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b3d0736ce9ff54f95fc06741c7279172f961363fshankar_mbn<HTML
b3d0736ce9ff54f95fc06741c7279172f961363fshankar_mbn><HEAD
><TITLE
>lwres_resutil</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_resutil</A
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8"
></A
><H2
>Name</H2
>lwres_string_parse, lwres_addr_parse, lwres_getaddrsbyname, lwres_getnamebyaddr&nbsp;--&nbsp;lightweight resolver utility functions</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN14"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN15"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include &lt;lwres/lwres.h&gt;</PRE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_string_parse</CODE
>(lwres_buffer_t *b, char **c, lwres_uint16_t *len);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_addr_parse</CODE
>(lwres_buffer_t *b, lwres_addr_t *addr);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_getaddrsbyname</CODE
>(lwres_context_t *ctx, const char *name, lwres_uint32_t addrtypes, lwres_gabnresponse_t **structp);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_getnamebyaddr</CODE
>(lwres_context_t *ctx, lwres_uint32_t addrtype, lwres_uint16_t addrlen, const unsigned char *addr, lwres_gnbaresponse_t **structp);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN43"
></A
><H2
>DESCRIPTION</H2
><P
><TT
CLASS="FUNCTION"
>lwres_string_parse()</TT
>
retrieves a DNS-encoded string starting the current pointer of
lightweight resolver buffer
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>:
i.e.
<TT
CLASS="CONSTANT"
>b-&gt;current</TT
>.
When the function returns, the address of the first byte of the
encoded string is returned via
<TT
CLASS="PARAMETER"
><I
>*c</I
></TT
>
and the length of that string is given by
<TT
CLASS="PARAMETER"
><I
>*len</I
></TT
>.
The buffer's current pointer is advanced to point at the character
following the string length, the encoded string, and the trailing
<SPAN
CLASS="TYPE"
>NULL</SPAN
>
character.
<TT
CLASS="FUNCTION"
>lwres_string_parse()</TT
>
has an assertion check that
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>
is not
<SPAN
CLASS="TYPE"
>NULL</SPAN
>.&#13;</P
><P
><TT
CLASS="FUNCTION"
>lwres_addr_parse()</TT
>
extracts an address from the buffer
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>.
It checks that
<TT
CLASS="PARAMETER"
><I
>addr</I
></TT
>
is not null.
The buffer's current pointer
<TT
CLASS="CONSTANT"
>b-&gt;current</TT
>
is presumed to point at an encoded address: the address preceded by a
32-bit protocol family identifier and a 16-bit length field.
The encoded address is copied to
<TT
CLASS="CONSTANT"
>addr-&gt;address</TT
>
and
<TT
CLASS="CONSTANT"
>addr-&gt;length</TT
>
indicates the size in bytes of the address that was copied.
<TT
CLASS="CONSTANT"
>b-&gt;current</TT
>
is advanced to point at the next byte of available data in the buffer
following the encoded address.</P
><P
><TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>
use the
<SPAN
CLASS="TYPE"
>lwres_gnbaresponse_t</SPAN
>
structure defined below:
<PRE
CLASS="PROGRAMLISTING"
>typedef struct {
lwres_uint32_t flags;
lwres_uint16_t naliases;
lwres_uint16_t naddrs;
char *realname;
char **aliases;
lwres_uint16_t realnamelen;
lwres_uint16_t *aliaslen;
lwres_addrlist_t addrs;
void *base;
size_t baselen;
} lwres_gabnresponse_t;</PRE
>
The contents of this structure are not manipulated directly but
they are controlled through the
<SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>lwres_gabn</SPAN
>(3)</SPAN
>
functions.</P
><P
>The lightweight resolver uses
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
to perform foward lookups.
Hostname
<TT
CLASS="PARAMETER"
><I
>name</I
></TT
>
is looked up using the resolver context
<TT
CLASS="PARAMETER"
><I
>ctx</I
></TT
>
for memory allocation.
<TT
CLASS="PARAMETER"
><I
>addrtypes</I
></TT
>
is a bitmask indicating which type of addresses are to be looked up.
Current values for this bitmask are
<SPAN
CLASS="TYPE"
>LWRES_ADDRTYPE_V4</SPAN
>
for IPv4 addresses and
<SPAN
CLASS="TYPE"
>LWRES_ADDRTYPE_V6</SPAN
>
for IPv6 addresses.
Results of the lookup are returned in
<TT
CLASS="PARAMETER"
><I
>*structp</I
></TT
>.
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
checks that its pointer arguments are not
<SPAN
CLASS="TYPE"
>NULL</SPAN
>
and that
<TT
CLASS="PARAMETER"
><I
>addrtypes</I
></TT
>
is non-zero.</P
><P
><TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>
performs reverse lookups.
Resolver context
<TT
CLASS="PARAMETER"
><I
>ctx</I
></TT
>
is used for memory allocation.
The address type is indicated by
<TT
CLASS="PARAMETER"
><I
>addrtype</I
></TT
>:
<SPAN
CLASS="TYPE"
>LWRES_ADDRTYPE_V4</SPAN
>
or
<SPAN
CLASS="TYPE"
>LWRES_ADDRTYPE_V6</SPAN
>.
The address to be looked up is given by
<TT
CLASS="PARAMETER"
><I
>addr</I
></TT
>
and its length is
<TT
CLASS="PARAMETER"
><I
>addrlen</I
></TT
>
bytes.
The result of the function call is made available through
<TT
CLASS="PARAMETER"
><I
>*structp</I
></TT
>.
Like
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>,
<TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>
uses assertion checking to ensure its pointer arguments are not
<SPAN
CLASS="TYPE"
>NULL</SPAN
>
and
<TT
CLASS="PARAMETER"
><I
>addrtype</I
></TT
>
is not zero.
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
also checks that
<TT
CLASS="PARAMETER"
><I
>addrlen</I
></TT
>
is non-zero.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN97"
></A
><H2
>RETURN VALUES</H2
><P
>Successful calls to
<TT
CLASS="FUNCTION"
>lwres_string_parse()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_addr_parse()</TT
>
return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_SUCCESS.</SPAN
>
Both functions return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_FAILURE</SPAN
>
if the buffer is corrupt or
<SPAN
CLASS="ERRORCODE"
>LWRES_R_UNEXPECTEDEND</SPAN
>
if the buffer has less space than expected for the components of the
encoded string or address.</P
><P
><TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
returns
<SPAN
CLASS="ERRORCODE"
>LWRES_R_SUCCESS</SPAN
>
on success and it returns
<SPAN
CLASS="ERRORCODE"
>LWRES_R_NOTFOUND</SPAN
>
if the hostname
<TT
CLASS="PARAMETER"
><I
>name</I
></TT
>
could not be found.</P
><P
><SPAN
CLASS="ERRORCODE"
>LWRES_R_SUCCESS</SPAN
>
is returned by a successful call to
<TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>.&#13;</P
><P
>Both
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>
return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_NOMEMORY</SPAN
>
when memory allocation requests fail and
<SPAN
CLASS="ERRORCODE"
>LWRES_R_UNEXPECTEDEND</SPAN
>
if the buffers used for sending queries and receiving replies are too
small.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN118"
></A
><H2
>SEE ALSO</H2
><P
><SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>lwres_buffer</SPAN
>(3)</SPAN
>,
<SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>lwres_gabn</SPAN
>(3)</SPAN
>.</P
></DIV
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>