lwres_context.docbook

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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>
      <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 &lt;lwres/lwres.h&gt;</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> &mdash; typically a
      lightweight resolver query packet &mdash; 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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