lwres_noop.docbook

非常好的dns解析软件

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<refentry>

  <refentryinfo>
    <date>Jun 30, 2000</date>
  </refentryinfo>

  <refmeta>
    <refentrytitle>lwres_noop</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>
      <holder>Internet Software Consortium.</holder>
    </copyright>
  </docinfo>

  <refnamediv>
    <refname>lwres_nooprequest_render</refname>
    <refname>lwres_noopresponse_render</refname>
    <refname>lwres_nooprequest_parse</refname>
    <refname>lwres_noopresponse_parse</refname>
    <refname>lwres_noopresponse_free</refname>
    <refname>lwres_nooprequest_free</refname>
    <refpurpose>lightweight resolver no-op message handling</refpurpose>
  </refnamediv>
  <refsynopsisdiv>
    <funcsynopsis>
<funcsynopsisinfo>
#include &lt;lwres/lwres.h&gt;</funcsynopsisinfo>
<funcprototype>
        <funcdef>
lwres_result_t
<function>lwres_nooprequest_render</function></funcdef>
        <paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
        <paramdef>lwres_nooprequest_t *<parameter>req</parameter></paramdef>
        <paramdef>lwres_lwpacket_t *<parameter>pkt</parameter></paramdef>
        <paramdef>lwres_buffer_t *<parameter>b</parameter></paramdef>
        </funcprototype>
<funcprototype>
        <funcdef>
lwres_result_t
<function>lwres_noopresponse_render</function></funcdef>
        <paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
        <paramdef>lwres_noopresponse_t *<parameter>req</parameter></paramdef>
        <paramdef>lwres_lwpacket_t *<parameter>pkt</parameter></paramdef>
        <paramdef>lwres_buffer_t *<parameter>b</parameter></paramdef>
        </funcprototype>
<funcprototype>
        <funcdef>
lwres_result_t
<function>lwres_nooprequest_parse</function></funcdef>
        <paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
        <paramdef>lwres_buffer_t *<parameter>b</parameter></paramdef>
        <paramdef>lwres_lwpacket_t *<parameter>pkt</parameter></paramdef>
        <paramdef>lwres_nooprequest_t **<parameter>structp</parameter></paramdef>
        </funcprototype>
<funcprototype>
        <funcdef>
lwres_result_t
<function>lwres_noopresponse_parse</function></funcdef>
        <paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
        <paramdef>lwres_buffer_t *<parameter>b</parameter></paramdef>
        <paramdef>lwres_lwpacket_t *<parameter>pkt</parameter></paramdef>
        <paramdef>lwres_noopresponse_t **<parameter>structp</parameter></paramdef>
        </funcprototype>
<funcprototype>
        <funcdef>
void
<function>lwres_noopresponse_free</function></funcdef>
        <paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
        <paramdef>lwres_noopresponse_t **<parameter>structp</parameter></paramdef>
        </funcprototype>
<funcprototype>
        <funcdef>
void
<function>lwres_nooprequest_free</function></funcdef>
        <paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
        <paramdef>lwres_nooprequest_t **<parameter>structp</parameter></paramdef>
      </funcprototype>
</funcsynopsis>
  </refsynopsisdiv>
  <refsect1>
    <title>DESCRIPTION</title>
    <para>
      These are low-level routines for creating and parsing
      lightweight resolver no-op request and response messages.
    </para>
    <para>
      The no-op message is analogous to a <command>ping</command>
      packet:
      a packet is sent to the resolver daemon and is simply echoed back.
      The opcode is intended to allow a client to determine if the server is
      operational or not.
    </para>
    <para>
      There are four main functions for the no-op opcode.
      One render function converts a no-op request structure &mdash;
      <type>lwres_nooprequest_t</type> &mdash;
      to the lighweight resolver's canonical format.
      It is complemented by a parse function that converts a packet in this
      canonical format to a no-op request structure.
      Another render function converts the no-op response structure &mdash;
      <type>lwres_noopresponse_t</type>
      to the canonical format.
      This is complemented by a parse function which converts a packet in
      canonical format to a no-op response structure.
    </para>
    <para>
      These structures are defined in
      <filename>lwres/lwres.h</filename>.

