<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN"><!-- - Copyright (C) 2004  Internet Systems Consortium, Inc. ("ISC") - Copyright (C) 2001  Internet Software Consortium. - - Permission to use, copy, modify, and distribute this software for any - purpose with or without fee is hereby granted, provided that the above - copyright notice and this permission notice appear in all copies. - - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY - AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE - OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR - PERFORMANCE OF THIS SOFTWARE.--><!-- $Id: lwres_gethostent.docbook,v 1.2 2004/09/20 18:00:50 mcr Exp $ --><refentry><refentryinfo><date>Jun 30, 2000</date></refentryinfo><refmeta><refentrytitle>lwres_gethostent</refentrytitle><manvolnum>3</manvolnum><refmiscinfo>BIND9</refmiscinfo></refmeta><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 *name</paramdef></funcprototype><funcprototype><funcdef>struct hostent *<function>lwres_gethostbyname2</function></funcdef><paramdef>const char *name</paramdef><paramdef>int af</paramdef></funcprototype><funcprototype><funcdef>struct hostent *<function>lwres_gethostbyaddr</function></funcdef><paramdef>const char *addr</paramdef><paramdef>int len</paramdef><paramdef>int type</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 stayopen</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 *name</paramdef><paramdef>struct hostent *resbuf</paramdef><paramdef>char *buf</paramdef><paramdef>int buflen</paramdef><paramdef>int *error</paramdef></funcprototype><funcprototype><funcdef>struct hostent  *<function>lwres_gethostbyaddr_r</function></funcdef><paramdef>const char *addr</paramdef><paramdef>int len</paramdef><paramdef>int type</paramdef><paramdef>struct hostent *resbuf</paramdef><paramdef>char *buf</paramdef><paramdef>int buflen</paramdef><paramdef>int *error</paramdef></funcprototype><funcprototype><funcdef>struct hostent  *<function>lwres_gethostent_r</function></funcdef><paramdef>struct hostent *resbuf</paramdef><paramdef>char *buf</paramdef><paramdef>int buflen</paramdef><paramdef>int *error</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_sethostent_r</function></funcdef><paramdef>int stayopen</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_endhostent_r</function></funcdef><paramdef>void</paramdef></funcprototype></funcsynopsis></refsynopsisdiv><refsect1><title>DESCRIPTION</title><para>These functions provide hostname-to-address andaddress-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>.<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 thatprovide such functionality through facilities like<filename>/etc/hosts</filename>or NIS.  The lightweight resolver does not currently implementthese functions; it only provides them as stub functions that alwaysreturn 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 IPv4address while <function>lwres_gethostbyname2()</function> looks for anaddress of protocol family <parameter>af</parameter>: either<type>PF_INET</type> or <type>PF_INET6</type> &mdash; IPv4 or IPV6addresses 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 functionfor forward lookups.  If an error occurs, an error code is returned in<parameter>*error</parameter>.<parameter>resbuf</parameter> is a pointer to a <type>structhostent</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>structhostent</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 functionthat performs a reverse lookup of address <parameter>addr</parameter>which is <parameter>len</parameter> bytes long and is of protocolfamily <parameter>type</parameter> &mdash; <type>PF_INET</type> or<type>PF_INET6</type>.  If an error occurs, the error code is returnedin <parameter>*error</parameter>.  The other function parameters areidentical to those in <function>lwres_gethostbyname_r()</function>.<parameter>resbuf</parameter> is a pointer to a <type>structhostent</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>structhostent</type> returned in <parameter>resbuf</parameter>.  Successfulcalls to <function>lwres_gethostbyaddr_r()</function> return<parameter>resbuf</parameter>, which is a pointer to the<function>struct hostent()</function> it created.</para></refsect1><refsect1><title>RETURN VALUES</title><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 informationassociated with it (or vice versa in the caseof a reverse lookup).  The code NO_ADDRESSis accepted as a synonym for NO_DATA for backwardscompatibility.</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>structhostent</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 bythe <constant>h_name</constant>, <constant>h_aliases</constant>, and<constant>h_addr_list</constant> elements of the <type>structhostent</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></refsect1><refsect1><title>SEE ALSO</title><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></refsect1><refsect1><title>BUGS</title><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-DNSname services such as <filename>/etc/hosts</filename>or<type>NIS</type>,consequently the above functions don't, either.</para></refsect1></refentry>