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---
version: tip
layout: manpage_v2
title: nng_rep(7)
---
<h1>nng_rep(7)</h1>
<div class="sect1">
<h2 id="_name">NAME</h2>
<div class="sectionbody">
<div class="paragraph">
<p>nng_rep - reply protocol</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="content">
<pre class="pygments highlight"><code data-lang="c"><span></span><span class="tok-cp">#include</span><span class="tok-w"> </span><span class="tok-cpf"><nng/protocol/reqrep0/rep.h></span></code></pre>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph">
<p>
The <em>rep</em> 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.</p>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
This protocol is useful in setting up RPC-like services.
It is also reliable, in that a requester will keep retrying until
a reply is received.
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>The <em>rep</em> protocol is the replier side, and the
<a href="nng_req.7.html"><em>req</em></a> protocol is the requester side.</p>
</div>
<div class="sect2">
<h3 id="_socket_operations">Socket Operations</h3>
<div class="paragraph">
<p>The <a href="nng_rep_open.3.html"><code>nng_rep0_open()</code></a> functions create a replier socket.
This socket may be used to receive messages (requests), and then to send
replies.</p>
</div>
<div class="paragraph">
<p>Generally a reply can only be sent after receiving a request.</p>
</div>
<div class="paragraph">
<p>Send operations will result in <code>NNG_ESTATE</code> if no corresponding request
was previously received.</p>
</div>
<div class="paragraph">
<p>Likewise, only one receive operation may be pending at a time.
Any additional concurrent receive operations will result in <code>NNG_ESTATE</code>.</p>
</div>
<div class="paragraph">
<p><a href="nng.7.html#raw_mode">Raw</a> mode sockets ignore all these restrictions.</p>
</div>
</div>
<div class="sect2">
<h3 id="_context_operations">Context Operations</h3>
<div class="paragraph">
<p>This protocol supports the creation of <a href="nng_ctx.5.html">contexts</a> for concurrent
use cases using <a href="nng_ctx_open.3.html"><code>nng_ctx_open()</code></a>.</p>
</div>
<div class="paragraph">
<p>Each context may have at most one outstanding request, and operates
independently of the others.
The restrictions for order of operations with sockets apply equally
well for contexts, except that each context will be treated as if it were
a separate socket.</p>
</div>
</div>
<div class="sect2">
<h3 id="_protocol_versions">Protocol Versions</h3>
<div class="paragraph">
<p>Only version 0 of this protocol is supported.
(At the time of writing, no other versions of this protocol have been defined.)</p>
</div>
<div class="sect3">
<h4 id="_protocol_options">Protocol Options</h4>
<div class="paragraph">
<p>The <em>rep</em> protocol has no protocol-specific options.</p>
</div>
</div>
<div class="sect3">
<h4 id="_protocol_headers">Protocol Headers</h4>
<div class="paragraph">
<p>
The <em>rep</em> protocol uses a <em>backtrace</em> in the header.
This is more fully documented in the <a href="nng_req.7.html"><em>req</em></a> manual.</p>
</div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph text-left">
<p><a href="nng_rep_open.3.html">nng_rep_open(3)</a>,
<a href="nng.7.html">nng(7)</a>,
<a href="nng_req.7.html">nng_req(7)</a></p>
</div>
</div>
</div>
|
