Web Sockets For Elli!

This was done during HackNashville with little sleep and lots of caffeine (it's good for you). There are things missing.

Use

To use this, you'll have to add the middleware to Elli and implement a websocket behavior.

Add The Middleware

Here is an example of how I configure this along with the static file middleware in a supervisor:

-module(frenetic_sup).
-behaviour(supervisor).
-export([start_link/0, init/1]).

-define(SERVER, ?MODULE).

start_link() ->
	supervisor:start_link({local, ?SERVER}, ?MODULE, []).

init([]) ->
	RestartStrategy = one_for_one,
	MaxRestarts = 3,
	MaxSecondsBetweenRestarts = 60,

	SupFlags = {RestartStrategy, MaxRestarts, MaxSecondsBetweenRestarts},

	FileserveConfig = [{prefix, <<"/public">>},
					   {path, <<"./public">>}],

	WSConfig = [{path, <<"/websocket">>},
				{websocket, my_websocket_behavior}],

	MWConfig = [{mods, [
			{elli_fileserve, FileserveConfig},
			{elli_websocket, WSConfig}
		]}],
	ElliOpts = [{callback, elli_middleware}, {port, 8090}, {callback_args,MWConfig}],

	Elli = create_child_spec(elli, worker, permanent, 1000, [ElliOpts]),
	
	{ok, {SupFlags, [Elli]}}.

create_child_spec(Child, Type, Restart, Shutdown, Args) ->
	{Child, { Child, start_link, Args }, Restart, Shutdown, Type, [Child]}.

Create Your WebSocket Behavior

This is a silly behavior implementation. I suggest maybe making this also implement a gen_server or something that can track the sockets over time. You must provide an identifier for the socket which will be used to identify which socket you are receiving data/events from.

%%% the saddest websocket behavior that ever was...
-module(my_websocket).
-behavior(websocket).
-export([handle_client/2, handle_close/1, handle_message/2, handle_ready/2]).

%% exists to provide a unique socket identifier based on request headers
handle_client(Headers) ->
	SendCallback("Hi, new websocket client!"),
	new_id. %% you want this to be unique per socket

%% called when the socket is closed for any reason
%% Reason :: socket_closed | client_signal | protocol_error
handle_close(Id, Reason) -> io:format("Websocket ~p closed. Reason: ~p.~n", [Id, Reason]).

%% handles incoming messages
handle_message(Id, Message) -> io:format("~p : ~p ~n", [Id, Message]).

%% once the socket is ready, you get a fun/1 for sending messages to that socket
%% the id is provided so that you can store the callback for that particular socket
handle_ready(Id, Send) -> Send("hello, world!").

Install

Add the following to your rebar.config in the {deps,[]} collection:

	{elli, "",
		{git, "git://github.com/knutin/elli",
		{branch, "master" } } },
	{elli_websockets, "",
        {git, "git://github.com/arobson/elli_websockets",
        {branch, "master" } } }

TO DO

* add support for hixie protocols
* provide a better example websocket behavior
* tests?