cant send data back to sending socket

[lpgauth]

cant send data back to sending socket

[ergl]

Hi! If I'm understanding you correctly, you don't know how to send the reply back to the original sender of the data inside the handle_data/2, right?

That function expects you reply with {ok, [response()], State}, where response() is {external_request_id(), term()}. This means that you have to return whatever request identifier you used to originally send your message to the server.

Check out an example with the arithmetic_tcp_client module under the test folder:

shackle/test/arithmetic_tcp_client.erl

Lines 103 to 112 in f92c2e1

	handle_request({Operation, A, B}, #state {
	request_counter = RequestCounter
	} = State) ->
	RequestId = arithmetic_protocol:request_id(RequestCounter),
	Data = arithmetic_protocol:request(RequestId, Operation, A, B),
	{ok, RequestId, Data, State#state {
	request_counter = RequestCounter + 1
	}}.

The client creates a new request id, and generates a new message with it:

shackle/test/arithmetic_protocol.erl

Lines 34 to 37 in f92c2e1

	-spec request(int(), operation(), tiny_int(), tiny_int()) -> binary().
	request(ReqId, Operation, A, B) ->
	<<ReqId:32/integer, (opcode(Operation)), A:8/integer, B:8/integer>>.

As you can see, the original request id is part of the binary we send to the server, which should reply back with the id so that the client can re-use it:

shackle/test/arithmetic_tcp_client.erl

Lines 89 to 98 in f92c2e1

	handle_data(Data, #state {
	buffer = Buffer
	} = State) ->
	Data2 = <<Buffer/binary, Data/binary>>,
	{Replies, Buffer2} = arithmetic_protocol:parse_replies(Data2),
	{ok, Replies, State#state {
	buffer = Buffer2
	}}.

Inside parse_replies, we extract the request identifier from the server message:

shackle/test/arithmetic_protocol.erl

Lines 45 to 48 in f92c2e1

	parse_replies(<<ReqId:32/integer, A:16/integer, Rest/binary>>, Acc) ->
	parse_replies(Rest, [{ReqId, A} | Acc]);
	parse_replies(Buffer, Acc) ->
	{Acc, Buffer}.

As such, when arithmetic_tcp_client:handle_data/2 returns, the pool is able to match the original request id to the original sender, and return it.

Hope this helps!

[nayibor]

hi.
thanks very much for the help and sorry for late reply.
thanks for the samples and its shed a lot of light on how the library works.
from our end whats happening is that the processes themselves are the direct connection between themselves and the tcp server.
there is no client sending a message with shackle acting as sort of a proxy.
i think thats the major difference.
so the thing is that when the shackle process gets the data,it just processes it and sends it back if necessary.
so i was confused because there is no way to know how to send data directly to the requesting party.
thanks!!

[lpgauth]

You can still use shackle without a request_id() if your response are in order. All you have to do it keep a counter of requests out and requests in.

[nayibor]

please can u give me an example of that.
there is an example you cited above containing the counter but that also contains the request id.

[lpgauth]

You need to keep two counters (one for requests out and one for requests in).

See https://github.com/lpgauth/buoy/blob/master/src/buoy_client.erl