lwres_gethostent.html [plain text]
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<title>lwres_gethostent</title>
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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_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 — lightweight resolver get network host entry</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_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="id2543612"></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"><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 —
<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> — 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> — <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> — <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="id2543963"></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"><lwres/netdb.h></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="id2544197"></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="id2544231"></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>
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