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<title>s6-dns: the s6dns_ip46 library interface</title>
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<h1> The <tt>s6dns_ip46</tt> library interface </h1>
<p>
The following functions are declared in the <tt>s6-dns/s6dns-ip46.h</tt> header,
and implemented as macros.
</p>
<h2> General information </h2>
<p>
<tt>s6dns_ip46</tt> is the transport abstraction layer. It allows
the functions declared in <a href="s6dns-engine.html">s6-dns/s6dns-engine.h</a>
and <a href="s6dns-rci.html">s6-dns/s6dns-rci.h</a> to be transport-agnostic,
i.e. to be able to work with both IPv4 and IPv6.
</p>
<p>
If the underlying <a href="//skarnet.org/software/skalibs/">skalibs</a>
has been compiled with the
<a href="//skarnet.org/software/skalibs/flags.html#noipv6">--disable-ipv6</a>
configure option,
or if it has detected at build time that the target host does not support
IPv6, then the s6dns-ip46 abstraction will be totally transparent and use
no resources at all.
</p>
<h2> Data structures </h2>
<p>
A <tt>s6dns_ip46list_t</tt> structure holds a list of S6DNS_MAX_SERVERS (16)
IPv4 <em>or</em> IPv6 addresses. Such a mixed list can be constructed, for
instance, if the <tt>/etc/resolv.conf</tt> file contains both v4 and v6
<tt>nameserver</tt> lines.
</p>
<h2> Functions </h2>
<p>
If <em>list</em> is a <tt>s6dns_ip46list_t</tt> and <em>i</em> an integer
between 0 and DNS_MAX_SERVERS-1, then
</p>
<ul>
<li> <code>s6dns_ip46list_is6(&list, i)</code> is 1 if the <em>i</em>th
address in <em>list</em> is IPv6 and 0 if it is IPv4. </li>
<li> <code>s6dns_ip46list_ip(&list, i)</code> is a <tt>char *</tt> pointer to
16 (if IPv6) or 4 (IPv4) bytes representing the <em>i</em>th address in
<em>list</em>, in network byte order. </li>
</ul>
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