[erlang-questions] "calling" a gen_fsm

Vance Shipley <>
Tue Sep 22 16:21:31 CEST 2015


Send your request, stuff From into StateData and return next_state. Then
you may receive the response in handle_info/3 and send it to the client
with reply/2.

On Sep 22, 2015 7:33 PM, "Garry Hodgson" <> wrote:
>
> i'm using a gen_fsm to implement the client side of
> a binary protocol. clients connect to a controller, do
> a login thing, then settle into connected state. so far,
> so good.
>
> when in connected state, i need to be able to query
> the fsm for information. some of these queries require
> sending a message to a controller and waiting for a
> response to come back. herein lies the problem, because
> the query relies on the sync event to ask the question,
> but must wait for an { ssl, Socket, Data } event to get
> the answer.
>
> i've got it sort of working, but only by intercepting the
> ssl message inline, vs. the normal handle_info() method.
> this feels like cheating, and seems fragile, as it relies on
> there being no intervening messages.
>
> so i'm wondering, is there a good/standard way of
> accomplishing this? or is gen_fsm not the right approach?
> any advice would be appreciated.
>
> thanks
>
> code snippets follow:
>
> who_provides( Service ) -> gen_fsm:sync_send_event( ?MODULE, {
request_services, Service } ).
> ...
> connected( { request_services, Service }, _From, #state{ socket=Socket,
transport=Transport } = State ) ->
>     Transport:send( Socket, service_request( Service ) ),
>     case wait_for_services( Socket ) of
>         { ok, Services } ->
>             { reply, { ok, Services }, connected, State };
>         Other ->
>             { reply, { error, Other }, connected, State }
>     end.
>
> wait_for_services( Socket ) ->
>     receive
>         { ssl, Socket, Data } ->
>             ssl:setopts( Socket, [ { active, once } ] ),
>             { ok, parse( Data ) }
>     after 30000 ->
>         timeout
>     end.
>
>
> --
> Garry Hodgson
> Lead Member of Technical Staff
> AT&T Chief Security Office (CSO)
>
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