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<H1>[99s-extend] Websocket vs. Request-Response msg pair</H1>
<B>Graham Hay</B>
<A HREF="mailto:extend%40lists.ninenines.eu?Subject=Re%3A%20%5B99s-extend%5D%20Websocket%20vs.%20Request-Response%20msg%20pair&In-Reply-To=%3CCAABECY1-3dxX337kaShnxa3EuH1OAUyKVgonLoM9qAOQN6DNvw%40mail.gmail.com%3E"
TITLE="[99s-extend] Websocket vs. Request-Response msg pair">grahamrhay at gmail.com
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<I>Wed Jun 24 12:19:39 CEST 2015</I>
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<PRE>I think you'd have to roll your own, you just need some way to correlate
<<A HREF="http://www.enterpriseintegrationpatterns.com/CorrelationIdentifier.html">http://www.enterpriseintegrationpatterns.com/CorrelationIdentifier.html</A>>
responses
with the originating request. OTP does something similar under the hood
with gen_server calls <<A HREF="http://www.erlang.org/doc/man/gen_server.html#call-2">http://www.erlang.org/doc/man/gen_server.html#call-2</A>>
.
It's also possible to treat the ws connection as a messaging channel, and
use something like selective consumer
<<A HREF="http://www.enterpriseintegrationpatterns.com/MessageSelector.html">http://www.enterpriseintegrationpatterns.com/MessageSelector.html</A>> to
de-multiplex the messages. e.g. you could add a type/channel field to each
message, and only subscribe to those messages.
Remember that once you move into an async world, there are no guarantees
that you will receive a response! So you need to start thinking about
timeouts etc.
On 24 June 2015 at 10:18, Robert Balogh <<A HREF="https://lists.ninenines.eu/listinfo/extend">ethrbh at gmail.com</A>> wrote:
><i> hello,
</I>><i>
</I>><i> According to you grate support I got from you at yesterday, I could
</I>><i> continue my project, where I use Cowboy webserver and using Websocket. Now
</I>><i> I made an own web page with basic features I need, so the server and client
</I>><i> can communicates to eachother. I like it.
</I>><i>
</I>><i> Now I would like to step forward, and I would like to implement a
</I>><i> Request-Response mechanism. I read few articles in to this topic, and all
</I>><i> of them has mentioned this "feature" is not part of the Websocket standard.
</I>><i> They were suggested to use some sub-protocols for this, but I did not see
</I>><i> any written in Erlang.
</I>><i>
</I>><i> So, I would like to ask you, do I understand right that Cowboy does not
</I>><i> have this feature too? If so, do you have some idea how can I implement a
</I>><i> basic request-response mechanism? Probably one of you guys in this forum
</I>><i> have some idea.
</I>><i>
</I>><i> Btw, the links I read about this topic:
</I>><i>
</I>><i> <A HREF="http://stackoverflow.com/questions/10882370/websocket-request-response-subprotocol">http://stackoverflow.com/questions/10882370/websocket-request-response-subprotocol</A>
</I>><i> <A HREF="http://alabor.me/articles/request-response-oriented-websockets/">http://alabor.me/articles/request-response-oriented-websockets/</A>
</I>><i> <A HREF="https://www.npmjs.com/package/primus-responder">https://www.npmjs.com/package/primus-responder</A>
</I>><i>
</I>><i> thanks for your help,
</I>><i> /Robi
</I>><i>
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