= nng_dial(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_dial - create and start dialer

== SYNOPSIS

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

int nng_dial(nng_socket s, const char *url, nng_dialer *dp, int flags);
----

== DESCRIPTION

The `nng_dial()` function creates a newly initialized
xref:nng_dialer.5.adoc[`nng_dialer`] object,
associated with socket _s_, and configured to dial the
address specified by _url_, and starts it.
If the value of _dp_ is not `NULL`, then
the newly created dialer is stored at the address indicated by _dp_.

Dialers initiate a remote connection to a listener.
Upon a successful
connection being established, they create a xref:nng_pipe.5.adoc[pipe],
add it to the socket, and then wait for that pipe to be closed.
When the pipe is closed, the dialer attempts to re-establish the connection.
Dialers will also periodically retry a connection automatically if an attempt
to connect asynchronously fails.

TIP: While it is convenient to think of dialers as "`clients`", the relationship
between the listener or dialer is orthogonal to any server or client status
that might be associated with a given protocol.
For example, a xref:nng_req.7.adoc[_req_]
socket might have associated dialers, but might also have associated listeners.
It may even have some of each at the same time!

Normally, the first attempt to connect to the address indicated by _url_ is done
synchronously, including any necessary name resolution.
As a result, a failure, such as if the connection is refused, will be returned
immediately, and no further action will be taken.

However, if the special value `NNG_FLAG_NONBLOCK` is
supplied in _flags_, then the connection attempt is made asynchronously.

Furthermore, if the connection was closed for a synchronously dialed
connection, the dialer will still attempt to redial asynchronously.

TIP: While `NNG_FLAG_NONBLOCK` can help an application be more resilient,
it also generally makes diagnosing failures somewhat more difficult.

Because the dialer is started immediately, it is generally not possible
to apply extra configuration; if that is needed applications should consider
using xref:nng_dialer_create.3.adoc[`nng_dialer_create()`] and
xref:nng_dialer_start.3.adoc[`nng_dialer_start()`] instead.

== RETURN VALUES

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

== ERRORS

[horizontal]
`NNG_EADDRINVAL`:: An invalid _url_ was specified.
`NNG_ECLOSED`:: The socket _s_ is not open.
`NNG_ECONNREFUSED`:: The remote peer refused the connection.
`NNG_ECONNRESET`:: The remote peer reset the connection.
`NNG_EINVAL`:: An invalid set of _flags_ or an invalid _url_ was specified.
`NNG_ENOMEM`:: Insufficient memory is available.
`NNG_EPEERAUTH`:: Authentication or authorization failure.
`NNG_EPROTO`:: A protocol error occurred.
`NNG_EUNREACHABLE`:: The remote address is not reachable.

== SEE ALSO

[.text-left]
xref:nng_dialer_close.3.adoc[nng_dialer_close(3)],
xref:nng_dialer_create.3.adoc[nng_dialer_create(3)]
xref:nng_dialer_start.3.adoc[nng_dialer_start(3)],
xref:nng_listen.3.adoc[nng_listen(3)],
xref:nng_strerror.3.adoc[nng_strerror(3)],
xref:nng_dialer.5.adoc[nng_dialer(5)],
xref:nng_pipe.5.adoc[nng_pipe(5)],
xref:nng.7.adoc[nng(7)]