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phunix/external/bsd/bind/dist/lib/lwres/man/lwres_gethostent.html
David van Moolenbroek 00b67f09dd Import NetBSD named(8) 
Also known as ISC bind.  This import adds utilities such as host(1),
dig(1), and nslookup(1), as well as many other tools and libraries.

Change-Id: I035ca46e64f1965d57019e773f4ff0ef035e4aa3
2017-03-21 22:00:06 +00:00

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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>lwres_gethostent</title>
<meta name="generator" content="DocBook XSL Stylesheets V1.71.1">
</head>
<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_gethostbyname, lwres_gethostbyname2, lwres_gethostbyaddr, lwres_gethostent, lwres_sethostent, lwres_endhostent, lwres_gethostbyname_r, lwres_gethostbyaddr_r, lwres_gethostent_r, lwres_sethostent_r, lwres_endhostent_r &#8212; lightweight resolver get network host entry</p>
</div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="funcsynopsis">
<pre class="funcsynopsisinfo">#include &lt;lwres/netdb.h&gt;</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_gethostbyname</b>(</code></td>
<td>const char * </td>
<td>
<var class="pdparam">name</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_gethostbyname2</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><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_gethostbyaddr</b>(</code></td>
<td>const char * </td>
<td>
<var class="pdparam">addr</var>, </td>
</tr>
<tr>
<td> </td>
<td>int  </td>
<td>
<var class="pdparam">len</var>, </td>
</tr>
<tr>
<td> </td>
<td>int  </td>
<td>
<var class="pdparam">type</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_gethostent</b>(</code></td>
<td> </td>
<td>
<code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_sethostent</b>(</code></td>
<td>int  </td>
<td>
<var class="pdparam">stayopen</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">
void
<b class="fsfunc">lwres_endhostent</b>(</code></td>
<td> </td>
<td>
<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_gethostbyname_r</b>(</code></td>
<td>const char * </td>
<td>
<var class="pdparam">name</var>, </td>
</tr>
<tr>
<td> </td>
<td>struct hostent * </td>
<td>
<var class="pdparam">resbuf</var>, </td>
</tr>
<tr>
<td> </td>
<td>char * </td>
<td>
<var class="pdparam">buf</var>, </td>
</tr>
<tr>
<td> </td>
<td>int  </td>
<td>
<var class="pdparam">buflen</var>, </td>
</tr>
<tr>
<td> </td>
<td>int * </td>
<td>
<var class="pdparam">error</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_gethostbyaddr_r</b>(</code></td>
<td>const char * </td>
<td>
<var class="pdparam">addr</var>, </td>
</tr>
<tr>
<td> </td>
<td>int  </td>
<td>
<var class="pdparam">len</var>, </td>
</tr>
<tr>
<td> </td>
<td>int  </td>
<td>
<var class="pdparam">type</var>, </td>
</tr>
<tr>
<td> </td>
<td>struct hostent * </td>
<td>
<var class="pdparam">resbuf</var>, </td>
</tr>
<tr>
<td> </td>
<td>char * </td>
<td>
<var class="pdparam">buf</var>, </td>
</tr>
<tr>
<td> </td>
<td>int  </td>
<td>
<var class="pdparam">buflen</var>, </td>
</tr>
<tr>
<td> </td>
<td>int * </td>
<td>
<var class="pdparam">error</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_gethostent_r</b>(</code></td>
<td>struct hostent * </td>
<td>
<var class="pdparam">resbuf</var>, </td>
</tr>
<tr>
<td> </td>
<td>char * </td>
<td>
<var class="pdparam">buf</var>, </td>
</tr>
<tr>
<td> </td>
<td>int  </td>
<td>
<var class="pdparam">buflen</var>, </td>
</tr>
<tr>
<td> </td>
<td>int * </td>
<td>
<var class="pdparam">error</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">
void
<b class="fsfunc">lwres_sethostent_r</b>(</code></td>
<td>int  </td>
<td>
<var class="pdparam">stayopen</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_endhostent_r</b>(</code></td>
<td> </td>
<td>
<code>)</code>;</td>
</tr></table>
</div>
</div>
<div class="refsect1" lang="en">
<a name="id2543618"></a><h2>DESCRIPTION</h2>
<p>
These functions provide hostname-to-address and
address-to-hostname lookups by means of the lightweight resolver.
