]>

 - Copyright (C) Internet Systems Consortium, Inc. ("ISC")

 -

 - This Source Code Form is subject to the terms of the Mozilla Public

 - License, v. 2.0. If a copy of the MPL was not distributed with this

 - file, You can obtain one at http://mozilla.org/MPL/2.0/.

 -

 - See the COPYRIGHT file distributed with this work for additional

 - information regarding copyright ownership.

-->

<refentry xmlns:db="http://docbook.org/ns/docbook" version="5.0">

  <info>

    <date>2007-06-18</date>

  </info>

  <refentryinfo>

    <corpname>ISC</corpname>

    <corpauthor>Internet Systems Consortium, Inc.</corpauthor>

  </refentryinfo>

  <refmeta>

    <refentrytitle>lwres_gethostent</refentrytitle>

    <manvolnum>3</manvolnum>

    <refmiscinfo>BIND9</refmiscinfo>

  </refmeta>

  <docinfo>

    <copyright>

      <year>2001</year>

      <year>2004</year>

      <year>2005</year>

      <year>2007</year>

      <year>2014</year>

      <year>2015</year>

      <year>2016</year>

      <year>2018</year>

      <year>2019</year>

      <year>2020</year>

      <holder>Internet Systems Consortium, Inc. ("ISC")</holder>

    </copyright>

  </docinfo>

  <refnamediv>

    <refname>lwres_gethostbyname</refname>

    <refname>lwres_gethostbyname2</refname>

    <refname>lwres_gethostbyaddr</refname>

    <refname>lwres_gethostent</refname>

    <refname>lwres_sethostent</refname>

    <refname>lwres_endhostent</refname>

    <refname>lwres_gethostbyname_r</refname>

    <refname>lwres_gethostbyaddr_r</refname>

    <refname>lwres_gethostent_r</refname>

    <refname>lwres_sethostent_r</refname>

    <refname>lwres_endhostent_r</refname>

    <refpurpose>lightweight resolver get network host entry</refpurpose>

  </refnamediv>

  <refsynopsisdiv>

    <funcsynopsis>

<funcsynopsisinfo>#include <lwres/netdb.h></funcsynopsisinfo>

<funcprototype>

        <funcdef>

struct hostent *

<function>lwres_gethostbyname</function></funcdef>

        <paramdef>const char *<parameter>name</parameter></paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

struct hostent *

<function>lwres_gethostbyname2</function></funcdef>

        <paramdef>const char *<parameter>name</parameter></paramdef>

        <paramdef>int <parameter>af</parameter></paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

struct hostent *

<function>lwres_gethostbyaddr</function></funcdef>

        <paramdef>const char *<parameter>addr</parameter></paramdef>

        <paramdef>int <parameter>len</parameter></paramdef>

        <paramdef>int <parameter>type</parameter></paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

struct hostent *

<function>lwres_gethostent</function></funcdef>

        <paramdef>void</paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

void

<function>lwres_sethostent</function></funcdef>

        <paramdef>int <parameter>stayopen</parameter></paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

void

<function>lwres_endhostent</function></funcdef>

        <paramdef>void</paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

struct hostent *

<function>lwres_gethostbyname_r</function></funcdef>

        <paramdef>const char *<parameter>name</parameter></paramdef>

        <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>

        <paramdef>char *<parameter>buf</parameter></paramdef>

        <paramdef>int <parameter>buflen</parameter></paramdef>

        <paramdef>int *<parameter>error</parameter></paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

struct hostent  *

<function>lwres_gethostbyaddr_r</function></funcdef>

        <paramdef>const char *<parameter>addr</parameter></paramdef>

        <paramdef>int <parameter>len</parameter></paramdef>

        <paramdef>int <parameter>type</parameter></paramdef>

        <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>

        <paramdef>char *<parameter>buf</parameter></paramdef>

        <paramdef>int <parameter>buflen</parameter></paramdef>

        <paramdef>int *<parameter>error</parameter></paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

struct hostent  *

<function>lwres_gethostent_r</function></funcdef>

        <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>

        <paramdef>char *<parameter>buf</parameter></paramdef>

        <paramdef>int <parameter>buflen</parameter></paramdef>

        <paramdef>int *<parameter>error</parameter></paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

void

<function>lwres_sethostent_r</function></funcdef>

        <paramdef>int <parameter>stayopen</parameter></paramdef>

        </funcprototype>

<funcprototype>

        <funcdef>

void

<function>lwres_endhostent_r</function></funcdef>

        <paramdef>void</paramdef>

      </funcprototype>

</funcsynopsis>

  </refsynopsisdiv>

  <refsection><info><title>DESCRIPTION</title></info>

    <para>

      These functions provide hostname-to-address and

      address-to-hostname lookups by means of the lightweight resolver.

