From 4023e7f4e429179fd9c2cce4487c33646c6bd327 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= Date: Thu, 14 Jan 2016 13:35:25 +0100 Subject: Convert the documentation to Asciidoc A few small revisions were made, and Erlang.mk has been updated. --- doc/src/guide/ws_handlers.ezdoc | 188 ---------------------------------------- 1 file changed, 188 deletions(-) delete mode 100644 doc/src/guide/ws_handlers.ezdoc (limited to 'doc/src/guide/ws_handlers.ezdoc') diff --git a/doc/src/guide/ws_handlers.ezdoc b/doc/src/guide/ws_handlers.ezdoc deleted file mode 100644 index a0cfc29..0000000 --- a/doc/src/guide/ws_handlers.ezdoc +++ /dev/null @@ -1,188 +0,0 @@ -::: Handling Websocket connections - -A special handler is required for handling Websocket connections. -Websocket handlers allow you to initialize the connection, -handle incoming frames from the socket, handle incoming Erlang -messages and then clean up on termination. - -Websocket handlers essentially act as a bridge between the client -and the Erlang system. They will typically do little more than -socket communication and decoding/encoding of frames. - -:: Initialization - -First, the `init/2` callback is called. This callback is common -to all handlers. To establish a Websocket connection, this function -must return a `ws` tuple. - -``` erlang -init(Req, _Opts) -> - {cowboy_websocket, Req, #state{}}. -``` - -Upon receiving this tuple, Cowboy will switch to the code -that handles Websocket connections and perform the handshake -immediately. - -If the sec-websocket-protocol header was sent with the request -for establishing a Websocket connection, then the Websocket -handler *must* select one of these subprotocol and send it -back to the client, otherwise the client might decide to close -the connection, assuming no correct subprotocol was found. - -``` erlang -init(Req, _Opts) -> - case cowboy_req:parse_header(<<"sec-websocket-protocol">>, Req) of - undefined -> - {ok, Req, #state{}}; - Subprotocols -> - case lists:keymember(<<"mychat2">>, 1, Subprotocols) of - true -> - Req2 = cowboy_req:set_resp_header(<<"sec-websocket-protocol">>, - <<"mychat2">>, Req), - {ok, Req2, #state{}}; - false -> - {stop, Req, undefined} - end - end. -``` - -It is not recommended to wait too long inside the `init/2` -function. Any extra initialization may be done after returning by -sending yourself a message before doing anything. Any message sent -to `self()` from `init/2` is guaranteed to arrive before -any frames from the client. - -It is also very easy to ensure that this message arrives before -any message from other processes by sending it before registering -or enabling timers. - -``` erlang -init(Req, _Opts) -> - self() ! post_init, - %% Register process here... - {cowboy_websocket, Req, #state{}}. - -websocket_info(post_init, Req, State) -> - %% Perform post_init initialization here... - {ok, Req, State}. -``` - -:: Handling frames from the client - -Cowboy will call `websocket_handle/3` whenever a text, binary, -ping or pong frame arrives from the client. Note that in the -case of ping and pong frames, no action is expected as Cowboy -automatically replies to ping frames. - -The handler can decide to send frames to the socket, stop -or just continue without sending anything. - -The following snippet echoes back any text frame received and -ignores all others. - -``` erlang -websocket_handle(Frame = {text, _}, Req, State) -> - {reply, Frame, Req, State}; -websocket_handle(_Frame, Req, State) -> - {ok, Req, State}. -``` - -:: Handling Erlang messages - -Cowboy will call `websocket_info/3` whenever an Erlang message -arrives. - -The handler can decide to send frames to the socket, stop -or just continue without sending anything. - -The following snippet forwards any `log` message to the socket -and ignores all others. - -``` erlang -websocket_info({log, Text}, Req, State) -> - {reply, {text, Text}, Req, State}; -websocket_info(_Info, Req, State) -> - {ok, Req, State}. -``` - -:: Sending frames to the socket - -Cowboy allows sending either a single frame or a list of -frames to the socket, in which case the frames are sent -sequentially. Any frame can be sent: text, binary, ping, -pong or close frames. - -The following example sends three frames using a single `reply` -tuple. - -``` erlang -websocket_info(hello_world, Req, State) -> - {reply, [ - {text, "Hello"}, - {text, <<"world!">>}, - {binary, <<0:8000>>} - ], Req, State}; -%% More websocket_info/3 clauses here... -``` - -Note that the payload for text and binary frames is of type -`iodata()`, meaning it can be either a `binary()` or an -`iolist()`. - -Sending a `close` frame will immediately initiate the closing -of the Websocket connection. Be aware that any additional -frames sent by the client or any Erlang messages waiting to -be received will not be processed. Also note that when replying -a list of frames that includes close, any frame found after the -close frame will not be sent. - -:: Ping and timeout - -The biggest performance improvement you can do when dealing -with a huge number of Websocket connections is to reduce the -number of timers that are started on the server. A common use -of timers when dealing with connections is for sending a ping -every once in a while. This should be done exclusively on the -client side. Indeed, a server handling one million Websocket -connections will perform a lot better when it doesn't have to -handle one million extra timers too! - -Cowboy will automatically respond to ping frames sent by the -client. It will still forward the frame to the handler for -informative purpose, but no further action is required. - -Cowboy can be configured to automatically close the Websocket -connection when no data arrives on the socket. It is highly -recommended to configure a timeout for it, as otherwise you -may end up with zombie "half-connected" sockets that may -leave the process alive forever. - -A good timeout value is 60 seconds. - -``` erlang -init(Req, _Opts) -> - {cowboy_websocket, Req, #state{}, 60000}. -``` - -This value cannot be changed once it is set. It defaults to -`infinity`. - -:: Hibernate - -Most tuples returned from handler callbacks can include an -extra value `hibernate`. After doing any necessary operations -following the return of the callback, Cowboy will hibernate -the process. - -It is highly recommended to hibernate processes that do not -handle much traffic. It is a good idea to hibernate all -connections by default and investigate only when you start -noticing increased CPU usage. - -:: Supporting older browsers - -Unfortunately Websocket is a relatively recent technology, -which means that not all browsers support it. A library like -^"Bullet^https://github.com/extend/bullet^ can be used to -emulate Websocket connections on older browsers. -- cgit v1.2.3