2 - Copyright (C) 2004, 2005 Internet Systems Consortium, Inc. ("ISC")
3 - Copyright (C) 2001 Internet Software Consortium.
5 - Permission to use, copy, modify, and distribute this software for any
6 - purpose with or without fee is hereby granted, provided that the above
7 - copyright notice and this permission notice appear in all copies.
9 - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
10 - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
11 - AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
12 - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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25 <a name=
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26 <div class=
"refnamediv">
28 <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>
30 <div class=
"refsynopsisdiv">
32 <div class=
"funcsynopsis">
33 <pre class=
"funcsynopsisinfo">#include
<lwres/netdb.h
></pre>
34 <table border=
"0" summary=
"Function synopsis" cellspacing=
"0" cellpadding=
"0" style=
"padding-bottom: 1em">
36 <td><code class=
"funcdef">
38 <b class=
"fsfunc">lwres_gethostbyname
</b>(
</code></td>
50 <table border=
"0" summary=
"Function synopsis" cellspacing=
"0" cellpadding=
"0" style=
"padding-bottom: 1em">
52 <td><code class=
"funcdef">
54 <b class=
"fsfunc">lwres_gethostbyname2
</b>(
</code></td>
70 <table border=
"0" summary=
"Function synopsis" cellspacing=
"0" cellpadding=
"0" style=
"padding-bottom: 1em">
72 <td><code class=
"funcdef">
74 <b class=
"fsfunc">lwres_gethostbyaddr
</b>(
</code></td>
95 <p><code class=
"funcdef">
97 <b class=
"fsfunc">lwres_gethostent
</b>(
</code>void
<code>)
</code>;
</p>
98 <p><code class=
"funcdef">
100 <b class=
"fsfunc">lwres_sethostent
</b>(
</code>int stayopen
<code>)
</code>;
</p>
101 <p><code class=
"funcdef">
103 <b class=
"fsfunc">lwres_endhostent
</b>(
</code>void
<code>)
</code>;
</p>
104 <table border=
"0" summary=
"Function synopsis" cellspacing=
"0" cellpadding=
"0" style=
"padding-bottom: 1em">
106 <td><code class=
"funcdef">
108 <b class=
"fsfunc">lwres_gethostbyname_r
</b>(
</code></td>
139 <table border=
"0" summary=
"Function synopsis" cellspacing=
"0" cellpadding=
"0" style=
"padding-bottom: 1em">
141 <td><code class=
"funcdef">
143 <b class=
"fsfunc">lwres_gethostbyaddr_r
</b>(
</code></td>
184 <table border=
"0" summary=
"Function synopsis" cellspacing=
"0" cellpadding=
"0" style=
"padding-bottom: 1em">
186 <td><code class=
"funcdef">
188 <b class=
"fsfunc">lwres_gethostent_r
</b>(
</code></td>
214 <p><code class=
"funcdef">
216 <b class=
"fsfunc">lwres_sethostent_r
</b>(
</code>int stayopen
<code>)
</code>;
</p>
217 <p><code class=
"funcdef">
219 <b class=
"fsfunc">lwres_endhostent_r
</b>(
</code>void
<code>)
</code>;
</p>
222 <div class=
"refsect1" lang=
"en">
223 <a name=
"id2549606"></a><h2>DESCRIPTION
</h2>
225 These functions provide hostname-to-address and
226 address-to-hostname lookups by means of the lightweight resolver.
227 They are similar to the standard
228 <span class=
"citerefentry"><span class=
"refentrytitle">gethostent
</span>(
3
230 functions provided by most operating systems.
232 <span class=
"type">struct hostent
</span>
233 which is usually defined in
234 <code class=
"filename"><namedb.h
></code>.
237 <pre class=
"programlisting">
239 char *h_name; /* official name of host */
240 char **h_aliases; /* alias list */
241 int h_addrtype; /* host address type */
242 int h_length; /* length of address */
243 char **h_addr_list; /* list of addresses from name server */
245 #define h_addr h_addr_list[
0] /* address, for backward compatibility */
250 The members of this structure are:
252 <div class=
"variablelist"><dl>
253 <dt><span class=
"term"><code class=
"constant">h_name
</code></span></dt>
255 The official (canonical) name of the host.
257 <dt><span class=
"term"><code class=
"constant">h_aliases
</code></span></dt>
259 A NULL-terminated array of alternate names (nicknames) for the host.
261 <dt><span class=
"term"><code class=
"constant">h_addrtype
</code></span></dt>
263 The type of address being returned
—
264 <span class=
"type">PF_INET
</span>
266 <span class=
"type">PF_INET6
</span>.
