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<title>s6-dns: the s6dns library interface</title>
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<p>
<a href="../">s6-dns</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> The <tt>s6dns</tt> library interface </h1>
<h2> General information </h2>
<p>
<tt>libs6dns</tt> is a DNS client library, designed for clarity
and simplicity - which translates into smallness of the code.
</p>
<p>
A major focus of <tt>libs6dns</tt> is to avoid unnecessary use
of heap memory. Memory is only allocated in the heap to store
queries and response packets during a DNS resolution process, and
to store the final answers into a user-provided
<a href="//skarnet.org/software/skalibs/libstddjb/stralloc.html">
stralloc</a>; all the other operations use stack memory, and perform
as few copies as possible.
</p>
<h2> Compiling </h2>
<ul>
<li> Make sure the s6-dns headers, as well as the skalibs headers,
are visible in your header search path. </li>
<li> Use <tt>#include <s6-dns/s6dns.h></tt> </li>
</ul>
<h2> Linking </h2>
<ul>
<li> Make sure the s6-dns libraries, as well as the skalibs libraries,
are visible in your library search path. </li>
<li> Link against <tt>-ls6dns</tt>, <tt>-lskarnet</tt>,
<tt>`cat $SYSDEPS/socket.lib`</tt> and
<tt>`cat $SYSDEPS/sysclock.lib`</tt>, $SYSDEPS being your skalibs
sysdeps directory. </li>
</ul>
<h2> Programming </h2>
<p>
The <tt>s6-dns/s6dns.h</tt> header is actually a concatenation of other headers:
the libs6dns is separated into several modules, each of them with its
own header.
</p>
<ul>
<li> The <tt>s6-dns/s6dns-constants.h</tt> header provides constants used in
other parts of the library. </li>
<li> The <a href="s6dns-ip46.html">s6-dns/s6dns-ip46.h</a> header provides an
abstraction for IPv4 and IPv6 transports. </li>
<li> The <a href="s6dns-domain.html">s6-dns/s6dns-domain.h</a> header provides
basic string manipulation primitives for domain names. </li>
<li> The <a href="s6dns-message.html">s6-dns/s6dns-message.h</a> header provides
function to parse a message following the DNS protocol. </li>
<li> The <a href="s6dns-engine.html">s6-dns/s6dns-engine.h</a> header provides
the low-level asynchronous networking functions. </li>
<li> The <a href="s6dns-rci.html">s6-dns/s6dns-rci.h</a> header provides an
interface to <tt>resolv.conf</tt> reading. </li>
<li> The <a href="s6dns-resolve.html">s6-dns/s6dns-resolve.h</a> header provides
the user-level synchronous resolution functions. </li>
<li> The <a href="hosts.html">s6-dns/hosts.h</a> header provides
functions to solve name and IP queries according the <tt>/etc/hosts</tt> file. </li>
<li> The <a href="s6dns-fmt.html">s6-dns/s6dns-fmt.h</a> header provides
formatting primitives to display RR contents. </li>
</ul>
<p>
(User-level asynchronous resolution functions are provided in the
<a href="../skadns/">skadns</a> library.)
</p>
<p>
Two functional macros are actually directly declared in the <tt>s6dns.h</tt>
header:
</p>
<ul>
<li> Call <tt>s6dns_init()</tt> before all your s6dns operations.
s6dns_init() calls <a href="s6dns-rci.html">s6dns_rci_init()</a>,
extracting <tt>resolv.conf</tt> information to an internal global
variable. The function returns 1 on success, and 0 (and sets errno)
on failure. To also use the hosts database, you can call
<tt>s6dns_init_options(1)</tt> instead. </li>
<li> Call <tt>s6dns_finish()</tt> when you're done with libs6dns.
It frees the resources used. </li>
</ul>
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