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---
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---
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<title>nn_recvmsg(3compat)</title>
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<h1>nn_recvmsg(3compat) Manual Page</h1>
<div id="toc" class="toc2">
<div id="toctitle">Table of Contents</div>
<ul class="sectlevel1">
<li><a href="#_synopsis">SYNOPSIS</a></li>
<li><a href="#_description">DESCRIPTION</a></li>
<li><a href="#_return_values">RETURN VALUES</a></li>
<li><a href="#_errors">ERRORS</a></li>
<li><a href="#_see_also">SEE ALSO</a></li>
</ul>
</div>
<h2 id="_name">NAME</h2>
<div class="sectionbody">
<p>nn_recvmsg - receive message (compatible API)</p>
</div>
</div>
<div id="content">
<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-cpf"><nanomsg/nn.h></span><span class="tok-cp"></span>
<span class="tok-kt">int</span> <span class="tok-nf">nn_recvmsg</span><span class="tok-p">(</span><span class="tok-kt">int</span> <span class="tok-n">sock</span><span class="tok-p">,</span> <span class="tok-k">struct</span> <span class="tok-n">nn_msghdr</span> <span class="tok-o">*</span><span class="tok-n">hdr</span><span class="tok-p">,</span> <span class="tok-kt">int</span> <span class="tok-n">flags</span><span class="tok-p">);</span></code></pre>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The <code>nn_recvmsg()</code> function receives a message into the header described by
<em>hdr</em> using the socket <em>sock</em>.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
This function is provided for API
<a href="nng_compat.3compat.html">compatibility</a> with legacy <em>libnanomsg</em>.
Consider using the relevant <a href="libnng.3.html">modern API</a> instead.
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>The <em>flags</em> field may contain the special flag <code>NN_DONTWAIT</code>.
In this case, if no message is ready for receiving on <em>sock</em>,
the operation shall not block, but instead will fail with the error <code>EAGAIN</code>.</p>
</div>
<div class="paragraph">
<p>The <em>hdr</em> points to a structure of type <code>struct nn_msghdr</code>, which has the
following definition:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="pygments highlight"><code data-lang="c"><span></span><span class="tok-k">struct</span> <span class="tok-n">nn_iovec</span> <span class="tok-p">{</span>
<span class="tok-kt">void</span> <span class="tok-o">*</span> <span class="tok-n">iov_base</span><span class="tok-p">;</span>
<span class="tok-kt">size_t</span> <span class="tok-n">iov_len</span><span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-k">struct</span> <span class="tok-n">nn_msghdr</span> <span class="tok-p">{</span>
<span class="tok-k">struct</span> <span class="tok-n">nn_iovec</span> <span class="tok-o">*</span><span class="tok-n">msg_iov</span><span class="tok-p">;</span>
<span class="tok-kt">int</span> <span class="tok-n">msg_iovlen</span><span class="tok-p">;</span>
<span class="tok-kt">void</span> <span class="tok-o">*</span> <span class="tok-n">msg_control</span><span class="tok-p">;</span>
<span class="tok-kt">size_t</span> <span class="tok-n">msg_controllen</span><span class="tok-p">;</span>
<span class="tok-p">};</span></code></pre>
</div>
</div>
<div class="paragraph">
<p>The <code>msg_iov</code> is an array of scatter items, permitting the message
to be spread into different memory blocks.
There are <code>msg_iovlen</code> elements in this array, each of which
has the base address (<code>iov_base</code>) and length (<code>iov_len</code>) indicated.</p>
</div>
<div class="paragraph">
<p>The last member of this array may have the <code>iov_len</code> field set to <code>NN_MSG</code>,
in which case the function shall allocate a message buffer, and store the
pointer to it at the address indicated by <code>iov_base</code>.
This can help save an extra copy operation.
The buffer should be deallocated by <a href="nn_freemsg.3compat.html"><code>nn_freemsg()</code></a>
or similar when it is no longer needed.</p>
</div>
<div class="paragraph">
<p>The values of <code>msg_control</code> and <code>msg_controllen</code> describe a buffer
of ancillary data associated with the message.
This is currently only useful to obtain the message headers
used with <a href="nng.7.html#raw_mode">raw mode</a> sockets.
In all other circumstances these fields should be zero.
Details about this structure are covered in
<a href="nn_cmsg.3compat.html"><code>nn_cmsg(3compat)</code></a>.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_return_values">RETURN VALUES</h2>
<div class="sectionbody">
<div class="paragraph">
<p>This function returns the number of bytes received on success, and -1 on error.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_errors">ERRORS</h2>
<div class="sectionbody">
<div class="hdlist">
<table>
<tr>
<td class="hdlist1">
<code>EAGAIN</code>
</td>
<td class="hdlist2">
<p>The operation would block.</p>
</td>
</tr>
<tr>
<td class="hdlist1">
<code>EBADF</code>
</td>
<td class="hdlist2">
<p>The socket <em>sock</em> is not open.</p>
</td>
</tr>
<tr>
<td class="hdlist1">
<code>EFSM</code>
</td>
<td class="hdlist2">
<p>The socket cannot receive in this state.</p>
</td>
</tr>
<tr>
<td class="hdlist1">
<code>EINVAL</code>
</td>
<td class="hdlist2">
<p>The <em>hdr</em> is invalid.</p>
</td>
</tr>
<tr>
<td class="hdlist1">
<code>ENOTSUP</code>
</td>
<td class="hdlist2">
<p>This protocol cannot receive.</p>
</td>
</tr>
<tr>
<td class="hdlist1">
<code>ETIMEDOUT</code>
</td>
<td class="hdlist2">
<p>Operation timed out.</p>
</td>
</tr>
</table>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph text-left">
<p><a href="nn_cmsg.3compat.html">nn_cmsg(3compat)</a>,
<a href="nn_errno.3compat.html">nn_errno(3compat)</a>,
<a href="nn_recv.3compat.html">nn_recv(3compat)</a>,
<a href="nn_send.3compat.html">nn_send(3compat)</a>,
<a href="nn_socket.3compat.html">nn_socket(3compat)</a>,
<a href="nng_compat.3compat.html">nn_compat(3compat)</a>,
<a href="nng.7.html">nng(7)</a></p>
</div>
</div>
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