zmq_proxy_steerable(3)
======================

NAME
----
zmq_proxy_steerable - built-in 0MQ proxy with control flow


SYNOPSIS
--------
*int zmq_proxy_steerable (const void '*frontend', const void '*backend',
     const void '*capture', const void '*control');*


DESCRIPTION
-----------

The _zmq_proxy_steerable()_ function is a variant of the _zmq_proxy()_ function.
It accepts a fourth _control_ socket.  When the _control_ socket is _NULL_ the
two functions operate identically.

When a _control_ socket of type _REP_ is provided to the proxy function the
application may send commands to the proxy.  The following commands are
supported.

_PAUSE_::
    The proxy will cease transferring messages between its endpoints.

_RESUME_::
    The proxy will resume transferring messages between its endpoints.

_TERMINATE_::
    The proxy function will exit with a return value of 0.

_STATISTICS_::
    The proxy behavior will remain unchanged and reply with a set of simple summary values of the messages that have been sent through the proxy as described next.

There are eight statistics values, each of size _uint64_t_ in the multi-part
message reply to the _STATISTICS_ command.  These are:

- number of messages received by the frontend socket

- number of bytes received by the frontend socket

- number of messages sent by the frontend socket

- number of bytes sent by the frontend socket

- number of messages received by the backend socket

- number of bytes received by the backend socket

- number of messages sent by the backend socket

- number of bytes sent by the backend socket


RETURN VALUE
------------
The _zmq_proxy_steerable()_ function returns 0 if TERMINATE is received on its
control socket.  Otherwise, it 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
-------
.Create a function to run the proxy
----
// Create the frontend and backend sockets to be proxied
void *frontend = zmq_socket (context, ZMQ_ROUTER);
void *backend = zmq_socket (context, ZMQ_DEALER);

// Create the proxy control socket
void *control = zmq_socket (context, ZMQ_REP);

// Bind the sockets.
zmq_bind (frontend, "tcp://*:5555");
zmq_bind (backend, "tcp://*:5556");
zmq_bind (control, "tcp://*:5557");

zmq_proxy_steerable(frontend, backend, NULL, control);
----
.Code in another thread/process to steer the proxy.
----
void *control = zmq_socket (context, ZMQ_REQ);
zmq_connect (control, "tcp://*:5557");

zmq_msg_t msg;

zmq_send (control, "PAUSE", 5, 0);
zmq_msg_recv (&msg, control, 0));

zmq_send (control, "RESUME", 6, 0);
zmq_msg_recv (&msg, control, 0));

zmq_send (control, "STATISTICS", 10, 0);
while (1) {
    zmq_msg_recv (&msg, control, 0));
    printf(" %lu", *(uint64_t *)zmq_msg_data (&msg));
    if (!zmq_msg_get (&msg, ZMQ_MORE))
        break;
}
printf("\n");

zmq_send (control, "TERMINATE", 9, 0);
zmq_msg_recv (&msg, control, 0));

zmq_close(frontend);
zmq_close(backend);
zmq_close(control);
----


SEE ALSO
--------
linkzmq:zmq_proxy[3]
linkzmq:zmq_bind[3]
linkzmq:zmq_connect[3]
linkzmq:zmq_socket[3]
linkzmq:zmq[7]


AUTHORS
-------
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read the 0MQ Contribution Policy at <http://www.zeromq.org/docs:contributing>.
