lwres_resutil.docbook

openswan

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<refentry>

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

<refmeta>
  <refentrytitle>lwres_resutil</refentrytitle>
  <manvolnum>3</manvolnum>
  <refmiscinfo>BIND9</refmiscinfo>
</refmeta>

<refnamediv>
<refname>lwres_string_parse</refname>
<refname>lwres_addr_parse</refname>
<refname>lwres_getaddrsbyname</refname>
<refname>lwres_getnamebyaddr</refname>
<refpurpose>lightweight resolver utility functions</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;lwres/lwres.h&gt;</funcsynopsisinfo>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_string_parse</function></funcdef>
<paramdef>lwres_buffer_t *b</paramdef>
<paramdef>char **c</paramdef>
<paramdef>lwres_uint16_t *len</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_addr_parse</function></funcdef>
<paramdef>lwres_buffer_t *b</paramdef>
<paramdef>lwres_addr_t *addr</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_getaddrsbyname</function></funcdef>
<paramdef>lwres_context_t *ctx</paramdef>
<paramdef>const char *name</paramdef>
<paramdef>lwres_uint32_t addrtypes</paramdef>
<paramdef>lwres_gabnresponse_t **structp</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_getnamebyaddr</function></funcdef>
<paramdef>lwres_context_t *ctx</paramdef>
<paramdef>lwres_uint32_t addrtype</paramdef>
<paramdef>lwres_uint16_t addrlen</paramdef>
<paramdef>const unsigned char *addr</paramdef>
<paramdef>lwres_gnbaresponse_t **structp</paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>

<refsect1>
<title>DESCRIPTION</title>

<para>
<function>lwres_string_parse()</function> retrieves a DNS-encoded
string starting the current pointer of lightweight resolver buffer
<parameter>b</parameter>: i.e.  <constant>b-&gt;current</constant>.
When the function returns, the address of the first byte of the
encoded string is returned via <parameter>*c</parameter> and the
length of that string is given by <parameter>*len</parameter>.  The
buffer's current pointer is advanced to point at the character
following the string length, the encoded string, and the trailing
<type>NULL</type> character.
</para>

<para>
<function>lwres_addr_parse()</function> extracts an address from the
buffer <parameter>b</parameter>.  The buffer's current pointer
<constant>b-&gt;current</constant> 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
<constant>addr-&gt;address</constant> and
<constant>addr-&gt;length</constant> indicates the size in bytes of
the address that was copied.  <constant>b-&gt;current</constant> is
advanced to point at the next byte of available data in the buffer
following the encoded address.
</para>

<para>
<function>lwres_getaddrsbyname()</function>
and
<function>lwres_getnamebyaddr()</function>
use the
<type>lwres_gnbaresponse_t</type>
structure defined below:
<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;
</programlisting>
The contents of this structure are not manipulated directly but
they are controlled through the
<citerefentry>
<refentrytitle>lwres_gabn</refentrytitle><manvolnum>3
</manvolnum>
</citerefentry>
functions.
</para>

<para>
The lightweight resolver uses
<function>lwres_getaddrsbyname()</function> to perform foward lookups.
Hostname <parameter>name</parameter> is looked up using the resolver
context <parameter>ctx</parameter> for memory allocation.
<parameter>addrtypes</parameter> is a bitmask indicating which type of
addresses are to be looked up.  Current values for this bitmask are
<type>LWRES_ADDRTYPE_V4</type> for IPv4 addresses and
<type>LWRES_ADDRTYPE_V6</type> for IPv6 addresses.  Results of the
lookup are returned in <parameter>*structp</parameter>.
</para>

<para>
<function>lwres_getnamebyaddr()</function> performs reverse lookups.
Resolver context <parameter>ctx</parameter> is used for memory
allocation.  The address type is indicated by
<parameter>addrtype</parameter>: <type>LWRES_ADDRTYPE_V4</type> or
<type>LWRES_ADDRTYPE_V6</type>.  The address to be looked up is given
by <parameter>addr</parameter> and its length is
<parameter>addrlen</parameter> bytes.  The result of the function call
is made available through <parameter>*structp</parameter>.
</para>
</refsect1>

<refsect1>
<title>RETURN VALUES</title>
<para>
Successful calls to
<function>lwres_string_parse()</function>
and
<function>lwres_addr_parse()</function>
return
<errorcode>LWRES_R_SUCCESS.</errorcode>
Both functions return
<errorcode>LWRES_R_FAILURE</errorcode>
if the buffer is corrupt or
<errorcode>LWRES_R_UNEXPECTEDEND</errorcode>
if the buffer has less space than expected for the components of the
encoded string or address.
</para>
<para>
<function>lwres_getaddrsbyname()</function>
returns
<errorcode>LWRES_R_SUCCESS</errorcode>
on success and it returns
<errorcode>LWRES_R_NOTFOUND</errorcode>
if the hostname
<parameter>name</parameter>
could not be found.
</para>
<para>
<errorcode>LWRES_R_SUCCESS</errorcode>
is returned by a successful call to
<function>lwres_getnamebyaddr()</function>.
</para>

<para>
Both
<function>lwres_getaddrsbyname()</function>
and
<function>lwres_getnamebyaddr()</function>
return
<errorcode>LWRES_R_NOMEMORY</errorcode>
when memory allocation requests fail and
<errorcode>LWRES_R_UNEXPECTEDEND</errorcode>
if the buffers used for sending queries and receiving replies are too
small.
</para>

</refsect1>
<refsect1>
<title>SEE ALSO</title>
<para>
<citerefentry>
<refentrytitle>lwres_buffer</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,

<citerefentry>
<refentrytitle>lwres_gabn</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>.
</para>

</refsect1>
</refentry>