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<refentry xmlns="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>