NAME

       zmq_proxy - start built-in 0MQ proxy

SYNOPSIS

       int zmq_proxy (void *frontend, void *backend, 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 or EINTR (the 0MQ
       context associated with either of the specified sockets was terminated) or EFAULT (the
       provided frontend or backend was invalid).

EXAMPLE

       Creating a shared queue proxy.

           //  Create frontend and backend sockets
           void *frontend = zmq_socket (context, ZMQ_ROUTER);
           assert (frontend);
           void *backend = zmq_socket (context, ZMQ_DEALER);
           assert (backend);
           //  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

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       Contribution Policy at http://www.zeromq.org/docs:contributing.