How to enable active sockets in a Mochiweb application?

Question

Does anyone know how to enable active instead of passive sockets in a Mochiweb application. Specifically, I am trying to adapt http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-2 so that when a client disconnects, it will immediately "logout".

I have tried setting:

start(Options) ->
    {DocRoot, Options1} = get_option(docroot, Options),
    Loop = fun (Req) ->
        Socket = Req:get(socket),
        inet:setopts(Socket, [{active, once}]),
        ?MODULE:loop(Req, DocRoot)
    end,

but that seems to not be working. I still only get updates in my receive after I am sent a new message.

Thoughts? Thanks!

Answer 1

I solved this for my Erlang comet app, parts of which I show in this blog post. Basically, you don't want the socket to be in active mode all the time; you just want it in active mode after you've read the client's request and before you return a response.

Here's a sample request handler:

comet(Req) ->
    Body = Req:recv_body(),
    io:format("~nBody: ~p~n", [Body]),
    Socket = Req:get(socket),
    inet:setopts(Socket, [{active, once}]),
    Response = connection:handle_json(Body),
    inet:setopts(Socket, [{active, false}]),
    io:format("~nSending Response: ~s~n", [Response]),
    Req:ok({"application/json", [], Response}).

The io:format call is just console logging for my benefit. The important part is that I set {active, once} on the socket after reading the body from the request and just before calling the function which holds the request and returns data. I also turn active mode back off; the socket may be reused in certain HTTP modes.