lwres_noop.html revision ac299c4f5ca236370b9df2a91b18b149b1d344a7
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<HTML
><HEAD
><TITLE
>lwres_noop</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.61
"></HEAD
><BODY
CLASS="REFENTRY"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><H1
><A
NAME="AEN1"
>lwres_noop</A
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8"
></A
><H2
>Name</H2
>lwres_nooprequest_render, lwres_noopresponse_render, lwres_nooprequest_parse, lwres_noopresponse_parse, lwres_noopresponse_free, lwres_nooprequest_free -- lightweight resolver no-op message handling</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN16"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN17"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_nooprequest_render</CODE
>(lwres_context_t *ctx, lwres_nooprequest_t *req, lwres_lwpacket_t *pkt, lwres_buffer_t *b);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_noopresponse_render</CODE
>(lwres_context_t *ctx, lwres_noopresponse_t *req, lwres_lwpacket_t *pkt, lwres_buffer_t *b);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_nooprequest_parse</CODE
>(lwres_context_t *ctx, lwres_buffer_t *b, lwres_lwpacket_t *pkt, lwres_nooprequest_t **structp);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_noopresponse_parse</CODE
>(lwres_context_t *ctx, lwres_buffer_t *b, lwres_lwpacket_t *pkt, lwres_noopresponse_t **structp);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_noopresponse_free</CODE
>(lwres_context_t *ctx, lwres_noopresponse_t **structp);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_nooprequest_free</CODE
>(lwres_context_t *ctx, lwres_nooprequest_t **structp);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN57"
></A
><H2
>DESCRIPTION</H2
><P
>These are low-level routines for creating and parsing
lightweight resolver no-op request and response messages.</P
><P
>The no-op message is analogous to a <B
CLASS="COMMAND"
>ping</B
> 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.</P
><P
>There are four main functions for the no-op opcode.
One render function converts a no-op request structure —
<SPAN
CLASS="TYPE"
>lwres_nooprequest_t</SPAN
> —
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 —
<SPAN
CLASS="TYPE"
>lwres_noopresponse_t</SPAN
>
to the canonical format.
This is complemented by a parse function which converts a packet in
canonical format to a no-op response structure.</P
><P
>These structures are defined in
<TT
CLASS="FILENAME"
>.
They are shown below.
<PRE
CLASS="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;</PRE
>
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.</P
><P
><TT
CLASS="FUNCTION"
>lwres_nooprequest_render()</TT
> uses resolver
context <TT
CLASS="PARAMETER"
><I
>ctx</I
></TT
> to convert no-op request structure
<TT
CLASS="PARAMETER"
><I
>req</I
></TT
> to canonical format. The packet header
structure <TT
CLASS="PARAMETER"
><I
>pkt</I
></TT
> is initialised and transferred to
buffer <TT
CLASS="PARAMETER"
><I
>b</I
></TT
>. The contents of
<TT
CLASS="PARAMETER"
><I
>*req</I
></TT
> are then appended to the buffer in
canonical format. <TT
CLASS="FUNCTION"
>lwres_noopresponse_render()</TT
>
performs the same task, except it converts a no-op response structure
<SPAN
CLASS="TYPE"
>lwres_noopresponse_t</SPAN
> to the lightweight resolver's
canonical format.</P
><P
><TT
CLASS="FUNCTION"
>lwres_nooprequest_parse()</TT
> uses context
<TT
CLASS="PARAMETER"
><I
>ctx</I
></TT
> to convert the contents of packet
<TT
CLASS="PARAMETER"
><I
>pkt</I
></TT
> to a <SPAN
CLASS="TYPE"
>lwres_nooprequest_t</SPAN
>
structure. Buffer <TT
CLASS="PARAMETER"
><I
>b</I
></TT
> provides space to be used
for storing this structure. When the function succeeds, the resulting
<SPAN
CLASS="TYPE"
>lwres_nooprequest_t</SPAN
> is made available through
<TT
CLASS="PARAMETER"
><I
>*structp</I
></TT
>.
<TT
CLASS="FUNCTION"
>lwres_noopresponse_parse()</TT
> offers the same
semantics as <TT
CLASS="FUNCTION"
>lwres_nooprequest_parse()</TT
> except it
yields a <SPAN
CLASS="TYPE"
>lwres_noopresponse_t</SPAN
> structure.</P
><P
><TT
CLASS="FUNCTION"
>lwres_noopresponse_free()</TT
> and
<TT
CLASS="FUNCTION"
>lwres_nooprequest_free()</TT
> release the memory in
resolver context <TT
CLASS="PARAMETER"
><I
>ctx</I
></TT
> that was allocated to the
<SPAN
CLASS="TYPE"
>lwres_noopresponse_t</SPAN
> or <SPAN
CLASS="TYPE"
>lwres_nooprequest_t</SPAN
>
structures referenced via <TT
CLASS="PARAMETER"
><I
>structp</I
></TT
>.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN95"
></A
><H2
>RETURN VALUES</H2
><P
>The no-op opcode functions
<TT
CLASS="FUNCTION"
>lwres_nooprequest_render()</TT
>,
<TT
CLASS="FUNCTION"
>lwres_noopresponse_render()</TT
>
<TT
CLASS="FUNCTION"
>lwres_nooprequest_parse()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_noopresponse_parse()</TT
>
all return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_SUCCESS</SPAN
>
on success.
They return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_NOMEMORY</SPAN
>
if memory allocation fails.
<SPAN
CLASS="ERRORCODE"
>LWRES_R_UNEXPECTEDEND</SPAN
>
is returned if the available space in the buffer
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>
is too small to accommodate the packet header or the
<SPAN
CLASS="TYPE"
>lwres_nooprequest_t</SPAN
>
and
<SPAN
CLASS="TYPE"
>lwres_noopresponse_t</SPAN
>
structures.
<TT
CLASS="FUNCTION"
>lwres_nooprequest_parse()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_noopresponse_parse()</TT
>
will return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_UNEXPECTEDEND</SPAN
>
if the buffer is not empty after decoding the received packet.
These functions will return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_FAILURE</SPAN
>
if
<TT
CLASS="CONSTANT"
>pktflags</TT
>
in the packet header structure
<SPAN
CLASS="TYPE"
>lwres_lwpacket_t</SPAN
>
indicate that the packet is not a response to an earlier query.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN114"
></A
><H2
>SEE ALSO</H2
><P
><SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>lwres_packet</SPAN
>(3)</SPAN
></P
></DIV
></BODY
></HTML
>