lwres_context.docbook [plain text]
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<refentry>
<refentryinfo>
<date>Jun 30, 2000</date>
</refentryinfo>
<refmeta>
<refentrytitle>lwres_context</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>BIND9</refmiscinfo>
</refmeta>
<docinfo>
<copyright>
<year>2004</year>
<year>2005</year>
<year>2007</year>
<year>2012</year>
<holder>Internet Systems Consortium, Inc. ("ISC")</holder>
</copyright>
<copyright>
<year>2000</year>
<year>2001</year>
<year>2003</year>
<holder>Internet Software Consortium.</holder>
</copyright>
</docinfo>
<refnamediv>
<refname>lwres_context_create</refname>
<refname>lwres_context_destroy</refname>
<refname>lwres_context_nextserial</refname>
<refname>lwres_context_initserial</refname>
<refname>lwres_context_freemem</refname>
<refname>lwres_context_allocmem</refname>
<refname>lwres_context_sendrecv</refname>
<refpurpose>lightweight resolver context management</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <lwres/lwres.h></funcsynopsisinfo>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_context_create</function></funcdef>
<paramdef>lwres_context_t **<parameter>contextp</parameter></paramdef>
<paramdef>void *<parameter>arg</parameter></paramdef>
<paramdef>lwres_malloc_t <parameter>malloc_function</parameter></paramdef>
<paramdef>lwres_free_t <parameter>free_function</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_context_destroy</function></funcdef>
<paramdef>lwres_context_t **<parameter>contextp</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
void
<function>lwres_context_initserial</function></funcdef>
<paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
<paramdef>lwres_uint32_t <parameter>serial</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_uint32_t
<function>lwres_context_nextserial</function></funcdef>
<paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
void
<function>lwres_context_freemem</function></funcdef>
<paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
<paramdef>void *<parameter>mem</parameter></paramdef>
<paramdef>size_t <parameter>len</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
void
<function>lwres_context_allocmem</function></funcdef>
<paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
<paramdef>size_t <parameter>len</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
void *
<function>lwres_context_sendrecv</function></funcdef>
<paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
<paramdef>void *<parameter>sendbase</parameter></paramdef>
<paramdef>int <parameter>sendlen</parameter></paramdef>
<paramdef>void *<parameter>recvbase</parameter></paramdef>
<paramdef>int <parameter>recvlen</parameter></paramdef>
<paramdef>int *<parameter>recvd_len</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>DESCRIPTION</title>
<para><function>lwres_context_create()</function>
creates a <type>lwres_context_t</type> structure for use in
lightweight resolver operations. It holds a socket and other
data needed for communicating with a resolver daemon. The new
<type>lwres_context_t</type> is returned through
<parameter>contextp</parameter>, a pointer to a
<type>lwres_context_t</type> pointer. This
<type>lwres_context_t</type> pointer must initially be NULL, and
is modified to point to the newly created
<type>lwres_context_t</type>.
</para>
<para>
When the lightweight resolver needs to perform dynamic memory
allocation, it will call
<parameter>malloc_function</parameter>
to allocate memory and
<parameter>free_function</parameter>
to free it. If
<parameter>malloc_function</parameter>
and
<parameter>free_function</parameter>
are NULL, memory is allocated using
<citerefentry>
<refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>.
and
<citerefentry>
<refentrytitle>free</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>.
It is not permitted to have a NULL
<parameter>malloc_function</parameter> and a non-NULL
<parameter>free_function</parameter> or vice versa.
<parameter>arg</parameter> is passed as the first parameter to
the memory allocation functions. If
<parameter>malloc_function</parameter> and
<parameter>free_function</parameter> are NULL,
<parameter>arg</parameter> is unused and should be passed as
NULL.
</para>
<para>
Once memory for the structure has been allocated,
it is initialized using
<citerefentry>
<refentrytitle>lwres_conf_init</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>
and returned via <parameter>*contextp</parameter>.
</para>
<para><function>lwres_context_destroy()</function>
destroys a <type>lwres_context_t</type>, closing its socket.
<parameter>contextp</parameter> 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.
</para>
<para>
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
<function>lwres_context_initserial()</function> and
<function>lwres_context_nextserial()</function>.
<function>lwres_context_initserial()</function> sets the serial
number for context <parameter>*ctx</parameter> to
<parameter>serial</parameter>.
<function>lwres_context_nextserial()</function> increments the
serial number and returns the previous value.
</para>
<para>
Memory for a lightweight resolver context is allocated and freed
using <function>lwres_context_allocmem()</function> and
<function>lwres_context_freemem()</function>. These use
whatever allocations were defined when the context was created
with <function>lwres_context_create()</function>.
<function>lwres_context_allocmem()</function> allocates
<parameter>len</parameter> bytes of memory and if successful
returns a pointer to the allocated storage.
<function>lwres_context_freemem()</function> frees
<parameter>len</parameter> bytes of space starting at location
<parameter>mem</parameter>.
</para>
<para><function>lwres_context_sendrecv()</function>
performs I/O for the context <parameter>ctx</parameter>. Data
are read and written from the context's socket. It writes data
from <parameter>sendbase</parameter> — typically a
lightweight resolver query packet — and waits for a reply
which is copied to the receive buffer at
<parameter>recvbase</parameter>. The number of bytes that were
written to this receive buffer is returned in
<parameter>*recvd_len</parameter>.
</para>
</refsect1>
<refsect1>
<title>RETURN VALUES</title>
<para><function>lwres_context_create()</function>
returns <errorcode>LWRES_R_NOMEMORY</errorcode> if memory for
the <type>struct lwres_context</type> could not be allocated,
<errorcode>LWRES_R_SUCCESS</errorcode> otherwise.
</para>
<para>
Successful calls to the memory allocator
<function>lwres_context_allocmem()</function>
return a pointer to the start of the allocated space.
It returns NULL if memory could not be allocated.
</para>
<para><errorcode>LWRES_R_SUCCESS</errorcode>
is returned when
<function>lwres_context_sendrecv()</function>
completes successfully.
<errorcode>LWRES_R_IOERROR</errorcode>
is returned if an I/O error occurs and
<errorcode>LWRES_R_TIMEOUT</errorcode>
is returned if
<function>lwres_context_sendrecv()</function>
times out waiting for a response.
</para>
</refsect1>
<refsect1>
<title>SEE ALSO</title>
<para><citerefentry>
<refentrytitle>lwres_conf_init</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>free</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>.
</para>
</refsect1>
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