They are similar to the standard
<span class="citerefentry"><span class="refentrytitle">gethostent</span>(3)</span>
functions provided by most operating systems.
They use a
<span class="type">struct hostent</span>
which is usually defined in
<code class="filename">&lt;namedb.h&gt;</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 &#8212;
<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>
For backward compatibility with very old software,
<code class="constant">h_addr</code>
is the first address in
<code class="constant">h_addr_list.</code>
</p>
<p><code class="function">lwres_gethostent()</code>,
<code class="function">lwres_sethostent()</code>,
<code class="function">lwres_endhostent()</code>,
<code class="function">lwres_gethostent_r()</code>,
<code class="function">lwres_sethostent_r()</code>
and
<code class="function">lwres_endhostent_r()</code>
provide iteration over the known host entries on systems that
provide such functionality through facilities like
<code class="filename">/etc/hosts</code>
or NIS. The lightweight resolver does not currently implement
these functions; it only provides them as stub functions that always
return failure.
</p>
<p><code class="function">lwres_gethostbyname()</code>
and <code class="function">lwres_gethostbyname2()</code> look up the
hostname <em class="parameter"><code>name</code></em>.
<code class="function">lwres_gethostbyname()</code> always looks for an
IPv4 address while <code class="function">lwres_gethostbyname2()</code>
looks for an address of protocol family
<em class="parameter"><code>af</code></em>: either <span class="type">PF_INET</span> or
<span class="type">PF_INET6</span> &#8212; IPv4 or IPV6 addresses
respectively. Successful calls of the functions return a
<span class="type">struct hostent</span>for the name that was looked up.
<span class="type">NULL</span> is returned if the lookups by
<code class="function">lwres_gethostbyname()</code> or
<code class="function">lwres_gethostbyname2()</code> fail.
</p>
<p>
Reverse lookups of addresses are performed by
<code class="function">lwres_gethostbyaddr()</code>.
<em class="parameter"><code>addr</code></em> is an address of length
<em class="parameter"><code>len</code></em> bytes and protocol family
<em class="parameter"><code>type</code></em> &#8212; <span class="type">PF_INET</span> or
<span class="type">PF_INET6</span>.
<code class="function">lwres_gethostbyname_r()</code> is a
thread-safe function
for forward lookups. If an error occurs, an error code is returned in
<em class="parameter"><code>*error</code></em>.
<em class="parameter"><code>resbuf</code></em> is a pointer to a
<span class="type">struct hostent</span> which is initialised by a successful call to
<code class="function">lwres_gethostbyname_r()</code>.
<em class="parameter"><code>buf</code></em> is a buffer of length
<em class="parameter"><code>len</code></em> bytes which is used to store the
<code class="constant">h_name</code>, <code class="constant">h_aliases</code>, and
<code class="constant">h_addr_list</code> elements of the
<span class="type">struct hostent</span> returned in <em class="parameter"><code>resbuf</code></em>.
Successful calls to <code class="function">lwres_gethostbyname_r()</code>
return <em class="parameter"><code>resbuf</code></em>,
which is a pointer to the <span class="type">struct hostent</span> it created.
</p>
<p><code class="function">lwres_gethostbyaddr_r()</code>
is a thread-safe function
that performs a reverse lookup of address <em class="parameter"><code>addr</code></em>
which is <em class="parameter"><code>len</code></em> bytes long and is of
protocol
family <em class="parameter"><code>type</code></em> &#8212; <span class="type">PF_INET</span> or
<span class="type">PF_INET6</span>. If an error occurs, the error code is returned
in <em class="parameter"><code>*error</code></em>. The other function
parameters are
identical to those in <code class="function">lwres_gethostbyname_r()</code>.
