= nng_rep(7)
//
// 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_rep - reply protocol

== SYNOPSIS

[source,c]
----
#include <nng/protocol/reqrep0/rep.h>

int nng_rep0_open(nng_socket *s);
----

== DESCRIPTION

(((protocol, _rep_)))
The ((_rep_ protocol)) is one half of a ((request/reply pattern)).
In this pattern, a requester sends a message to one replier, who
is expected to reply.
The request is resent if no reply arrives,
until a reply is received or the request times out.

TIP: This protocol is useful in setting up RPC-like services.
It is also "`reliable`", in that a the requester will keep retrying until
a reply is received.

The _rep_ protocol is the replier side, and the
<<nng_req.7#,_req_>> protocol is the requester side.

=== Socket Operations

The <<nng_rep_open.3#,`nng_rep0_open()`>> call creates a replier socket.
This socket may be used to receive messages (requests), and then to send
replies.
Generally a reply can only be sent after receiving a request.
(Attempts to receive a message will result in `NNG_ESTATE` if there
is no outstanding request.)

Attempts to send on a socket with no outstanding requests will result
in `NNG_ESTATE`. 

Raw mode sockets (set with <<nng_options.5#NNG_OPT_RAW,`NNG_OPT_RAW`>>)
ignore all these restrictions.

=== Protocol Versions

Only version 0 of this protocol is supported.
(At the time of writing, no other versions of this protocol have been defined.)

==== Protocol Options

The _rep_ protocol has no protocol-specific options.

==== Protocol Headers

(((backtrace)))
The _rep_ protocol uses a _backtrace_ in the header.
This is more fully documented in the <<nng_req.7#,_req_>> manual.
    
== SEE ALSO

<<nng_rep_open.3#,nng_rep_open(3)>>,
<<nng.7#,nng(7)>>,
<<nng_req.7#,nng_req(7)>>