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ZMQ_PROXY(3)                      0MQ Manual                      ZMQ_PROXY(3)


NAME

       zmq_proxy - start built-in 0MQ proxy


SYNOPSIS

       int zmq_proxy (const void *frontend, const void *backend, const void
       *capture);


DESCRIPTION

       The zmq_proxy() function starts the built-in 0MQ proxy in the current
       application thread.

       The proxy connects a frontend socket to a backend socket. Conceptually,
       data flows from frontend to backend. Depending on the socket types,
       replies may flow in the opposite direction. The direction is conceptual
       only; the proxy is fully symmetric and there is no technical difference
       between frontend and backend.

       Before calling zmq_proxy() you must set any socket options, and connect
       or bind both frontend and backend sockets. The two conventional proxy
       models are:

       zmq_proxy() runs in the current thread and returns only if/when the
       current context is closed.

       If the capture socket is not NULL, the proxy shall send all messages,
       received on both frontend and backend, to the capture socket. The
       capture socket should be a ZMQ_PUB, ZMQ_DEALER, ZMQ_PUSH, or ZMQ_PAIR
       socket.

       Refer to zmq_socket(3) for a description of the available socket types.


EXAMPLE USAGE

   Shared Queue
       When the frontend is a ZMQ_ROUTER socket, and the backend is a
       ZMQ_DEALER socket, the proxy shall act as a shared queue that collects
       requests from a set of clients, and distributes these fairly among a
       set of services. Requests shall be fair-queued from frontend
       connections and distributed evenly across backend connections. Replies
       shall automatically return to the client that made the original
       request.

   Forwarder
       When the frontend is a ZMQ_XSUB socket, and the backend is a ZMQ_XPUB
       socket, the proxy shall act as a message forwarder that collects
       messages from a set of publishers and forwards these to a set of
       subscribers. This may be used to bridge networks transports, e.g. read
       on tcp:// and forward on pgm://.

   Streamer
       When the frontend is a ZMQ_PULL socket, and the backend is a ZMQ_PUSH
       socket, the proxy shall collect tasks from a set of clients and
       forwards these to a set of workers using the pipeline pattern.


RETURN VALUE

       The zmq_proxy() function always returns -1 and errno set to ETERM (the
       0MQ context associated with either of the specified sockets was
       terminated).


EXAMPLE

       Creating a shared queue proxy.

           //  Create frontend and backend sockets
           void *frontend = zmq_socket (context, ZMQ_ROUTER);
           assert (backend);
           void *backend = zmq_socket (context, ZMQ_DEALER);
           assert (frontend);
           //  Bind both sockets to TCP ports
           assert (zmq_bind (frontend, "tcp://*:5555") == 0);
           assert (zmq_bind (backend, "tcp://*:5556") == 0);
           //  Start the queue proxy, which runs until ETERM
           zmq_proxy (frontend, backend, NULL);


SEE ALSO

       zmq_bind(3) zmq_connect(3) zmq_socket(3) zmq(7)


AUTHORS

       This page was written by the 0MQ community. To make a change please
       read the 0MQ Contribution Policy at
       http://www.zeromq.org/docs:contributing.

0MQ 4.1.0                         08/17/2015                      ZMQ_PROXY(3)

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