lwres_getipnode.docbook

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<refentry>

<refentryinfo>
<date>Jun 30, 2000</date>
</refentryinfo>

<refmeta>
<refentrytitle>lwres_getipnode</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>BIND9</refmiscinfo>
</refmeta>

<refnamediv>
<refname>lwres_getipnodebyname</refname>
<refname>lwres_getipnodebyaddr</refname>
<refname>lwres_freehostent</refname>
<refpurpose>lightweight resolver nodename / address translation API</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;lwres/netdb.h&gt;</funcsynopsisinfo>
<funcprototype>
<funcdef>
struct hostent *
<function>lwres_getipnodebyname</function></funcdef>
<paramdef>const char *name</paramdef>
<paramdef>int af</paramdef>
<paramdef>int flags</paramdef>
<paramdef>int *error_num</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
struct hostent *
<function>lwres_getipnodebyaddr</function></funcdef>
<paramdef>const void *src</paramdef>
<paramdef>size_t len</paramdef>
<paramdef>int af</paramdef>
<paramdef>int *error_num</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
void
<function>lwres_freehostent</function></funcdef>
<paramdef>struct hostent *he</paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>

<refsect1>
<title>DESCRIPTION</title>

<para>
These functions perform thread safe, protocol independent
nodename-to-address and address-to-nodename 
translation as defined in RFC2553.
</para>

<para>
They use a
<type>struct hostent</type>
which is defined in
<filename>namedb.h</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 - usually
<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>
<function>lwres_getipnodebyname()</function>
looks up addresses of protocol family
<parameter>af</parameter>

for the hostname
<parameter>name</parameter>.

The
<parameter>flags</parameter>
parameter contains ORed flag bits to 
specify the types of addresses that are searched
for, and the types of addresses that are returned. 
The flag bits are:
<variablelist>
<varlistentry><term><constant>AI_V4MAPPED</constant></term>
<listitem>
<para>
This is used with an
<parameter>af</parameter>
of AF_INET6, and causes IPv4 addresses to be returned as IPv4-mapped
IPv6 addresses.
</para>
</listitem></varlistentry>
<varlistentry><term><constant>AI_ALL</constant></term>
<listitem>
<para>
This is used with an
<parameter>af</parameter>
of AF_INET6, and causes all known addresses (IPv6 and IPv4) to be returned.
If AI_V4MAPPED is also set, the IPv4 addresses are return as mapped
IPv6 addresses.
</para>
</listitem></varlistentry>
<varlistentry><term><constant>AI_ADDRCONFIG</constant></term>
<listitem>
<para>
Only return an IPv6 or IPv4 address if here is an active network
interface of that type.  This is not currently implemented
in the BIND 9 lightweight resolver, and the flag is ignored.
</para>
</listitem></varlistentry>
<varlistentry><term><constant>AI_DEFAULT</constant></term>
<listitem>
<para>
This default sets the
<constant>AI_V4MAPPED</constant>
and
<constant>AI_ADDRCONFIG</constant>
flag bits.
</para>
</listitem></varlistentry>
</variablelist>
</para>
<para>
<function>lwres_getipnodebyaddr()</function>
performs a reverse lookup
of address
<parameter>src</parameter>
which is
<parameter>len</parameter>
bytes long.
<parameter>af</parameter>
denotes the protocol family, typically
<type>PF_INET</type>
or
<type>PF_INET6</type>.

</para>
<para>
<function>lwres_freehostent()</function>
releases all the memory associated with
the
<type>struct hostent</type>
pointer
<parameter>he</parameter>.

Any memory allocated for the
<constant>h_name</constant>,

<constant>h_addr_list</constant>
and
<constant>h_aliases</constant>
is freed, as is the memory for the
<type>hostent</type>
structure itself.
</para>
</refsect1>
<refsect1>
<title>RETURN VALUES</title>
<para>
If an error occurs,
<function>lwres_getipnodebyname()</function>
and
<function>lwres_getipnodebyaddr()</function>
set
<parameter>*error_num</parameter>
to an appropriate error code and the function returns a
<type>NULL</type>
pointer.
The error codes and their meanings are defined in
<filename>&lt;lwres/netdb.h&gt;</filename>:
<variablelist>
<varlistentry><term><constant>HOST_NOT_FOUND</constant></term>
<listitem>
<para>
No such host is known.
</para>
</listitem></varlistentry>
<varlistentry><term><constant>NO_ADDRESS</constant></term>
<listitem>
<para>
The server recognised the request and the name but no address is
available.  Another type of request to the name server for the
domain might return an answer.
</para>
</listitem></varlistentry>
<varlistentry><term><constant>TRY_AGAIN</constant></term>
<listitem>
<para>
A temporary and possibly transient error occurred, such as a
failure of a server to respond.  The request may succeed if
retried.
</para>
</listitem></varlistentry>
<varlistentry><term><constant>NO_RECOVERY</constant></term>
<listitem>
<para>
An unexpected failure occurred, and retrying the request
is pointless.
</para>
</listitem></varlistentry>
</variablelist>
</para>
<para>
<citerefentry>
<refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3
</manvolnum>
</citerefentry>
translates these error codes to suitable error messages.
</para>
</refsect1>
<refsect1>
<title>SEE ALSO</title>
<para>
<citerefentry>
<refentrytitle>RFC2553</refentrytitle>
</citerefentry>,

<citerefentry>
<refentrytitle>lwres</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,

<citerefentry>
<refentrytitle>lwres_gethostent</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,

<citerefentry>
<refentrytitle>lwres_getaddrinfo</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,

<citerefentry>
<refentrytitle>lwres_getnameinfo</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,

<citerefentry>
<refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>.
</para>
</refsect1>
</refentry>