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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
<a name="id2476275"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>lwres_getipnodebyname, lwres_getipnodebyaddr, lwres_freehostent — lightweight resolver nodename / address translation API</p>
</div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="funcsynopsis">
<pre class="funcsynopsisinfo">#include <lwres/netdb.h></pre>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
struct hostent *
<b class="fsfunc">lwres_getipnodebyname</b>(</code></td>
<td>const char * </td>
<td>
<var class="pdparam">name</var>, </td>
</tr>
<tr>
<td> </td>
<td>int </td>
<td>
<var class="pdparam">af</var>, </td>
</tr>
<tr>
<td> </td>
<td>int </td>
<td>
<var class="pdparam">flags</var>, </td>
</tr>
<tr>
<td> </td>
<td>int * </td>
<td>
<var class="pdparam">error_num</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
struct hostent *
<b class="fsfunc">lwres_getipnodebyaddr</b>(</code></td>
<td>const void * </td>
<td>
<var class="pdparam">src</var>, </td>
</tr>
<tr>
<td> </td>
<td>size_t </td>
<td>
<var class="pdparam">len</var>, </td>
</tr>
<tr>
<td> </td>
<td>int </td>
<td>
<var class="pdparam">af</var>, </td>
</tr>
<tr>
<td> </td>
<td>int * </td>
<td>
<var class="pdparam">error_num</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_freehostent</b>(</code></td>
<td>struct hostent * </td>
<td>
<var class="pdparam">he</var><code>)</code>;</td>
</tr></table>
</div>
</div>
<div class="refsect1" lang="en">
<a name="id2543435"></a><h2>DESCRIPTION</h2>
<p>
These functions perform thread safe, protocol independent
nodename-to-address and address-to-nodename
translation as defined in RFC2553.
</p>
<p>
They use a
<span class="type">struct hostent</span>
which is defined in
<code class="filename">namedb.h</code>:
</p>
<pre class="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 */
</pre>
<p>
</p>
<p>
The members of this structure are:
</p>
<div class="variablelist"><dl>
<dt><span class="term"><code class="constant">h_name</code></span></dt>
<dd><p>
The official (canonical) name of the host.
</p></dd>
<dt><span class="term"><code class="constant">h_aliases</code></span></dt>
<dd><p>
A NULL-terminated array of alternate names (nicknames) for the
host.
</p></dd>
<dt><span class="term"><code class="constant">h_addrtype</code></span></dt>
<dd><p>
The type of address being returned - usually
<span class="type">PF_INET</span>
or
<span class="type">PF_INET6</span>.
</p></dd>
<dt><span class="term"><code class="constant">h_length</code></span></dt>
<dd><p>
The length of the address in bytes.
</p></dd>
<dt><span class="term"><code class="constant">h_addr_list</code></span></dt>
<dd><p>
A
<span class="type">NULL</span>
terminated array of network addresses for the host.
Host addresses are returned in network byte order.
</p></dd>
</dl></div>
<p>
</p>
<p><code class="function">lwres_getipnodebyname()</code>
looks up addresses of protocol family <em class="parameter"><code>af</code></em>
for the hostname <em class="parameter"><code>name</code></em>. The
<em class="parameter"><code>flags</code></em> 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:
</p>
<div class="variablelist"><dl>
<dt><span class="term"><code class="constant">AI_V4MAPPED</code></span></dt>
<dd><p>
This is used with an
<em class="parameter"><code>af</code></em>
of AF_INET6, and causes IPv4 addresses to be returned as
IPv4-mapped
IPv6 addresses.
</p></dd>
<dt><span class="term"><code class="constant">AI_ALL</code></span></dt>
<dd><p>
This is used with an
<em class="parameter"><code>af</code></em>
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.
</p></dd>
<dt><span class="term"><code class="constant">AI_ADDRCONFIG</code></span></dt>
<dd><p>
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.
</p></dd>
<dt><span class="term"><code class="constant">AI_DEFAULT</code></span></dt>
<dd><p>
This default sets the
<code class="constant">AI_V4MAPPED</code>
and
<code class="constant">AI_ADDRCONFIG</code>
flag bits.
</p></dd>
</dl></div>
<p>
</p>
<p><code class="function">lwres_getipnodebyaddr()</code>
performs a reverse lookup of address <em class="parameter"><code>src</code></em>
which is <em class="parameter"><code>len</code></em> bytes long.
<em class="parameter"><code>af</code></em> denotes the protocol family, typically
<span class="type">PF_INET</span> or <span class="type">PF_INET6</span>.
</p>
<p><code class="function">lwres_freehostent()</code>
releases all the memory associated with the <span class="type">struct
hostent</span> pointer <em class="parameter"><code>he</code></em>. Any memory
allocated for the <code class="constant">h_name</code>,
<code class="constant">h_addr_list</code> and
<code class="constant">h_aliases</code> is freed, as is the memory for
the <span class="type">hostent</span> structure itself.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2543693"></a><h2>RETURN VALUES</h2>
<p>
If an error occurs,
<code class="function">lwres_getipnodebyname()</code>
and
<code class="function">lwres_getipnodebyaddr()</code>
set
<em class="parameter"><code>*error_num</code></em>
to an appropriate error code and the function returns a
<span class="type">NULL</span>
pointer.
The error codes and their meanings are defined in
<code class="filename"><lwres/netdb.h></code>:
</p>
<div class="variablelist"><dl>
<dt><span class="term"><code class="constant">HOST_NOT_FOUND</code></span></dt>
<dd><p>
No such host is known.
</p></dd>
<dt><span class="term"><code class="constant">NO_ADDRESS</code></span></dt>
<dd><p>
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.
</p></dd>
<dt><span class="term"><code class="constant">TRY_AGAIN</code></span></dt>
<dd><p>
A temporary and possibly transient error occurred, such as a
failure of a server to respond. The request may succeed if
retried.
</p></dd>
<dt><span class="term"><code class="constant">NO_RECOVERY</code></span></dt>
<dd><p>
An unexpected failure occurred, and retrying the request
is pointless.
</p></dd>
</dl></div>
<p>
</p>
<p><span class="citerefentry"><span class="refentrytitle">lwres_hstrerror</span>(3)</span>
translates these error codes to suitable error messages.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2543790"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry"><span class="refentrytitle">RFC2553</span></span>,
<span class="citerefentry"><span class="refentrytitle">lwres</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_gethostent</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_getaddrinfo</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_getnameinfo</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_hstrerror</span>(3)</span>.
</p>
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