lwres_resutil.docbook [plain text]
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<refentry>
<refentryinfo>
<date>Jun 30, 2000</date>
</refentryinfo>
<refmeta>
<refentrytitle>lwres_resutil</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>BIND9</refmiscinfo>
</refmeta>
<docinfo>
<copyright>
<year>2004</year>
<year>2005</year>
<year>2007</year>
<year>2012</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_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 <lwres/lwres.h></funcsynopsisinfo>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_string_parse</function></funcdef>
<paramdef>lwres_buffer_t *<parameter>b</parameter></paramdef>
<paramdef>char **<parameter>c</parameter></paramdef>
<paramdef>lwres_uint16_t *<parameter>len</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_addr_parse</function></funcdef>
<paramdef>lwres_buffer_t *<parameter>b</parameter></paramdef>
<paramdef>lwres_addr_t *<parameter>addr</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_getaddrsbyname</function></funcdef>
<paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
<paramdef>const char *<parameter>name</parameter></paramdef>
<paramdef>lwres_uint32_t <parameter>addrtypes</parameter></paramdef>
<paramdef>lwres_gabnresponse_t **<parameter>structp</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>
lwres_result_t
<function>lwres_getnamebyaddr</function></funcdef>
<paramdef>lwres_context_t *<parameter>ctx</parameter></paramdef>
<paramdef>lwres_uint32_t <parameter>addrtype</parameter></paramdef>
<paramdef>lwres_uint16_t <parameter>addrlen</parameter></paramdef>
<paramdef>const unsigned char *<parameter>addr</parameter></paramdef>
<paramdef>lwres_gnbaresponse_t **<parameter>structp</parameter></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->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->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->address</constant> and
<constant>addr->length</constant> indicates the size in bytes
of the address that was copied.
<constant>b->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:
</para>
<para><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></para>
<para>
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>
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