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<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>2004</year>
      <year>2005</year>
      <year>2007</year>
      <year>2014</year>
      <year>2015</year>
      <year>2016</year>
      <holder>Internet Systems Consortium, Inc. ("ISC")</holder>
    </copyright>
    <copyright>
      <year>2001</year>
      <holder>Internet Software Consortium.</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 &lt;lwres/netdb.h&gt;</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>&lt;namedb.h&gt;</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 &mdash;
              <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> &mdash; 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> &mdash; <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> &mdash; <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>&lt;lwres/netdb.h&gt;</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>
