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<title>lwres_context</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
<a name="id2476275"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>lwres_context_create, lwres_context_destroy, lwres_context_nextserial, lwres_context_initserial, lwres_context_freemem, lwres_context_allocmem, lwres_context_sendrecv — lightweight resolver context management</p>
</div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="funcsynopsis">
<pre class="funcsynopsisinfo">#include <lwres/lwres.h></pre>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_context_create</b>(</code></td>
<td>lwres_context_t ** </td>
<td>
<var class="pdparam">contextp</var>, </td>
</tr>
<tr>
<td> </td>
<td>void * </td>
<td>
<var class="pdparam">arg</var>, </td>
</tr>
<tr>
<td> </td>
<td>lwres_malloc_t </td>
<td>
<var class="pdparam">malloc_function</var>, </td>
</tr>
<tr>
<td> </td>
<td>lwres_free_t </td>
<td>
<var class="pdparam">free_function</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_context_destroy</b>(</code></td>
<td>lwres_context_t ** </td>
<td>
<var class="pdparam">contextp</var><code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_context_initserial</b>(</code></td>
<td>lwres_context_t * </td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td> </td>
<td>lwres_uint32_t </td>
<td>
<var class="pdparam">serial</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
lwres_uint32_t
<b class="fsfunc">lwres_context_nextserial</b>(</code></td>
<td>lwres_context_t * </td>
<td>
<var class="pdparam">ctx</var><code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_context_freemem</b>(</code></td>
<td>lwres_context_t * </td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td> </td>
<td>void * </td>
<td>
<var class="pdparam">mem</var>, </td>
</tr>
<tr>
<td> </td>
<td>size_t </td>
<td>
<var class="pdparam">len</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_context_allocmem</b>(</code></td>
<td>lwres_context_t * </td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td> </td>
<td>size_t </td>
<td>
<var class="pdparam">len</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
<tr>
<td><code class="funcdef">
void *
<b class="fsfunc">lwres_context_sendrecv</b>(</code></td>
<td>lwres_context_t * </td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td> </td>
<td>void * </td>
<td>
<var class="pdparam">sendbase</var>, </td>
</tr>
<tr>
<td> </td>
<td>int </td>
<td>
<var class="pdparam">sendlen</var>, </td>
</tr>
<tr>
<td> </td>
<td>void * </td>
<td>
<var class="pdparam">recvbase</var>, </td>
</tr>
<tr>
<td> </td>
<td>int </td>
<td>
<var class="pdparam">recvlen</var>, </td>
</tr>
<tr>
<td> </td>
<td>int * </td>
<td>
<var class="pdparam">recvd_len</var><code>)</code>;</td>
</tr>
</table>
</div>
</div>
<div class="refsect1" lang="en">
<a name="id2543536"></a><h2>DESCRIPTION</h2>
<p><code class="function">lwres_context_create()</code>
creates a <span class="type">lwres_context_t</span> structure for use in
lightweight resolver operations. It holds a socket and other
data needed for communicating with a resolver daemon. The new
<span class="type">lwres_context_t</span> is returned through
<em class="parameter"><code>contextp</code></em>, a pointer to a
<span class="type">lwres_context_t</span> pointer. This
<span class="type">lwres_context_t</span> pointer must initially be NULL, and
is modified to point to the newly created
<span class="type">lwres_context_t</span>.
</p>
<p>
When the lightweight resolver needs to perform dynamic memory
allocation, it will call
<em class="parameter"><code>malloc_function</code></em>
to allocate memory and
<em class="parameter"><code>free_function</code></em>
to free it. If
<em class="parameter"><code>malloc_function</code></em>
and
<em class="parameter"><code>free_function</code></em>
are NULL, memory is allocated using
<span class="citerefentry"><span class="refentrytitle">malloc</span>(3)</span>.
and
<span class="citerefentry"><span class="refentrytitle">free</span>(3)</span>.
It is not permitted to have a NULL
<em class="parameter"><code>malloc_function</code></em> and a non-NULL
<em class="parameter"><code>free_function</code></em> or vice versa.
<em class="parameter"><code>arg</code></em> is passed as the first parameter to
the memory allocation functions. If
<em class="parameter"><code>malloc_function</code></em> and
<em class="parameter"><code>free_function</code></em> are NULL,
<em class="parameter"><code>arg</code></em> is unused and should be passed as
NULL.
</p>
<p>
Once memory for the structure has been allocated,
it is initialized using
<span class="citerefentry"><span class="refentrytitle">lwres_conf_init</span>(3)</span>
and returned via <em class="parameter"><code>*contextp</code></em>.
</p>
<p><code class="function">lwres_context_destroy()</code>
destroys a <span class="type">lwres_context_t</span>, closing its socket.
<em class="parameter"><code>contextp</code></em> is a pointer to a pointer to the
context that is to be destroyed. The pointer will be set to
NULL when the context has been destroyed.
</p>
<p>
The context holds a serial number that is used to identify
resolver request packets and associate responses with the
corresponding requests. This serial number is controlled using
<code class="function">lwres_context_initserial()</code> and
<code class="function">lwres_context_nextserial()</code>.
<code class="function">lwres_context_initserial()</code> sets the serial
number for context <em class="parameter"><code>*ctx</code></em> to
<em class="parameter"><code>serial</code></em>.
<code class="function">lwres_context_nextserial()</code> increments the
serial number and returns the previous value.
</p>
<p>
Memory for a lightweight resolver context is allocated and freed
using <code class="function">lwres_context_allocmem()</code> and
<code class="function">lwres_context_freemem()</code>. These use
whatever allocations were defined when the context was created
with <code class="function">lwres_context_create()</code>.
<code class="function">lwres_context_allocmem()</code> allocates
<em class="parameter"><code>len</code></em> bytes of memory and if successful
returns a pointer to the allocated storage.
<code class="function">lwres_context_freemem()</code> frees
<em class="parameter"><code>len</code></em> bytes of space starting at location
<em class="parameter"><code>mem</code></em>.
</p>
<p><code class="function">lwres_context_sendrecv()</code>
performs I/O for the context <em class="parameter"><code>ctx</code></em>. Data
are read and written from the context's socket. It writes data
from <em class="parameter"><code>sendbase</code></em> — typically a
lightweight resolver query packet — and waits for a reply
which is copied to the receive buffer at
<em class="parameter"><code>recvbase</code></em>. The number of bytes that were
written to this receive buffer is returned in
<em class="parameter"><code>*recvd_len</code></em>.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2543723"></a><h2>RETURN VALUES</h2>
<p><code class="function">lwres_context_create()</code>
returns <span class="errorcode">LWRES_R_NOMEMORY</span> if memory for
the <span class="type">struct lwres_context</span> could not be allocated,
<span class="errorcode">LWRES_R_SUCCESS</span> otherwise.
</p>
<p>
Successful calls to the memory allocator
<code class="function">lwres_context_allocmem()</code>
return a pointer to the start of the allocated space.
It returns NULL if memory could not be allocated.
</p>
<p><span class="errorcode">LWRES_R_SUCCESS</span>
is returned when
<code class="function">lwres_context_sendrecv()</code>
completes successfully.
<span class="errorcode">LWRES_R_IOERROR</span>
is returned if an I/O error occurs and
<span class="errorcode">LWRES_R_TIMEOUT</span>
is returned if
<code class="function">lwres_context_sendrecv()</code>
times out waiting for a response.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2543773"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry"><span class="refentrytitle">lwres_conf_init</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">malloc</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">free</span>(3)</span>.
</p>
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