From a45813c60f0f983a24ea29d491b37f0590fdd087 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= Date: Sat, 18 Feb 2017 18:26:20 +0100 Subject: 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. --- doc/src/guide/loop_handlers.asciidoc | 27 +++------------------------ doc/src/guide/sub_protocols.asciidoc | 35 +++++++++++++++++++---------------- doc/src/guide/ws_handlers.asciidoc | 9 +++++---- doc/src/guide/ws_protocol.asciidoc | 5 ++--- 4 files changed, 29 insertions(+), 47 deletions(-) (limited to 'doc/src/guide') diff --git a/doc/src/guide/loop_handlers.asciidoc b/doc/src/guide/loop_handlers.asciidoc index 2c82c53..dbee927 100644 --- a/doc/src/guide/loop_handlers.asciidoc +++ b/doc/src/guide/loop_handlers.asciidoc @@ -34,7 +34,7 @@ loop handler behavior. This tuple may optionally contain a timeout value and/or the atom `hibernate` to make the process enter hibernation until a message is received. -This snippet enables the loop handler. +This snippet enables the loop handler: [source,erlang] ---- @@ -42,14 +42,12 @@ init(Req, State) -> {cowboy_loop, Req, State}. ---- -However it is largely recommended that you set a timeout -value. The next example sets a timeout value of 30s and -also makes the process hibernate. +This also makes the process hibernate: [source,erlang] ---- init(Req, State) -> - {cowboy_loop, Req, State, 30000, hibernate}. + {cowboy_loop, Req, State, hibernate}. ---- === Receive loop @@ -123,25 +121,6 @@ a subsequent request. Please refer to the xref:handlers[Handlers chapter] for general instructions about cleaning up. -=== Timeout - -Note that this feature currently does not work. It will be -brought back in a future 2.0 pre-release. - -By default Cowboy will not attempt to close the connection -if there is no activity from the client. This is not always -desirable, which is why you can set a timeout. Cowboy will -close the connection if no data was received from the client -after the configured time. The timeout only needs to be set -once and can't be modified afterwards. - -Because the request may have had a body, or may be followed -by another request, Cowboy is forced to buffer all data it -receives. This data may grow to become too large though, -so there is a configurable limit for it. The default buffer -size is of 5000 bytes, but it may be changed by setting the -`loop_max_buffer` middleware environment value. - === Hibernate To save memory, you may hibernate the process in between diff --git a/doc/src/guide/sub_protocols.asciidoc b/doc/src/guide/sub_protocols.asciidoc index 2ab96bc..83fa975 100644 --- a/doc/src/guide/sub_protocols.asciidoc +++ b/doc/src/guide/sub_protocols.asciidoc @@ -20,31 +20,31 @@ init(Req, State) -> {cowboy_websocket, Req, State}. ---- -The return value may also have a `Timeout` value and/or the -atom `hibernate`. These options are useful for long living -connections. When they are not provided, the timeout value -defaults to `infinity` and the hibernate value to `run`. +The returned tuple may also have a fourth element containing +options for the sub protocol. No option is universal. While +it will usually be a map of options, it doesn't have to be. +For example loop handlers accept the atom `hibernate`. The following snippet switches to the `my_protocol` sub protocol, sets the timeout value to 5 seconds and enables hibernation: -// @todo Yeah maybe what we really need is an Opts map. - [source,erlang] ---- init(Req, State) -> - {my_protocol, Req, State, 5000, hibernate}. + {my_protocol, Req, State, #{ + timeout => 5000, + compress => true}}. ---- -If a sub protocol does not make use of these options, it should -crash if it receives anything other than the default values. +Sub protocols should ignore unknown options so as to not waste +resources doing unnecessary validation. === Upgrade -After the `init/2` function returns, Cowboy will then call the -`upgrade/6` function. This is the only callback defined by the -`cowboy_sub_protocol` behavior. +After the `init/2` function returns, Cowboy will call either +the `upgrade/4` or the `upgrade/5` function. The former is called +when no options were given; the latter when they were given. The function is named `upgrade` because it mimics the mechanism of HTTP protocol upgrades. For some sub protocols, like Websocket, @@ -53,16 +53,19 @@ only an upgrade at Cowboy's level and the client has nothing to do about it. The upgrade callback receives the Req object, the middleware -environment, the handler and its options, and the aforementioned -timeout and hibernate values. +environment, the handler and its state, and for `upgrade/5` +also the aformentioned options. [source,erlang] ---- -upgrade(Req, Env, Handler, HandlerOpts, Timeout, Hibernate) -> +upgrade(Req, Env, Handler, State) -> + %% Sub protocol code here. + +upgrade(Req, Env, Handler, State, Opts) -> %% Sub protocol code here. ---- -This callback is expected to behave like a middleware and to +These callbacks are expected to behave like middlewares and to return an updated environment and Req object. Sub protocols are expected to call the `cowboy_handler:terminate/4` diff --git a/doc/src/guide/ws_handlers.asciidoc b/doc/src/guide/ws_handlers.asciidoc index 011aa31..2c38b87 100644 --- a/doc/src/guide/ws_handlers.asciidoc +++ b/doc/src/guide/ws_handlers.asciidoc @@ -60,13 +60,13 @@ be: init(Req, State) -> case cowboy_req:parse_header(<<"sec-websocket-protocol">>, Req) of undefined -> - {ok, Req, State}; + {cowboy_websocket, Req, State}; Subprotocols -> case lists:keymember(<<"mqtt">>, 1, Subprotocols) of true -> Req2 = cowboy_req:set_resp_header(<<"sec-websocket-protocol">>, <<"mqtt">>, Req), - {ok, Req2, State}; + {cowboy_websocket, Req2, State}; false -> {stop, Req, State} end @@ -210,12 +210,13 @@ than needed. The `init/2` callback can set the timeout to be used for the connection. For example, this would make Cowboy -close connections idle for more than 60 seconds: +close connections idle for more than 30 seconds: [source,erlang] ---- init(Req, State) -> - {cowboy_websocket, Req, State, 60000}. + {cowboy_websocket, Req, State, #{ + idle_timeout => 30000}}. ---- This value cannot be changed once it is set. It defaults to diff --git a/doc/src/guide/ws_protocol.asciidoc b/doc/src/guide/ws_protocol.asciidoc index 127c829..8fa0673 100644 --- a/doc/src/guide/ws_protocol.asciidoc +++ b/doc/src/guide/ws_protocol.asciidoc @@ -65,6 +65,5 @@ Cowboy's Websocket implementation also includes the permessage-deflate and x-webkit-deflate-frame compression extensions. -Cowboy will automatically use compression as long as the -`websocket_compress` protocol option is set when starting -the listener. +Cowboy will automatically use compression when the +`compress` option is returned from the `init/2` function. -- cgit v1.2.3