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<title>s6-dns: the s6dns_rci library interface</title>
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<p>
<a href="index.html">libs6dns</a><br />
<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_rci</tt> library interface </h1>
<p>
The following functions and structures are declared in the <tt>s6-dns/s6dns-rci.h</tt> header,
and implemented in the <tt>libs6dns.a</tt> or <tt>libs6dns.so</tt> library.
</p>
<h2> General information </h2>
<p>
<tt>s6dns_rci</tt> provides functions to get information from
the <tt>/etc/resolv.conf</tt> file.
</p>
<h2> Data structures </h2>
<p>
A <tt>s6dns_rci_t</tt> is a structure storing information
provided by the <tt>/etc/resolv.conf</tt> file, i.e.
</p>
<ul>
<li> The list of "nameserver" addresses, i.e. IP addresses of DNS caches
contacted by clients for recursive queries </li>
<li> The list of qualification rules provided by "domain" or "search"
lines </li>
</ul>
<p>
Nameserver addresses are stored in a
<a href="s6dns-ip46.html">s6dns_ip46list_t</a>. Qualification rules are
stored in a <a href="//skarnet.org/software/skalibs/libstddjb/stralloc.html">stralloc</a>
with an additional integer storing the number of rules.
</p>
<p>
Most programs won't need more than one <tt>s6dns_rci_t</tt>, so
the library provides the global variable <tt>s6dns_rci_here</tt>, used
by default in simple resolution macros.
</p>
<h2> Functions </h2>
<p>
<code> int s6dns_rci_init (s6dns_rci_t *rci, char const *file) </code> <br />
Extracts information from <em>file</em>, which must be in <tt>/etc/resolv.conf</tt>
format, and stores it into *<em>rci</em>. <em>rci</em> must be previously
initialized to the <tt>S6DNS_RCI_ZERO</tt> constant. The function returns 1 if
it succeeds, or 0 (and sets errno) if it fails.
</p>
<p>
If the DNSCACHEIP environment variable is set, and contains a list of
IP addresses separated by commas, semicolons, spaces, tabs, newlines or
carriage returns, then this list overrides any nameserver information
from <em>file</em>. If the variable is empty, <em>file</em> will be used
as the source of the information.
</p>
<p>
If the DNSQUALIFY environment variable is set, a list of domain suffixes,
separated by spaces, tabs, newlines or carriage returns, is read from it,
and overrides any qualification information from <em>file</em>. If the
variable is empty, it amounts to one rule saying "no qualification".
</p>
<p>
<tt>s6dns_init()</tt> is an alias to
<tt>s6dns_rci_init(&s6dns_rci_here, "/etc/resolv.conf")</tt>.
</p>
<p>
<code> void s6dns_rci_free (s6dns_rci_t *rci) </code> <br />
Frees the memory used by *<em>rci</em>. <em>rci</em> is then suitable to
be reused in a <tt>s6dns_rci_init</tt> call.
</p>
<p>
<tt>s6dns_finish()</tt> calls <tt>s6dns_rci_free(&s6dns_rci_here)</tt>.
</p>
<p>
<code> unsigned int s6dns_qualify (s6dns_domain_t *list, s6dns_domain_t const *d) </code> <br />
Qualifies domain *<em>d</em> into the list of domains pointed to by <em>list</em>
according to the rules stored in <tt>s6dns_rci_here</tt>. Returns the number of
written domains (0 if it fails); this number cannot exceed
<tt>s6dns_rci_here.rulesnum</tt>.
</p>
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