      They are similar to the standard

      <citerefentry>

        <refentrytitle>gethostent</refentrytitle><manvolnum>3</manvolnum>

      </citerefentry>

      functions provided by most operating systems.

      They use a

      <type>struct hostent</type>

      which is usually defined in

      <filename><namedb.h></filename>.

    </para>

    <para><programlisting>

struct  hostent {

        char    *h_name;        /* official name of host */

        char    **h_aliases;    /* alias list */

        int     h_addrtype;     /* host address type */

        int     h_length;       /* length of address */

        char    **h_addr_list;  /* list of addresses from name server */

};

#define h_addr  h_addr_list[0]  /* address, for backward compatibility */

</programlisting>

    </para>

    <para>

      The members of this structure are:

      <variablelist>

        <varlistentry>

          <term><constant>h_name</constant></term>

          <listitem>

            <para>

              The official (canonical) name of the host.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><constant>h_aliases</constant></term>

          <listitem>

            <para>

              A NULL-terminated array of alternate names (nicknames) for the

              host.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><constant>h_addrtype</constant></term>

          <listitem>

            <para>

              The type of address being returned —

              <type>PF_INET</type>

              or

              <type>PF_INET6</type>.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><constant>h_length</constant></term>

          <listitem>

            <para>

              The length of the address in bytes.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><constant>h_addr_list</constant></term>

          <listitem>

            <para>

              A <type>NULL</type>

              terminated array of network addresses for the host.

              Host addresses are returned in network byte order.

            </para>

          </listitem>

        </varlistentry>

      </variablelist>

    </para>

    <para>

      For backward compatibility with very old software,

      <constant>h_addr</constant>

      is the first address in

      <constant>h_addr_list.</constant>

    </para>

    <para><function>lwres_gethostent()</function>,

      <function>lwres_sethostent()</function>,

      <function>lwres_endhostent()</function>,

      <function>lwres_gethostent_r()</function>,

      <function>lwres_sethostent_r()</function>

      and

      <function>lwres_endhostent_r()</function>

      provide iteration over the known host entries on systems that

      provide such functionality through facilities like

      <filename>/etc/hosts</filename>

      or NIS.  The lightweight resolver does not currently implement

      these functions; it only provides them as stub functions that always

      return failure.

    </para>

    <para><function>lwres_gethostbyname()</function>

      and <function>lwres_gethostbyname2()</function> look up the

      hostname <parameter>name</parameter>.

      <function>lwres_gethostbyname()</function> always looks for an

      IPv4 address while <function>lwres_gethostbyname2()</function>

      looks for an address of protocol family

      <parameter>af</parameter>: either <type>PF_INET</type> or

      <type>PF_INET6</type> — IPv4 or IPV6 addresses

      respectively.  Successful calls of the functions return a

      <type>struct hostent</type>for the name that was looked up.

      <type>NULL</type> is returned if the lookups by

      <function>lwres_gethostbyname()</function> or

      <function>lwres_gethostbyname2()</function> fail.

    </para>

    <para>

      Reverse lookups of addresses are performed by

      <function>lwres_gethostbyaddr()</function>.

      <parameter>addr</parameter> is an address of length

      <parameter>len</parameter> bytes and protocol family

      <parameter>type</parameter> — <type>PF_INET</type> or

      <type>PF_INET6</type>.

      <function>lwres_gethostbyname_r()</function> is a

      thread-safe function

      for forward lookups.  If an error occurs, an error code is returned in

      <parameter>*error</parameter>.

      <parameter>resbuf</parameter> is a pointer to a

      <type>struct hostent</type> which is initialised by a successful call to

      <function>lwres_gethostbyname_r()</function>.

      <parameter>buf</parameter> is a buffer of length

      <parameter>len</parameter> bytes which is used to store the

      <constant>h_name</constant>, <constant>h_aliases</constant>, and

      <constant>h_addr_list</constant> elements of the

      <type>struct hostent</type> returned in <parameter>resbuf</parameter>.

      Successful calls to <function>lwres_gethostbyname_r()</function>

      return <parameter>resbuf</parameter>,

      which is a pointer to the <type>struct hostent</type> it created.

