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<title>lwres_resutil</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry">
<a name="id-1"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>
lwres_string_parse,
lwres_addr_parse,
lwres_getaddrsbyname,
lwres_getnamebyaddr
— lightweight resolver utility functions
</p>
</div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="funcsynopsis">
<pre class="funcsynopsisinfo">#include <lwres/lwres.h></pre>
<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_string_parse</b>(</code></td>
<td>lwres_buffer_t *<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td> </td>
<td>char **<var class="pdparam">c</var>, </td>
</tr>
<tr>
<td> </td>
<td>uint16_t *<var class="pdparam">len</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_addr_parse</b>(</code></td>
<td>lwres_buffer_t *<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td> </td>
<td>lwres_addr_t *<var class="pdparam">addr</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_getaddrsbyname</b>(</code></td>
<td>lwres_context_t *<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td> </td>
<td>const char *<var class="pdparam">name</var>, </td>
</tr>
<tr>
<td> </td>
<td>uint32_t <var class="pdparam">addrtypes</var>, </td>
</tr>
<tr>
<td> </td>
<td>lwres_gabnresponse_t **<var class="pdparam">structp</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_getnamebyaddr</b>(</code></td>
<td>lwres_context_t *<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td> </td>
<td>uint32_t <var class="pdparam">addrtype</var>, </td>
</tr>
<tr>
<td> </td>
<td>uint16_t <var class="pdparam">addrlen</var>, </td>
</tr>
<tr>
<td> </td>
<td>const unsigned char *<var class="pdparam">addr</var>, </td>
</tr>
<tr>
<td> </td>
<td>lwres_gnbaresponse_t **<var class="pdparam">structp</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
</div>
</div>
<div class="refsection">
<a name="id-1.7"></a><h2>DESCRIPTION</h2>
<p><code class="function">lwres_string_parse()</code>
retrieves a DNS-encoded string starting the current pointer of
lightweight resolver buffer <em class="parameter"><code>b</code></em>: i.e.
<code class="constant">b->current</code>. When the function returns,
the address of the first byte of the encoded string is returned
via <em class="parameter"><code>*c</code></em> and the length of that string is
given by <em class="parameter"><code>*len</code></em>. The buffer's current
pointer is advanced to point at the character following the
string length, the encoded string, and the trailing
<span class="type">NULL</span> character.
</p>
<p><code class="function">lwres_addr_parse()</code>
extracts an address from the buffer <em class="parameter"><code>b</code></em>.
The buffer's current pointer <code class="constant">b->current</code>
is presumed to point at an encoded address: the address preceded
by a 32-bit protocol family identifier and a 16-bit length
field. The encoded address is copied to
<code class="constant">addr->address</code> and
<code class="constant">addr->length</code> indicates the size in bytes
of the address that was copied.
<code class="constant">b->current</code> is advanced to point at the
next byte of available data in the buffer following the encoded
address.
</p>
<p><code class="function">lwres_getaddrsbyname()</code>
and <code class="function">lwres_getnamebyaddr()</code> use the
<span class="type">lwres_gnbaresponse_t</span> structure defined below:
</p>
<pre class="programlisting">
typedef struct {
uint32_t flags;
uint16_t naliases;
uint16_t naddrs;
char *realname;
char **aliases;
uint16_t realnamelen;
uint16_t *aliaslen;
lwres_addrlist_t addrs;
void *base;
size_t baselen;
} lwres_gabnresponse_t;
</pre>
<p>
The contents of this structure are not manipulated directly but
they are controlled through the
<span class="citerefentry">
<span class="refentrytitle">lwres_gabn</span>(3)
</span>
functions.
</p>
<p>
The lightweight resolver uses
<code class="function">lwres_getaddrsbyname()</code> to perform
forward lookups.
Hostname <em class="parameter"><code>name</code></em> is looked up using the
resolver
context <em class="parameter"><code>ctx</code></em> for memory allocation.
<em class="parameter"><code>addrtypes</code></em> is a bitmask indicating
which type of
addresses are to be looked up. Current values for this bitmask are
<span class="type">LWRES_ADDRTYPE_V4</span> for IPv4 addresses and
<span class="type">LWRES_ADDRTYPE_V6</span> for IPv6 addresses. Results of the
lookup are returned in <em class="parameter"><code>*structp</code></em>.
</p>
<p><code class="function">lwres_getnamebyaddr()</code>
performs reverse lookups. Resolver context
<em class="parameter"><code>ctx</code></em> is used for memory allocation. The
address type is indicated by <em class="parameter"><code>addrtype</code></em>:
<span class="type">LWRES_ADDRTYPE_V4</span> or
<span class="type">LWRES_ADDRTYPE_V6</span>. The address to be looked up is
given by <em class="parameter"><code>addr</code></em> and its length is
<em class="parameter"><code>addrlen</code></em> bytes. The result of the
function call is made available through
<em class="parameter"><code>*structp</code></em>.
</p>
</div>
<div class="refsection">
<a name="id-1.8"></a><h2>RETURN VALUES</h2>
<p>
Successful calls to
<code class="function">lwres_string_parse()</code>
and
<code class="function">lwres_addr_parse()</code>
return
<span class="errorcode">LWRES_R_SUCCESS.</span>
Both functions return
<span class="errorcode">LWRES_R_FAILURE</span>
if the buffer is corrupt or
<span class="errorcode">LWRES_R_UNEXPECTEDEND</span>
if the buffer has less space than expected for the components of the
encoded string or address.
</p>
<p><code class="function">lwres_getaddrsbyname()</code>
returns <span class="errorcode">LWRES_R_SUCCESS</span> on success and it
returns <span class="errorcode">LWRES_R_NOTFOUND</span> if the hostname
<em class="parameter"><code>name</code></em> could not be found.
</p>
<p><span class="errorcode">LWRES_R_SUCCESS</span>
is returned by a successful call to
<code class="function">lwres_getnamebyaddr()</code>.
</p>
<p>
Both
<code class="function">lwres_getaddrsbyname()</code>
and
<code class="function">lwres_getnamebyaddr()</code>
return
<span class="errorcode">LWRES_R_NOMEMORY</span>
when memory allocation requests fail and
<span class="errorcode">LWRES_R_UNEXPECTEDEND</span>
if the buffers used for sending queries and receiving replies are too
small.
</p>
</div>
<div class="refsection">
<a name="id-1.9"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry">
<span class="refentrytitle">lwres_buffer</span>(3)
</span>,
<span class="citerefentry">
<span class="refentrytitle">lwres_gabn</span>(3)
</span>.
</p>
</div>
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