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Allow passing options to sub protocols
Before this commit we had an issue where configuring a Websocket connection was simply not possible without doing magic, adding callbacks or extra return values. The init/2 function only allowed setting hibernate and timeout options. After this commit, when switching to a different type of handler you can either return {module, Req, State} or {module, Req, State, Opts} where Opts is any value (as far as the sub protocol interface is concerned) and is ultimately checked by the custom handlers. A large protocol like Websocket would accept only a map there, with many different options, while a small interface like loop handlers would allow passing hibernate and nothing else. For Websocket, hibernate must be set from the websocket_init/1 callback, because init/2 executes in a separate process. Sub protocols now have two callbacks: one with the Opts value, one without. The loop handler code was largely reworked and simplified. It does not need to manage a timeout or read from the socket anymore, it's the job of the protocol code. A lot of unnecessary stuff was therefore removed. Websocket compression must now be enabled from the handler options instead of per listener. This means that a project can have two separate Websocket handlers with different options. Compression is still disabled by default, and the idle_timeout value was changed from inifnity to 60000 (60 seconds), as that's safer and is also a good value for mobile devices.
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25 changed files with 171 additions and 244 deletions
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@ -34,7 +34,7 @@ loop handler behavior. This tuple may optionally contain
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a timeout value and/or the atom `hibernate` to make the
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process enter hibernation until a message is received.
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This snippet enables the loop handler.
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This snippet enables the loop handler:
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[source,erlang]
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----
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@ -42,14 +42,12 @@ init(Req, State) ->
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{cowboy_loop, Req, State}.
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----
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However it is largely recommended that you set a timeout
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value. The next example sets a timeout value of 30s and
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also makes the process hibernate.
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This also makes the process hibernate:
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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, 30000, hibernate}.
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{cowboy_loop, Req, State, hibernate}.
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----
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=== Receive loop
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@ -123,25 +121,6 @@ a subsequent request.
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Please refer to the xref:handlers[Handlers chapter]
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for general instructions about cleaning up.
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=== Timeout
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Note that this feature currently does not work. It will be
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brought back in a future 2.0 pre-release.
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By default Cowboy will not attempt to close the connection
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if there is no activity from the client. This is not always
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desirable, which is why you can set a timeout. Cowboy will
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close the connection if no data was received from the client
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after the configured time. The timeout only needs to be set
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once and can't be modified afterwards.
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Because the request may have had a body, or may be followed
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by another request, Cowboy is forced to buffer all data it
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receives. This data may grow to become too large though,
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so there is a configurable limit for it. The default buffer
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size is of 5000 bytes, but it may be changed by setting the
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`loop_max_buffer` middleware environment value.
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=== Hibernate
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To save memory, you may hibernate the process in between
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@ -20,31 +20,31 @@ init(Req, State) ->
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{cowboy_websocket, Req, State}.
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----
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The return value may also have a `Timeout` value and/or the
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atom `hibernate`. These options are useful for long living
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connections. When they are not provided, the timeout value
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defaults to `infinity` and the hibernate value to `run`.
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The returned tuple may also have a fourth element containing
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options for the sub protocol. No option is universal. While
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it will usually be a map of options, it doesn't have to be.
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For example loop handlers accept the atom `hibernate`.
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The following snippet switches to the `my_protocol` sub
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protocol, sets the timeout value to 5 seconds and enables
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hibernation:
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// @todo Yeah maybe what we really need is an Opts map.
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[source,erlang]
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----
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init(Req, State) ->
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{my_protocol, Req, State, 5000, hibernate}.
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{my_protocol, Req, State, #{
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timeout => 5000,
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compress => true}}.
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----
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If a sub protocol does not make use of these options, it should
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crash if it receives anything other than the default values.
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Sub protocols should ignore unknown options so as to not waste
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resources doing unnecessary validation.
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=== Upgrade
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After the `init/2` function returns, Cowboy will then call the
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`upgrade/6` function. This is the only callback defined by the
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`cowboy_sub_protocol` behavior.
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After the `init/2` function returns, Cowboy will call either
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the `upgrade/4` or the `upgrade/5` function. The former is called
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when no options were given; the latter when they were given.
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The function is named `upgrade` because it mimics the mechanism
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of HTTP protocol upgrades. For some sub protocols, like Websocket,
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@ -53,16 +53,19 @@ only an upgrade at Cowboy's level and the client has nothing to
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do about it.
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The upgrade callback receives the Req object, the middleware
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environment, the handler and its options, and the aforementioned
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timeout and hibernate values.
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environment, the handler and its state, and for `upgrade/5`
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also the aformentioned options.
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[source,erlang]
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----
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upgrade(Req, Env, Handler, HandlerOpts, Timeout, Hibernate) ->
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upgrade(Req, Env, Handler, State) ->
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%% Sub protocol code here.
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upgrade(Req, Env, Handler, State, Opts) ->
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%% Sub protocol code here.
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----
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This callback is expected to behave like a middleware and to
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These callbacks are expected to behave like middlewares and to
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return an updated environment and Req object.
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Sub protocols are expected to call the `cowboy_handler:terminate/4`
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@ -60,13 +60,13 @@ be:
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init(Req, State) ->
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case cowboy_req:parse_header(<<"sec-websocket-protocol">>, Req) of
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undefined ->
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{ok, Req, State};
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{cowboy_websocket, Req, State};
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Subprotocols ->
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case lists:keymember(<<"mqtt">>, 1, Subprotocols) of
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true ->
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Req2 = cowboy_req:set_resp_header(<<"sec-websocket-protocol">>,
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<<"mqtt">>, Req),
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{ok, Req2, State};
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{cowboy_websocket, Req2, State};
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false ->
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{stop, Req, State}
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end
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@ -210,12 +210,13 @@ than needed.
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The `init/2` callback can set the timeout to be used
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for the connection. For example, this would make Cowboy
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close connections idle for more than 60 seconds:
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close connections idle for more than 30 seconds:
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[source,erlang]
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----
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init(Req, State) ->
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{cowboy_websocket, Req, State, 60000}.
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{cowboy_websocket, Req, State, #{
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idle_timeout => 30000}}.
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----
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This value cannot be changed once it is set. It defaults to
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@ -65,6 +65,5 @@ Cowboy's Websocket implementation also includes the
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permessage-deflate and x-webkit-deflate-frame compression
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extensions.
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Cowboy will automatically use compression as long as the
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`websocket_compress` protocol option is set when starting
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the listener.
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Cowboy will automatically use compression when the
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`compress` option is returned from the `init/2` function.
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