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<title>s6-dns: the s6dns_hosts library interface</title>
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<p>
<a href="index.html">libs6dns</a><br />
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<a href="//skarnet.org/software/">Software</a><br />
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<h1> The <tt>s6dns_hosts</tt> library interface </h1>
<p>
The following functions are declared in the <tt>s6-dns/hosts.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_hosts</tt> provides functions and macros - mostly macros -
to perform name-to-IP or IP-to-name resolution according to the
local <tt>/etc/hosts</tt> file.
</p>
<p>
Most of the functions declared here are variations of another, more
generic function. Typically, a <em>foobar_r</em> function is the
generic one, and will take additional arguments such as: a pointer to
a local hosts database (compiled to an efficient format), and/or a
list and number of rules for qualification. The corresponding <em>foobar</em>
function is the same, except that it uses global variables to fill
these additional arguments: for instance, the hosts database made from
<tt>/etc/hosts</tt>, or the qualification rules computed from
<tt>/etc/resolv.conf</tt>. We document the simpler functions — even
though they're macros, we pretend they're functions; please refer to
the <a href="https://git.skarnet.org/cgi-bin/cgit.cgi/s6-dns/tree/src/include/s6-dns/hosts.h">s6-dns/hosts.h</a>
file for the exact prototypes or if you want to use the generic functions.
</p>
<ul>
<li> <tt>s6dns_engine_here</tt>: a global
<a href="s6dns-engine.html">s6dns_engine_t</a> storing the current
query, for sequential queries. </li>
<li> <tt>s6dns_debughook_zero</tt>: a global <tt>s6dns_debughook_t</tt>
meaning no debugging is needed. </li>
<li> <tt>s6dns_rci_here</tt>: a global
<a href="s6dns-rci.html">s6dns_rci_t</a> containing the current
resolv.conf information. </li>
</ul>
<h2> Global variables </h2>
<p>
<code> cdb s6dns_hosts_here </code> <br />
<tt>s6dns_hosts_here</tt> is the global <tt>cdb</tt> database containing
the compiled data from <tt>/etc/hosts</tt>. You normally do not need to
use it manually because it is implicitly supplied to functions when you
use the macros without a <tt>_r</tt> suffix.
</p>
<h2> Functions </h2>
<h3> Preparation </h3>
<p>
<code> int s6dns_hosts_compile (int fdr, int fdw) </code> <br />
Compiles the text file data from file descriptor <tt>fdr</tt>,
which should be in <tt>/etc/hosts</tt> format, into a cdb file
written to file descriptor <tt>fdw</tt>. <tt>fdr</tt> must be
open for reading, and <tt>fdw</tt> must be open for writing and
seekable. The function returns 1 on success and 0 (and sets errno)
on failure.
</p>
<p>
You normally don't need to use this function yourself, because
it's implicitly used by the following one.
</p>
<p>
<code> int s6dns_hosts_init (void) </code> <br />
Initializes the database from the <tt>/etc/hosts</tt> file.
If there's a pre-compiled <tt>/etc/hosts.cdb</tt> file that
is more recent than <tt>/etc/hosts</tt>, then it is used;
else, the <tt>/etc/hosts</tt> file is compiled into a
temporary file under <tt>/tmp</tt>, which is used and
immediately unlinked. The function returns 1 on success and
0 (and sets errno) on failure.
</p>
<p>
<code> int s6dns_hosts_init_r (cdb *c, char const *txtfile, char const *cdbfile, char const *prefix) </code> <br />
The generic version of the above function. Initializes the database
in <em>*c</em> from the compiled file <em>cdbfile</em> if it exists and is
more recent than <em>txtfile</em>, else compiles <em>txtfile</em> into
a temporary file with a path starting with <em>prefix</em>, makes it
accessible in <em>*c</em> and immediately unlinks it.
</p>
<p>
<code> void s6dns_hosts_free (void) </code> <br />
Frees the compiled hosts database. Only use this if
you're certain you'll have no more use for it.
</p>
<p>
<code> void s6dns_hosts_free_r (cdb *c) </code> <br />
The generic version of the above function.
</p>
<h3> IP to name resolution </h3>
<p>
<code> int s6dns_hosts_name_r (cdb const *c, char const *ip, stralloc *storage, genalloc *indices, int is6) </code> <br />
</p>
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