---
name: "zmq_proxy_steerable"
section: "3"
platform: "linux"
package: "zeromq"
version: "4.3.5-3"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/zmq_proxy_steerable"
---

# zmq\_proxy\_steerable(3)

built-in 0MQ proxy with control flow

## 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

[**zmq\_proxy**(3)](/zmq_proxy/3.md) [**zmq\_bind**(3)](/zmq_bind/3.md) [**zmq\_connect**(3)](/zmq_connect/3.md) [**zmq\_socket**(3)](/zmq_socket/3.md) [**zmq**(7)](/zmq/7.md)

## AUTHORS

This page was written by the 0MQ community. To make a change please read the 0MQ Contribution Policy at **http://www.zeromq.org/docs:contributing**.