268 <dt><span class=
"term"><code class=
"constant">h_length
</code></span></dt>
270 The length of the address in bytes.
272 <dt><span class=
"term"><code class=
"constant">h_addr_list
</code></span></dt>
274 A
<span class=
"type">NULL
</span>
275 terminated array of network addresses for the host.
276 Host addresses are returned in network byte order.
282 For backward compatibility with very old software,
283 <code class=
"constant">h_addr
</code>
284 is the first address in
285 <code class=
"constant">h_addr_list.
</code>
288 <code class=
"function">lwres_gethostent()
</code>,
289 <code class=
"function">lwres_sethostent()
</code>,
290 <code class=
"function">lwres_endhostent()
</code>,
291 <code class=
"function">lwres_gethostent_r()
</code>,
292 <code class=
"function">lwres_sethostent_r()
</code>
294 <code class=
"function">lwres_endhostent_r()
</code>
295 provide iteration over the known host entries on systems that
296 provide such functionality through facilities like
297 <code class=
"filename">/etc/hosts
</code>
298 or NIS. The lightweight resolver does not currently implement
299 these functions; it only provides them as stub functions that always
303 <code class=
"function">lwres_gethostbyname()
</code> and
304 <code class=
"function">lwres_gethostbyname2()
</code> look up the hostname
305 <em class=
"parameter"><code>name
</code></em>.
306 <code class=
"function">lwres_gethostbyname()
</code> always looks for an IPv4
307 address while
<code class=
"function">lwres_gethostbyname2()
</code> looks for an
308 address of protocol family
<em class=
"parameter"><code>af
</code></em>: either
309 <span class=
"type">PF_INET
</span> or
<span class=
"type">PF_INET6
</span> — IPv4 or IPV6
310 addresses respectively. Successful calls of the functions return a
311 <span class=
"type">struct hostent
</span>for the name that was looked up.
312 <span class=
"type">NULL
</span> is returned if the lookups by
313 <code class=
"function">lwres_gethostbyname()
</code> or
314 <code class=
"function">lwres_gethostbyname2()
</code> fail.
317 Reverse lookups of addresses are performed by
318 <code class=
"function">lwres_gethostbyaddr()
</code>.
319 <em class=
"parameter"><code>addr
</code></em> is an address of length
320 <em class=
"parameter"><code>len
</code></em> bytes and protocol family
321 <em class=
"parameter"><code>type
</code></em> — <span class=
"type">PF_INET
</span> or
322 <span class=
"type">PF_INET6
</span>.
323 <code class=
"function">lwres_gethostbyname_r()
</code> is a thread-safe function
324 for forward lookups. If an error occurs, an error code is returned in
325 <em class=
"parameter"><code>*error
</code></em>.
326 <em class=
"parameter"><code>resbuf
</code></em> is a pointer to a
<span class=
"type">struct
327 hostent
</span> which is initialised by a successful call to
328 <code class=
"function">lwres_gethostbyname_r()
</code> .
329 <em class=
"parameter"><code>buf
</code></em> is a buffer of length
330 <em class=
"parameter"><code>len
</code></em> bytes which is used to store the
331 <code class=
"constant">h_name
</code>,
<code class=
"constant">h_aliases
</code>, and
332 <code class=
"constant">h_addr_list
</code> elements of the
<span class=
"type">struct
333 hostent
</span> returned in
<em class=
"parameter"><code>resbuf
</code></em>.
334 Successful calls to
<code class=
"function">lwres_gethostbyname_r()
</code>
335 return
<em class=
"parameter"><code>resbuf
</code></em>,
336 which is a pointer to the
<span class=
"type">struct hostent
</span> it created.
339 <code class=
"function">lwres_gethostbyaddr_r()
</code> is a thread-safe function
340 that performs a reverse lookup of address
<em class=
"parameter"><code>addr
</code></em>
341 which is
<em class=
"parameter"><code>len
</code></em> bytes long and is of protocol
342 family
<em class=
"parameter"><code>type
</code></em> — <span class=
"type">PF_INET
</span> or
343 <span class=
"type">PF_INET6
</span>. If an error occurs, the error code is returned
344 in
<em class=
"parameter"><code>*error
</code></em>. The other function parameters are
345 identical to those in
<code class=
"function">lwres_gethostbyname_r()
</code>.
346 <em class=
"parameter"><code>resbuf
</code></em> is a pointer to a
<span class=
"type">struct
347 hostent
</span> which is initialised by a successful call to
348 <code class=
"function">lwres_gethostbyaddr_r()
</code>.