    </para>

    <para><function>lwres_gethostbyaddr_r()</function>

      is a thread-safe function

      that performs a reverse lookup of address <parameter>addr</parameter>

      which is <parameter>len</parameter> bytes long and is of

      protocol

      family <parameter>type</parameter> — <type>PF_INET</type> or

      <type>PF_INET6</type>.  If an error occurs, the error code is returned

      in <parameter>*error</parameter>.  The other function

      parameters are

      identical to those in <function>lwres_gethostbyname_r()</function>.

      <parameter>resbuf</parameter> is a pointer to a

      <type>struct hostent</type> which is initialised by a successful call to

      <function>lwres_gethostbyaddr_r()</function>.

      <parameter>buf</parameter> is a buffer of length

      <parameter>len</parameter> bytes which is used to store the

      <constant>h_name</constant>, <constant>h_aliases</constant>, and

      <constant>h_addr_list</constant> elements of the

      <type>struct hostent</type> returned in <parameter>resbuf</parameter>.

      Successful calls to <function>lwres_gethostbyaddr_r()</function> return

      <parameter>resbuf</parameter>, which is a pointer to the

      <function>struct hostent()</function> it created.

    </para>

  </refsection>

  <refsection><info><title>RETURN VALUES</title></info>

    <para>

      The functions

      <function>lwres_gethostbyname()</function>,

      <function>lwres_gethostbyname2()</function>,

      <function>lwres_gethostbyaddr()</function>,

      and

      <function>lwres_gethostent()</function>

      return NULL to indicate an error.  In this case the global variable

      <type>lwres_h_errno</type>

      will contain one of the following error codes defined in

      <filename><lwres/netdb.h></filename>:

      <variablelist>

        <varlistentry>

          <term><constant>HOST_NOT_FOUND</constant></term>

          <listitem>

            <para>

              The host or address was not found.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><constant>TRY_AGAIN</constant></term>

          <listitem>

            <para>

              A recoverable error occurred, e.g., a timeout.

              Retrying the lookup may succeed.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><constant>NO_RECOVERY</constant></term>

          <listitem>

            <para>

              A non-recoverable error occurred.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><constant>NO_DATA</constant></term>

          <listitem>

            <para>

              The name exists, but has no address information

              associated with it (or vice versa in the case

              of a reverse lookup).  The code NO_ADDRESS

              is accepted as a synonym for NO_DATA for backwards

              compatibility.

            </para>

          </listitem>

        </varlistentry>

      </variablelist>

    </para>

    <para><citerefentry>

        <refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>

      </citerefentry>

      translates these error codes to suitable error messages.

    </para>

    <para><function>lwres_gethostent()</function>

      and <function>lwres_gethostent_r()</function>

      always return <type>NULL</type>.

    </para>

    <para>

      Successful calls to <function>lwres_gethostbyname_r()</function> and

      <function>lwres_gethostbyaddr_r()</function> return

      <parameter>resbuf</parameter>, a pointer to the

      <type>struct hostent</type> that was initialised by these functions.  They return

      <type>NULL</type> if the lookups fail or if <parameter>buf</parameter>

      was too small to hold the list of addresses and names referenced by

      the <constant>h_name</constant>, <constant>h_aliases</constant>, and

      <constant>h_addr_list</constant> elements of the

      <type>struct hostent</type>.

      If <parameter>buf</parameter> was too small, both

      <function>lwres_gethostbyname_r()</function> and

      <function>lwres_gethostbyaddr_r()</function> set the global

      variable

      <type>errno</type> to <errorcode>ERANGE</errorcode>.

    </para>

  </refsection>

  <refsection><info><title>SEE ALSO</title></info>

    <para><citerefentry>

        <refentrytitle>gethostent</refentrytitle><manvolnum>3</manvolnum>

      </citerefentry>,

      <citerefentry>

        <refentrytitle>lwres_getipnode</refentrytitle><manvolnum>3</manvolnum>

      </citerefentry>,

      <citerefentry>

        <refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>

      </citerefentry>

    </para>

  </refsection>

  <refsection><info><title>BUGS</title></info>

    <para><function>lwres_gethostbyname()</function>,

      <function>lwres_gethostbyname2()</function>,

      <function>lwres_gethostbyaddr()</function>

      and

      <function>lwres_endhostent()</function>

      are not thread safe; they return pointers to static data and

      provide error codes through a global variable.

      Thread-safe versions for name and address lookup are provided by

      <function>lwres_gethostbyname_r()</function>,

      and

      <function>lwres_gethostbyaddr_r()</function>

      respectively.

    </para>

    <para>

      The resolver daemon does not currently support any non-DNS

      name services such as

      <filename>/etc/hosts</filename>

      or

      <type>NIS</type>,

      consequently the above functions don't, either.

    </para>

  </refsection>

</refentry>