ZMQ_PROXY - Online Linux Manual Page

Section : 3
Updated : 01/21/2023
Source : 0MQ 4.3.4
Note : 0MQ Manual

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

EINTR

(the 0MQ

context

associated with either of the specified sockets was terminated) or

EFAULT

(the provided

frontend

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);