zmq_proxy(3)

1ZMQ_PROXY(3)                      0MQ Manual                      ZMQ_PROXY(3)
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NAME

6       zmq_proxy - start built-in 0MQ proxy
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SYNOPSIS

9       int zmq_proxy (void *frontend, void *backend, void *capture);
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DESCRIPTION

12       The zmq_proxy() function starts the built-in 0MQ proxy in the current
13       application thread.
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15       The proxy connects a frontend socket to a backend socket. Conceptually,
16       data flows from frontend to backend. Depending on the socket types,
17       replies may flow in the opposite direction. The direction is conceptual
18       only; the proxy is fully symmetric and there is no technical difference
19       between frontend and backend.
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21       Before calling zmq_proxy() you must set any socket options, and connect
22       or bind both frontend and backend sockets. The two conventional proxy
23       models are:
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25       zmq_proxy() runs in the current thread and returns only if/when the
26       current context is closed.
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28       If the capture socket is not NULL, the proxy shall send all messages,
29       received on both frontend and backend, to the capture socket. The
30       capture socket should be a ZMQ_PUB, ZMQ_DEALER, ZMQ_PUSH, or ZMQ_PAIR
31       socket.
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33       Refer to zmq_socket(3) for a description of the available socket types.
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EXAMPLE USAGE

36   Shared Queue
37       When the frontend is a ZMQ_ROUTER socket, and the backend is a
38       ZMQ_DEALER socket, the proxy shall act as a shared queue that collects
39       requests from a set of clients, and distributes these fairly among a
40       set of services. Requests shall be fair-queued from frontend
41       connections and distributed evenly across backend connections. Replies
42       shall automatically return to the client that made the original
43       request.
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45   Forwarder
46       When the frontend is a ZMQ_XSUB socket, and the backend is a ZMQ_XPUB
47       socket, the proxy shall act as a message forwarder that collects
48       messages from a set of publishers and forwards these to a set of
49       subscribers. This may be used to bridge networks transports, e.g. read
50       on tcp:// and forward on pgm://.
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52   Streamer
53       When the frontend is a ZMQ_PULL socket, and the backend is a ZMQ_PUSH
54       socket, the proxy shall collect tasks from a set of clients and
55       forwards these to a set of workers using the pipeline pattern.
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RETURN VALUE

58       The zmq_proxy() function always returns -1 and errno set to ETERM or
59       EINTR (the 0MQ context associated with either of the specified sockets
60       was terminated) or EFAULT (the provided frontend or backend was
61       invalid).
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EXAMPLE

64       Creating a shared queue proxy.
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66           //  Create frontend and backend sockets
67           void *frontend = zmq_socket (context, ZMQ_ROUTER);
68           assert (frontend);
69           void *backend = zmq_socket (context, ZMQ_DEALER);
70           assert (backend);
71           //  Bind both sockets to TCP ports
72           assert (zmq_bind (frontend, "tcp://*:5555") == 0);
73           assert (zmq_bind (backend, "tcp://*:5556") == 0);
74           //  Start the queue proxy, which runs until ETERM
75           zmq_proxy (frontend, backend, NULL);
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AUTHORS

82       This page was written by the 0MQ community. To make a change please
83       read the 0MQ Contribution Policy at
84       http://www.zeromq.org/docs:contributing.
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880MQ 4.3.4                         01/21/2023                      ZMQ_PROXY(3)