349 <em class=
"parameter"><code>buf
</code></em> is a buffer of length
350 <em class=
"parameter"><code>len
</code></em> bytes which is used to store the
351 <code class=
"constant">h_name
</code>,
<code class=
"constant">h_aliases
</code>, and
352 <code class=
"constant">h_addr_list
</code> elements of the
<span class=
"type">struct
353 hostent
</span> returned in
<em class=
"parameter"><code>resbuf
</code></em>. Successful
354 calls to
<code class=
"function">lwres_gethostbyaddr_r()
</code> return
355 <em class=
"parameter"><code>resbuf
</code></em>, which is a pointer to the
356 <code class=
"function">struct hostent()
</code> it created.
359 <div class=
"refsect1" lang=
"en">
360 <a name=
"id2550013"></a><h2>RETURN VALUES
</h2>
363 <code class=
"function">lwres_gethostbyname()
</code>,
364 <code class=
"function">lwres_gethostbyname2()
</code>,
365 <code class=
"function">lwres_gethostbyaddr()
</code>,
367 <code class=
"function">lwres_gethostent()
</code>
368 return NULL to indicate an error. In this case the global variable
369 <span class=
"type">lwres_h_errno
</span>
370 will contain one of the following error codes defined in
371 <code class=
"filename"><lwres/netdb.h
></code>:
374 <div class=
"variablelist"><dl>
375 <dt><span class=
"term"><code class=
"constant">HOST_NOT_FOUND
</code></span></dt>
377 The host or address was not found.
379 <dt><span class=
"term"><code class=
"constant">TRY_AGAIN
</code></span></dt>
381 A recoverable error occurred, e.g., a timeout.
382 Retrying the lookup may succeed.
384 <dt><span class=
"term"><code class=
"constant">NO_RECOVERY
</code></span></dt>
386 A non-recoverable error occurred.
388 <dt><span class=
"term"><code class=
"constant">NO_DATA
</code></span></dt>
390 The name exists, but has no address information
391 associated with it (or vice versa in the case
392 of a reverse lookup). The code NO_ADDRESS
393 is accepted as a synonym for NO_DATA for backwards
400 <span class=
"citerefentry"><span class=
"refentrytitle">lwres_hstrerror
</span>(
3
402 translates these error codes to suitable error messages.
405 <code class=
"function">lwres_gethostent()
</code>
407 <code class=
"function">lwres_gethostent_r()
</code>
409 <span class=
"type">NULL
</span>.
412 Successful calls to
<code class=
"function">lwres_gethostbyname_r()
</code> and
413 <code class=
"function">lwres_gethostbyaddr_r()
</code> return
414 <em class=
"parameter"><code>resbuf
</code></em>, a pointer to the
<span class=
"type">struct
415 hostent
</span> that was initialised by these functions. They return
416 <span class=
"type">NULL
</span> if the lookups fail or if
<em class=
"parameter"><code>buf
</code></em>
417 was too small to hold the list of addresses and names referenced by
418 the
<code class=
"constant">h_name
</code>,
<code class=
"constant">h_aliases
</code>, and
419 <code class=
"constant">h_addr_list
</code> elements of the
<span class=
"type">struct
420 hostent
</span>. If
<em class=
"parameter"><code>buf
</code></em> was too small, both
421 <code class=
"function">lwres_gethostbyname_r()
</code> and
422 <code class=
"function">lwres_gethostbyaddr_r()
</code> set the global variable
423 <span class=
"type">errno
</span> to
<span class=
"errorcode">ERANGE
</span>.
426 <div class=
"refsect1" lang=
"en">
427 <a name=
"id2550173"></a><h2>SEE ALSO
</h2>
429 <span class=
"citerefentry"><span class=
"refentrytitle">gethostent
</span>(
3)
</span>,
431 <span class=
"citerefentry"><span class=
"refentrytitle">lwres_getipnode
</span>(
3)
</span>,
433 <span class=
"citerefentry"><span class=
"refentrytitle">lwres_hstrerror
</span>(
3
437 <div class=
"refsect1" lang=
"en">
438 <a name=
"id2550209"></a><h2>BUGS
</h2>
440 <code class=
"function">lwres_gethostbyname()
</code>,
441 <code class=
"function">lwres_gethostbyname2()
</code>,
442 <code class=
"function">lwres_gethostbyaddr()
</code>
444 <code class=
"function">lwres_endhostent()
</code>
445 are not thread safe; they return pointers to static data and
446 provide error codes through a global variable.
447 Thread-safe versions for name and address lookup are provided by
448 <code class=
"function">lwres_gethostbyname_r()
</code>,
450 <code class=
"function">lwres_gethostbyaddr_r()
</code>
454 The resolver daemon does not currently support any non-DNS
455 name services such as
456 <code class=
"filename">/etc/hosts
</code>
458 <span class=
"type">NIS
</span>,
459 consequently the above functions don't, either.