      They are shown below.
    </para>
    <para><programlisting>
#define LWRES_OPCODE_NOOP       0x00000000U
</programlisting>
    </para>
    <para><programlisting>
typedef struct {
        lwres_uint16_t  datalength;
        unsigned char   *data;
} lwres_nooprequest_t;
</programlisting>
    </para>
    <para><programlisting>
typedef struct {
        lwres_uint16_t  datalength;
        unsigned char   *data;
} lwres_noopresponse_t;
</programlisting>
    </para>
    <para>
      Although the structures have different types, they are identical.
      This is because the no-op opcode simply echos whatever data was sent:
      the response is therefore identical to the request.
    </para>

    <para><function>lwres_nooprequest_render()</function>
      uses resolver context <parameter>ctx</parameter> to convert
      no-op request structure <parameter>req</parameter> to canonical
      format.  The packet header structure <parameter>pkt</parameter>
      is initialised and transferred to buffer
      <parameter>b</parameter>.  The contents of
      <parameter>*req</parameter> are then appended to the buffer in
      canonical format.
      <function>lwres_noopresponse_render()</function> performs the
      same task, except it converts a no-op response structure
      <type>lwres_noopresponse_t</type> to the lightweight resolver's
      canonical format.
    </para>

    <para><function>lwres_nooprequest_parse()</function>
      uses context <parameter>ctx</parameter> to convert the contents
      of packet <parameter>pkt</parameter> to a
      <type>lwres_nooprequest_t</type> structure.  Buffer
      <parameter>b</parameter> provides space to be used for storing
      this structure.  When the function succeeds, the resulting
      <type>lwres_nooprequest_t</type> is made available through
      <parameter>*structp</parameter>.
      <function>lwres_noopresponse_parse()</function> offers the same
      semantics as <function>lwres_nooprequest_parse()</function>
      except it yields a <type>lwres_noopresponse_t</type> structure.
    </para>

    <para><function>lwres_noopresponse_free()</function>
      and <function>lwres_nooprequest_free()</function> release the
      memory in resolver context <parameter>ctx</parameter> that was
      allocated to the <type>lwres_noopresponse_t</type> or
      <type>lwres_nooprequest_t</type> structures referenced via
      <parameter>structp</parameter>.
    </para>

  </refsect1>
  <refsect1>
    <title>RETURN VALUES</title>
    <para>
      The no-op opcode functions
      <function>lwres_nooprequest_render()</function>,

      <function>lwres_noopresponse_render()</function>
      <function>lwres_nooprequest_parse()</function>
      and
      <function>lwres_noopresponse_parse()</function>
      all return
      <errorcode>LWRES_R_SUCCESS</errorcode>
      on success.
      They return
      <errorcode>LWRES_R_NOMEMORY</errorcode>
      if memory allocation fails.
      <errorcode>LWRES_R_UNEXPECTEDEND</errorcode>
      is returned if the available space in the buffer
      <parameter>b</parameter>
      is too small to accommodate the packet header or the
      <type>lwres_nooprequest_t</type>
      and
      <type>lwres_noopresponse_t</type>
      structures.
      <function>lwres_nooprequest_parse()</function>
      and
      <function>lwres_noopresponse_parse()</function>
      will return
      <errorcode>LWRES_R_UNEXPECTEDEND</errorcode>
      if the buffer is not empty after decoding the received packet.
      These functions will return
      <errorcode>LWRES_R_FAILURE</errorcode>
      if
      <constant>pktflags</constant>
      in the packet header structure
      <type>lwres_lwpacket_t</type>
      indicate that the packet is not a response to an earlier query.
    </para>
  </refsect1>
  <refsect1>
    <title>SEE ALSO</title>
    <para><citerefentry>
        <refentrytitle>lwres_packet</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>
    </para>
  </refsect1>
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