---
name: "nng_pipe_notify"
section: "3"
platform: "linux"
package: "libnng-dev"
version: "1.10.1-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nng_pipe_notify"
---

# nng\_pipe\_notify(3)

register pipe notification callback

## NAME

nng\_pipe\_notify - register pipe notification callback

## SYNOPSIS

```
#include <nng/nng.h>
typedef enum {
        NNG_PIPE_EV_ADD_PRE,
        NNG_PIPE_EV_ADD_POST,
        NNG_PIPE_EV_REM_POST,
} nng_pipe_ev;
typedef void (*nng_pipe_cb)(nng_pipe, nng_pipe_ev, void *);
int nng_pipe_notify(nng_socket s, nng_pipe_ev ev, nng_pipe_cb cb, void *arg);
```

## DESCRIPTION

The `nng_pipe_notify()` function registers the callback function *cb* to be called whenever a pipe the pipe event specified by *ev* occurs on the socket *s*. The callback *cb* will be passed *arg* as its final argument.

A different callback may be supplied for each event. Each event may have at most one callback registered. Registering a callback implicitly unregisters any previously registered.

The following pipe events are supported:

`NNG_PIPE_EV_ADD_PRE`

This event occurs after a connection and negotiation has completed, but before the pipe is added to the socket. If the pipe is closed (using `nng_pipe_close()`) at this point, the socket will never see the pipe, and no further events will occur for the given pipe.

`NNG_PIPE_EV_ADD_POST`

This event occurs after the pipe is fully added to the socket. Prior to this time, it is not possible to communicate over the pipe with the socket.

`NNG_PIPE_EV_REM_POST`

This event occurs after the pipe has been removed from the socket. The underlying transport may be closed at this point, and it is not possible communicate using this pipe.

**Warning**\

The callback *cb* function must **not** attempt to perform any accesses to the socket, as it is called with a lock on the socket held! Doing so would thus result in a deadlock.

**Tip**\

The callback *cb* may close a pipe for any reason by simply closing it using `nng_pipe_close()`. This might be done before the pipe is added to the socket (during `NNG_PIPE_EV_ADD_PRE`), for example, if the remote peer is not authorized.

**Tip**\

It is possible to register the same *cb* and *arg* for different events by calling this function separately for different values of *ev*.

**Note**\

This function ignores invalid values for *ev*.

## RETURN VALUES

This function returns 0 on success, and non-zero otherwise.

## ERRORS

`NNG_ECLOSED`

The socket *s* does not refer to an open socket.

## SEE ALSO

[nng\_pipe\_close(3)](/nng_pipe_close/3.md), [nng\_pipe\_getopt(3)](/nng_pipe_getopt/3.md), [nng\_pipe(5)](/nng_pipe/5.md), [nng\_socket(5)](/nng_socket/5.md), [nng(7)](/nng/7.md)