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'\" t
.\" Title: zmq_proxy
.\" Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets v1.76.1 <http://docbook.sf.net/>
.\" Date: 10/14/2014
.\" Manual: 0MQ Manual
.\" Source: 0MQ 4.0.5
.\" Language: English
.\"
.TH "ZMQ_PROXY" "3" "10/14/2014" "0MQ 4\&.0\&.5" "0MQ Manual"
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.nh
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
zmq_proxy \- start built\-in 0MQ proxy
.SH "SYNOPSIS"
.sp
\fBint zmq_proxy (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);\fR
.SH "DESCRIPTION"
.sp
The \fIzmq_proxy()\fR function starts the built\-in 0MQ proxy in the current application thread\&.
.sp
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\&.
.sp
Before calling \fIzmq_proxy()\fR you must set any socket options, and connect or bind both frontend and backend sockets\&. The two conventional proxy models are:
.sp
\fIzmq_proxy()\fR runs in the current thread and returns only if/when the current context is closed\&.
.sp
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 \fIZMQ_PUB\fR, \fIZMQ_DEALER\fR, \fIZMQ_PUSH\fR, or \fIZMQ_PAIR\fR socket\&.
.sp
Refer to \fBzmq_socket\fR(3) for a description of the available socket types\&.
.SH "EXAMPLE USAGE"
.SS "Shared Queue"
.sp
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\&.
.SS "Forwarder"
.sp
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://\&.
.SS "Streamer"
.sp
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\&.
.SH "RETURN VALUE"
.sp
The \fIzmq_proxy()\fR function always returns \-1 and \fIerrno\fR set to \fBETERM\fR (the 0MQ \fIcontext\fR associated with either of the specified sockets was terminated)\&.
.SH "EXAMPLE"
.PP
\fBCreating a shared queue proxy\fR.
.sp
.if n \{\
.RS 4
.\}
.nf
// 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);
.fi
.if n \{\
.RE
.\}
.sp
.SH "SEE ALSO"
.sp
\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[]\&.
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