= 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
-----------

The _nng_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 _nng_rep_ protocol is the replier side, and the
<<nng_req#,nng_req(7)>> protocol is the requester side.

Socket Operations
~~~~~~~~~~~~~~~~~

The `nng_rep0_open()` call creates a requester 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_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 following protocol-specific options are available.

`NNG_OPT_MAXTTL`::

   Maximum time-to-live.  This option is an integer value
   between 0 and 255,
   inclusive, and is the maximum number of "hops" that a message may
   pass through until it is discarded.  The default value is 8.  A value
   of 0 may be used to disable the loop protection, allowing an infinite
   number of hops.

Protocol Headers
~~~~~~~~~~~~~~~~

The _nng_rep_ protocol uses a _backtrace_ in the header.  This is
more fully documented in the <<nng_req#,nng_req(7)>> manual.
    
SEE ALSO
--------
<<nng#,nng(7)>>,
<<nng_req#,nng_req(7)>>