'\" t
.\"     Title: zmq_proxy_steerable
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 03/20/2024
.\"    Manual: 0MQ Manual
.\"    Source: 0MQ 4.3.5
.\"  Language: English
.\"
.TH "ZMQ_PROXY_STEERABLE" "3" "03/20/2024" "0MQ 4\&.3\&.5" "0MQ Manual"
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.SH "NAME"
zmq_proxy_steerable \- built\-in 0MQ proxy with control flow
.SH "SYNOPSIS"
.sp
\fBint zmq_proxy_steerable (const void \fR\fB\fI*frontend\fR\fR\fB, const void \fR\fB\fI*backend\fR\fR\fB, const void \fR\fB\fI*capture\fR\fR\fB, const void \fR\fB\fI*control\fR\fR\fB);\fR
.SH "DESCRIPTION"
.sp
The \fIzmq_proxy_steerable()\fR function is a variant of the \fIzmq_proxy()\fR function\&. It accepts a fourth \fIcontrol\fR socket\&. When the \fIcontrol\fR socket is \fINULL\fR the two functions operate identically\&.
.sp
When a \fIcontrol\fR socket of type \fIREP\fR is provided to the proxy function the application may send commands to the proxy\&. The following commands are supported\&.
.PP
\fIPAUSE\fR
.RS 4
The proxy will cease transferring messages between its endpoints\&.
.RE
.PP
\fIRESUME\fR
.RS 4
The proxy will resume transferring messages between its endpoints\&.
.RE
.PP
\fITERMINATE\fR
.RS 4
The proxy function will exit with a return value of 0\&.
.RE
.PP
\fISTATISTICS\fR
.RS 4
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\&.
.RE
.sp
There are eight statistics values, each of size \fIuint64_t\fR in the multi\-part message reply to the \fISTATISTICS\fR command\&. These are:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
number of messages received by the frontend socket
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
number of bytes received by the frontend socket
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
number of messages sent by the frontend socket
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
number of bytes sent by the frontend socket
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
number of messages received by the backend socket
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
number of bytes received by the backend socket
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
number of messages sent by the backend socket
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
number of bytes sent by the backend socket
.RE
.SH "RETURN VALUE"
.sp
The \fIzmq_proxy_steerable()\fR 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)\&.
.SH "EXAMPLE"
.PP
\fBCreate a function to run the proxy\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
// 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);
.fi
.if n \{\
.RE
.\}
.PP
\fBCode in another thread/process to steer the proxy.\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
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("\en");

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

zmq_close(frontend);
zmq_close(backend);
zmq_close(control);
.fi
.if n \{\
.RE
.\}
.sp
.SH "SEE ALSO"
.sp
\fBzmq_proxy\fR(3) \fBzmq_bind\fR(3) \fBzmq_connect\fR(3) \fBzmq_socket\fR(3) \fBzmq\fR(7)
.SH "AUTHORS"
.sp
This page was written by the 0MQ community\&. To make a change please read the 0MQ Contribution Policy at \m[blue]\fBhttp://www\&.zeromq\&.org/docs:contributing\fR\m[]\&.