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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>
      <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 *ctx</paramdef>
<paramdef>lwres_nooprequest_t *req</paramdef>
<paramdef>lwres_lwpacket_t *pkt</paramdef>
<paramdef>lwres_buffer_t *b</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_noopresponse_render</function></funcdef>
<paramdef>lwres_context_t *ctx</paramdef>
<paramdef>lwres_noopresponse_t *req</paramdef>
<paramdef>lwres_lwpacket_t *pkt</paramdef>
<paramdef>lwres_buffer_t *b</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_nooprequest_parse</function></funcdef>
<paramdef>lwres_context_t *ctx</paramdef>
<paramdef>lwres_buffer_t *b</paramdef>
<paramdef>lwres_lwpacket_t *pkt</paramdef>
<paramdef>lwres_nooprequest_t **structp</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_noopresponse_parse</function></funcdef>
<paramdef>lwres_context_t *ctx</paramdef>
<paramdef>lwres_buffer_t *b</paramdef>
<paramdef>lwres_lwpacket_t *pkt</paramdef>
<paramdef>lwres_noopresponse_t **structp</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
void
<function>lwres_noopresponse_free</function></funcdef>
<paramdef>lwres_context_t *ctx</paramdef>
<paramdef>lwres_noopresponse_t **structp</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
void
<function>lwres_nooprequest_free</function></funcdef>
<paramdef>lwres_context_t *ctx</paramdef>
<paramdef>lwres_nooprequest_t **structp</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.
<programlisting>
#define LWRES_OPCODE_NOOP       0x00000000U

typedef struct {
        lwres_uint16_t  datalength;
        unsigned char   *data;
} lwres_nooprequest_t;

typedef struct {
        lwres_uint16_t  datalength;
        unsigned char   *data;
} lwres_noopresponse_t;
</programlisting>
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>
</refentry>
