[zeromq-dev] Empty message does not close ZMQ_STREAM socket?

Greg Young gregoryyoung1 at gmail.com
Mon Mar 21 15:48:07 CET 2016


I couldn't find a lot of docs on this stuff so I experimented a bit to
try learning about ZMQ_STREAM. Here are two echo servers (one a simple
program the other as an actor
https://github.com/gregoryyoung/zmq-stream-echo/blob/master/src/echoactorserver.c)

I was curious about this question so added this functionality (exit closes now).

The main difference I see in my code is you still set:

    server.send(empty, ZMQ_SNDMORE );

ZMQ_SENDMORE which I don't think you really want to be sending more?

Cheers,

Greg

On Mon, Mar 21, 2016 at 9:06 AM, Auer, Jens <jens.auer at cgi.com> wrote:
> Hi,
>
> I am trying to close a TCP socket over a ZMQ_STREAM by sending an identity
> frame followed by an empty message, as described in the manual ("To close a
> specific connection, send the identity frame followed by a zero-length
> message"). I have a simple client/server example:
> #include <zmq.hpp>
> #include <iostream>
> #include <cstdlib>
>
> int main2() {
>     std::string address = "tcp://127.0.0.1:5000";
>
>     zmq::context_t zmq;
>     zmq::socket_t server(zmq, ZMQ_STREAM);
>
>     server.bind(address);
>
>     zmq::message_t id;
>     zmq::message_t m;
>     server.recv(&id);
>     server.recv(&m);
>     std::cout << "Connection received: " << id.size() << std::endl;
>
>     zmq::message_t empty{};
>
>     server.send(id, ZMQ_SNDMORE);
>     server.send(empty, ZMQ_SNDMORE );
>
>     int i;
>     std::cin >> i;
>
>     return 0;
> }
>
> #include <zmq.hpp>
> #include <iostream>
>
> int main() {
>     std::string address = "tcp://127.0.0.1:5000";
>
>     zmq::context_t zmq;
>     zmq::socket_t client(zmq, ZMQ_STREAM);
>
>     client.connect(address);
>
>     zmq::message_t m3;
>     zmq::message_t m4;
>     client.recv(&m3);
>     client.recv(&m4);
>
>     std::cout << "Connection established" << std::endl;
>
>     {
>         zmq::message_t m5;
>         zmq::message_t m6;
>         client.recv(&m5);
>         client.recv(&m6);
>     }
>
>     std::cout << "Connection closed" << std::endl;
>     int i;
>     std::cin >> i;
>
>     return 0;
> }
>
> When I start the server and then the client, the server will receive the
> connection message, but the empty message does not close the socket:
> ./stream_s 2
> Connection received: 5
> /tmp/stream_c
> Connection established
>
> tcp        0      0 127.0.0.1:5000          0.0.0.0:*               LISTEN
> 32615/./stream_s
> tcp        0      0 127.0.0.1:5000          127.0.0.1:34270
> ESTABLISHED 32615/./stream_s
> tcp        0      0 127.0.0.1:34270         127.0.0.1:5000
> ESTABLISHED 32618/stream_c
>
> I have also created a second example where the server sends the close
> message twice. Here, the client actually receives the close message as an
> empty message. Why is this even possible over a ZMQ_STREAM socket?
>
> I am using ZeroMQ 4.1.4, so the notification messages should be enabled by
> default without setting ZMQ_STREAM_NOTIFY, and I have also tested 4.1.2 to
> check for a regression.
>
> Best wishes,
>   Jens
>
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> zeromq-dev mailing list
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>



-- 
Studying for the Turing test



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