lwres/man/lwres_gethostent.html

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98N/A<title>lwres_gethostent</title>
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98N/A<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry">
98N/A<a name="id-1"></a><div class="titlepage"></div>
98N/A<div class="refnamediv">
98N/A<h2>Name</h2>
98N/A<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>
98N/A</div>
98N/A<div class="refsynopsisdiv">
98N/A<h2>Synopsis</h2>
98N/A<div class="funcsynopsis">
98N/A<pre class="funcsynopsisinfo">#include &lt;lwres/netdb.h&gt;</pre>
98N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
98N/A<td><code class="funcdef">
98N/Astruct hostent *
98N/A<b class="fsfunc">lwres_gethostbyname</b>(</code></td>
98N/A<td>const char *<var class="pdparam">name</var><code>)</code>;</td>
98N/A</tr></table>
98N/A<div class="funcprototype-spacer">�</div>
98N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
98N/A<tr>
810N/A<td><code class="funcdef">
98N/Astruct hostent *
98N/A<b class="fsfunc">lwres_gethostbyname2</b>(</code></td>
235N/A<td>const char *<var class="pdparam">name</var>, </td>
156N/A</tr>
156N/A<tr>
156N/A<td>�</td>
156N/A<td>int <var class="pdparam">af</var><code>)</code>;</td>
98N/A</tr>
98N/A</table>
98N/A<div class="funcprototype-spacer">�</div>
98N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
493N/A<tr>
493N/A<td><code class="funcdef">
98N/Astruct hostent *
98N/A<b class="fsfunc">lwres_gethostbyaddr</b>(</code></td>
235N/A<td>const char *<var class="pdparam">addr</var>, </td>
493N/A</tr>
98N/A<tr>
98N/A<td>�</td>
98N/A<td>int <var class="pdparam">len</var>, </td>
98N/A</tr>
606N/A<tr>
98N/A<td>�</td>
98N/A<td>int <var class="pdparam">type</var><code>)</code>;</td>
98N/A</tr>
606N/A</table>
606N/A<div class="funcprototype-spacer">�</div>
98N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
493N/A<td><code class="funcdef">
493N/Astruct hostent *
493N/A<b class="fsfunc">lwres_gethostent</b>(</code></td>
98N/A<td>void<code>)</code>;</td>
98N/A</tr></table>
98N/A<div class="funcprototype-spacer">�</div>
98N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
606N/A<td><code class="funcdef">
591N/Avoid
493N/A<b class="fsfunc">lwres_sethostent</b>(</code></td>
493N/A<td>int <var class="pdparam">stayopen</var><code>)</code>;</td>
493N/A</tr></table>
493N/A<div class="funcprototype-spacer">�</div>
493N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
493N/A<td><code class="funcdef">
493N/Avoid
493N/A<b class="fsfunc">lwres_endhostent</b>(</code></td>
493N/A<td>void<code>)</code>;</td>
705N/A</tr></table>
493N/A<div class="funcprototype-spacer">�</div>
557N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
557N/A<tr>
493N/A<td><code class="funcdef">
493N/Astruct hostent *
606N/A<b class="fsfunc">lwres_gethostbyname_r</b>(</code></td>
606N/A<td>const char *<var class="pdparam">name</var>, </td>
98N/A</tr>
810N/A<tr>
810N/A<td>�</td>
591N/A<td>struct hostent *<var class="pdparam">resbuf</var>, </td>
810N/A</tr>
810N/A<tr>
591N/A<td>�</td>
591N/A<td>char *<var class="pdparam">buf</var>, </td>
810N/A</tr>
98N/A<tr>
98N/A<td>�</td>
98N/A<td>int <var class="pdparam">buflen</var>, </td>
98N/A</tr>
98N/A<tr>
606N/A<td>�</td>
98N/A<td>int *<var class="pdparam">error</var><code>)</code>;</td>
606N/A</tr>
98N/A</table>
591N/A<div class="funcprototype-spacer">�</div>
111N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
111N/A<tr>
111N/A<td><code class="funcdef">
111N/Astruct hostent  *
111N/A<b class="fsfunc">lwres_gethostbyaddr_r</b>(</code></td>
606N/A<td>const char *<var class="pdparam">addr</var>, </td>
606N/A</tr>
606N/A<tr>
606N/A<td>�</td>
606N/A<td>int <var class="pdparam">len</var>, </td>
98N/A</tr>
98N/A<tr>
733N/A<td>�</td>
733N/A<td>int <var class="pdparam">type</var>, </td>
733N/A</tr>
733N/A<tr>
733N/A<td>�</td>
606N/A<td>struct hostent *<var class="pdparam">resbuf</var>, </td>
606N/A</tr>
606N/A<tr>
98N/A<td>�</td>
212N/A<td>char *<var class="pdparam">buf</var>, </td>
606N/A</tr>
606N/A<tr>
606N/A<td>�</td>
606N/A<td>int <var class="pdparam">buflen</var>, </td>
606N/A</tr>
212N/A<tr>
98N/A<td>�</td>
98N/A<td>int *<var class="pdparam">error</var><code>)</code>;</td>
98N/A</tr>
98N/A</table>
182N/A<div class="funcprototype-spacer">�</div>
98N/A<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
<tr>
<td><code class="funcdef">
struct hostent  *
<b class="fsfunc">lwres_gethostent_r</b>(</code></td>
<td>struct hostent *<var class="pdparam">resbuf</var>, </td>
</tr>
<tr>
<td>�</td>
<td>char *<var class="pdparam">buf</var>, </td>
</tr>
<tr>
<td>�</td>
<td>int <var class="pdparam">buflen</var>, </td>
</tr>
<tr>
<td>�</td>
<td>int *<var class="pdparam">error</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer">�</div>
<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_sethostent_r</b>(</code></td>
<td>int <var class="pdparam">stayopen</var><code>)</code>;</td>
</tr></table>
<div class="funcprototype-spacer">�</div>
<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_endhostent_r</b>(</code></td>
<td>void<code>)</code>;</td>
</tr></table>
<div class="funcprototype-spacer">�</div>
</div>
</div>
<div class="refsection">
<a name="id-1.7"></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 class="variablelist">
<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="refsection">
<a name="id-1.8"></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 class="variablelist">
<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="refsection">
<a name="id-1.9"></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="refsection">
<a name="id-1.10"></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>
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