= nng_pipe_notify(3)
//
// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
// Copyright 2018 Capitar IT Group BV <info@capitar.com>
//
// This document is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt).  A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//

== NAME

nng_pipe_notify - register pipe notification callback

== SYNOPSIS

[source, c]
----
#include <nng/nng.h>

typedef enum {
        NNG_PIPE_ADD,
        NNG_PIPE_REM,
} nng_pipe_action;

typedef void (*nng_pipe_cb)(nng_pipe, nng_pipe_action, void *);

int nng_pipe_notify(nng_socket s, nng_pipe_cb cb, void *arg);
----

== DESCRIPTION

The `nng_pipe_notify()` function registers the callback function _cb_
to be called whenever a <<nng_pipe.5#,pipe>> is added to or removed from the
socket _s_.

The function _cb_ will be called with the action `NNG_PIPE_ADD` just before
a pipe is added to the socket (as a result of a connection being established).
The final argument passed will be the argument _arg_ that was specified when
the function was registered.

The function _cb_ will also be called with the action `NNG_PIPE_REM` when
the pipe is being removed from the socket for any reason.
This will also use the same argument _arg_.

NOTE: Only one callback can be registered for a given socket. 
Subsequent calls to `nng_pipe_notify()` on the same socket will overwrite
any prior registration.

TIP: The callback _cb_ may reject a pipe for any reason by simply closing
it using `<<nng_pipe_close.3#,nng_pipe_close()>>`.
This might be done, for example, if the remote peer is not authorized to
access this session, based on values determined with the aid of
`<<nng_pipe_getopt.3#,nng_pipe_getopt()>>`.

== 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)>>,
<<nng_pipe_getopt.3#,nng_pipe_getopt(3)>>,
<<nng_pipe.5#,nng_pipe(5)>>,
<<nng_socket.5#,nng_socket(5)>>,
<<nng.7#,nng(7)>>
