_buffer`
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// and defaults to 5000 bytes.
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// +
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// If the long running request comes with a body it is recommended
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// to process this body before switching to the loop sub protocol.
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//
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//{error, closed}::
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// The socket has been closed brutally without a close frame being
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// received first.
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//
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//{error, Reason}::
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// A socket error ocurred.
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== Changelog
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* *2.0*: Cowboy temporarily no longer checks the socket for data with HTTP/1.1.
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* *1.0*: Behavior introduced.
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== See also
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link:man:cowboy(7)[cowboy(7)],
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link:man:cowboy_handler(3)[cowboy_handler(3)]
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