[erlang-questions] Push a message to cowboy websockets

Loïc Hoguin <>
Fri Mar 16 21:18:12 CET 2012


Did you start gproc? application:start(gproc)

On 03/16/2012 09:05 PM, AD wrote:
> Thanks, getting some stacktraces though...
>
> ** Handler ad_test terminating in websocket_init/3
>     for the reason error:badarg
>
> i have
>
> /-define(WSBroadcast,"wsbroadcast")./
>
> then in websocket_init
>
> /gproc:reg({p, l, {?MODULE, ?WSBroadcast}})/
> /
> /
> then in my handle() method in cowboy for a certain path
>
> /{URLPath,_Req2} = cowboy_http_req:path(Req),/
> /    case lists:nth(1,URLPath) of/
> /<<"sendit">> -> /
> /%io:format("Sending websocket !!~n"),/
> /Msg = "Test broadcast",/
> /gproc:send({p, l, {?MODULE,?WSBroadcast}}, {self(),
> {?MODULE,?WSBroadcast}, Msg});/
> /
> /
> then in websocket_info
>
> w/ebsocket_info({_PID,{_MODULE,_WSBroadcast},Msg},Req,State) ->/
> /{reply, {text, <<Msg>>}, Req, State, hibernate}./
>
> Any thoughts ?  Looks like something with ets:insert
>
> ** Stacktrace: [{ets,insert_new,
>                      [gproc,
>                       [{{{p,l,{ad_test,"wsbroadcast"}},<0.153.0>},
> <0.153.0>,undefined},
>                        {{<0.153.0>,{p,l,{ad_test,"wsbroadcast"}}},[]}]],
>                      []},
>
> Thanks again for the help
> -AD
>
> On Fri, Mar 16, 2012 at 2:06 PM, Loïc Hoguin <
> <mailto:>> wrote:
>
>     Just like you would catch any message, you match:
>
>     websocket_info({Pid, {Module, WSBroadcast}, Msg}, Req, State)
>
>     When using gproc:send/2, the second arg is what you want to match in
>     the first arg of websocket_info/3. All messages the websocket
>     process receives are given to you in websocket_info/3.
>
>     Didn't try the new pubsub, it looks interesting though.
>
>
>     On 03/16/2012 07:01 PM, AD wrote:
>
>         Thanks, so in websocket/init
>
>         gproc:reg({p, l, {?MODULE, WSBroadcast}}).
>
>         Then in my webservice i can do
>
>         Msg = "Test broadcast".
>         gproc:send({p, l, {?MODULE,WSBroadcast}}, {self(),
>         {?MODULE,WSBroadcast}, Msg}).
>
>         How do you catch this in websocket_info/3 to formulate a reply?
>
>         Also noticed a new pub/sub module for gproc not sure if this helps
>         simplify some of this
>         https://github.com/uwiger/__gproc/blob/master/src/gproc___ps.erl
>         <https://github.com/uwiger/gproc/blob/master/src/gproc_ps.erl>
>
>         Thanks!
>         -AD
>
>         On Fri, Mar 16, 2012 at 12:20 PM, Loïc Hoguin
>         < <mailto:>
>         <mailto: <mailto:>>> wrote:
>
>             Hey!
>
>             The general idea is to have your websocket handler register
>         itself
>             using gproc[1] (or through a central gen_server) inside the
>             websocket_init/3 callback, and then have your service push
>         messages
>             to all registered handlers which you can then catch in
>         websocket_info/3.
>
>             I mention gproc because it's infinitely easier with it, as
>         you only
>             have to register all your processes under one property and
>         then send
>             a message to that property which will multicast it to all
>         registered
>             processes. And when your websocket closes, gproc takes care of
>             removing your process from the list of registered processes,
>         so you
>             really have to worry only about 2 lines of code to do
>         everything you
>             need.
>
>             Good luck!
>
>             [1] https://github.com/uwiger/____gproc
>         <https://github.com/uwiger/__gproc>
>         <https://github.com/uwiger/__gproc
>         <https://github.com/uwiger/gproc>>
>
>
>
>             On 03/16/2012 05:11 PM, AD wrote:
>
>                 Hello,
>
>                   I have cowboy setup and working to send/receive
>         websockets over a
>                 socket connection.  I am trying to figure out how to
>         initiate a
>                 message
>                 server side over that channel (without it just being a
>         reply).  I am
>                 envisioning exposing a webservice on the cowboy service that
>                 would then
>                 push a message to all connected users (or maybe a subset
>         based
>                 on some
>                 criteria).
>
>                   Does anyone know if this is possible and if so how to
>         implement?
>
>                   Cheers,
>                   -AD
>
>
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>
>
>             --
>             Loďc Hoguin
>             Erlang Cowboy
>             Nine Nines
>
>
>
>
>     --
>     Loïc Hoguin
>     Erlang Cowboy
>     Nine Nines
>
>


-- 
Loïc Hoguin
Erlang Cowboy
Nine Nines



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