<em class="parameter"><code>resbuf</code></em> is a pointer to a
<span class="type">struct hostent</span> which is initialised by a successful call to
<code class="function">lwres_gethostbyaddr_r()</code>.
<em class="parameter"><code>buf</code></em> is a buffer of length
<em class="parameter"><code>len</code></em> bytes which is used to store the
<code class="constant">h_name</code>, <code class="constant">h_aliases</code>, and
<code class="constant">h_addr_list</code> elements of the
<span class="type">struct hostent</span> returned in <em class="parameter"><code>resbuf</code></em>.
Successful calls to <code class="function">lwres_gethostbyaddr_r()</code> return
<em class="parameter"><code>resbuf</code></em>, which is a pointer to the
<code class="function">struct hostent()</code> it created.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2543969"></a><h2>RETURN VALUES</h2>
<p>
The functions
<code class="function">lwres_gethostbyname()</code>,
<code class="function">lwres_gethostbyname2()</code>,
<code class="function">lwres_gethostbyaddr()</code>,
and
<code class="function">lwres_gethostent()</code>
return NULL to indicate an error. In this case the global variable
<span class="type">lwres_h_errno</span>
will contain one of the following error codes defined in
<code class="filename">&lt;lwres/netdb.h&gt;</code>:
</p>
<div class="variablelist"><dl>
<dt><span class="term"><code class="constant">HOST_NOT_FOUND</code></span></dt>
<dd><p>
The host or address was not found.
</p></dd>
<dt><span class="term"><code class="constant">TRY_AGAIN</code></span></dt>
<dd><p>
A recoverable error occurred, e.g., a timeout.
Retrying the lookup may succeed.
</p></dd>
<dt><span class="term"><code class="constant">NO_RECOVERY</code></span></dt>
<dd><p>
A non-recoverable error occurred.
</p></dd>
<dt><span class="term"><code class="constant">NO_DATA</code></span></dt>
<dd><p>
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.
</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>
<p><code class="function">lwres_gethostent()</code>
and <code class="function">lwres_gethostent_r()</code>
always return <span class="type">NULL</span>.
</p>
<p>
Successful calls to <code class="function">lwres_gethostbyname_r()</code> and
<code class="function">lwres_gethostbyaddr_r()</code> return
<em class="parameter"><code>resbuf</code></em>, a pointer to the
<span class="type">struct hostent</span> that was initialised by these functions. They return
<span class="type">NULL</span> if the lookups fail or if <em class="parameter"><code>buf</code></em>
was too small to hold the list of addresses and names referenced by
the <code class="constant">h_name</code>, <code class="constant">h_aliases</code>, and
<code class="constant">h_addr_list</code> elements of the
<span class="type">struct hostent</span>.
If <em class="parameter"><code>buf</code></em> was too small, both
<code class="function">lwres_gethostbyname_r()</code> and
<code class="function">lwres_gethostbyaddr_r()</code> set the global
variable
<span class="type">errno</span> to <span class="errorcode">ERANGE</span>.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2544202"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry"><span class="refentrytitle">gethostent</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_getipnode</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_hstrerror</span>(3)</span>
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2544236"></a><h2>BUGS</h2>
<p><code class="function">lwres_gethostbyname()</code>,
<code class="function">lwres_gethostbyname2()</code>,
<code class="function">lwres_gethostbyaddr()</code>
and
<code class="function">lwres_endhostent()</code>
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
<code class="function">lwres_gethostbyname_r()</code>,
and
<code class="function">lwres_gethostbyaddr_r()</code>
respectively.
</p>
<p>
The resolver daemon does not currently support any non-DNS
name services such as
<code class="filename">/etc/hosts</code>
or
<span class="type">NIS</span>,
consequently the above functions don't, either.
</p>
</div>
</div></body>
</html>
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