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6 .TH GETIPNODEBYNAME 3SOCKET "Aug 22, 2007"
7 .SH NAME
8 getipnodebyname, getipnodebyaddr, freehostent \- get IP node entry
9 .SH SYNOPSIS
10 .LP
11 .nf
12 \fBcc\fR [ \fIflag\fR... ] \fIfile\fR... \fB-lsocket\fR \fB -lnsl \fR [ \fIlibrary\fR... ]
13 #include <sys/socket.h>
14 #include <netdb.h>
15
16 \fBstruct hostent *\fR\fBgetipnodebyname\fR(\fBconst char *\fR\fIname\fR, \fBint\fR \fIaf\fR,
17 \fBint\fR \fIflags\fR, \fBint *\fR\fIerror_num\fR);
18 .fi
19
20 .LP
21 .nf
22 \fBstruct hostent *\fR\fBgetipnodebyaddr\fR(\fBconst void *\fR\fIsrc\fR, \fBsize_t\fR \fIlen\fR,
23 \fBint\fR \fIaf\fR, \fBint *\fR\fIerror_num\fR);
24 .fi
25
26 .LP
27 .nf
28 \fBvoid\fR \fBfreehostent\fR(\fBstruct hostent *\fR\fIptr\fR);
29 .fi
30
31 .SH PARAMETERS
32 .sp
33 .ne 2
34 .na
35 \fB\fIaf\fR\fR
36 .ad
37 .RS 13n
38 Address family
39 .RE
40
41 .sp
42 .ne 2
43 .na
44 \fB\fIflags\fR\fR
45 .ad
46 .RS 13n
47 Various flags
48 .RE
49
50 .sp
51 .ne 2
52 .na
53 \fB\fIname\fR\fR
54 .ad
55 .RS 13n
56 Name of host
57 .RE
58
59 .sp
60 .ne 2
61 .na
62 \fB\fIerror_num\fR\fR
63 .ad
64 .RS 13n
65 Error storage
66 .RE
67
68 .sp
69 .ne 2
70 .na
71 \fB\fIsrc\fR\fR
72 .ad
73 .RS 13n
74 Address for lookup
75 .RE
76
77 .sp
78 .ne 2
79 .na
80 \fB\fIlen\fR\fR
81 .ad
82 .RS 13n
83 Length of address
84 .RE
85
86 .sp
87 .ne 2
88 .na
89 \fB\fIptr\fR\fR
90 .ad
91 .RS 13n
92 Pointer to \fBhostent\fR structure
93 .RE
94
95 .SH DESCRIPTION
96 .sp
97 .LP
98 The \fBgetipnodebyname()\fR function searches the \fBipnodes\fR database from
99 the beginning. The function finds the first \fBh_name\fR member that matches
100 the hostname specified by \fIname\fR. The function takes an \fIaf\fR argument
101 that specifies the address family. The address family can be \fBAF_INET\fR for
102 IPv4 addresses or \fBAF_INET6\fR for IPv6 addresses. The \fIflags\fR argument
103 determines what results are returned based on the value of \fIflags\fR. If the
104 \fIflags\fR argument is set to \fB0\fR (zero), the default operation of the
105 function is specified as follows:
106 .RS +4
107 .TP
108 .ie t \(bu
109 .el o
110 If the \fIaf\fR argument is \fBAF_INET\fR, a query is made for an IPv4 address.
111 If successful, IPv4 addresses are returned and the \fBh_length\fR member of the
112 \fBhostent\fR structure is 4. Otherwise, the function returns a \fINULL\fR
113 pointer.
114 .RE
115 .RS +4
116 .TP
117 .ie t \(bu
118 .el o
119 If the \fIaf\fR argument is \fBAF_INET6\fR, a query is made for an IPv6
120 address. If successful, IPv6 addresses are returned and the \fBh_length\fR
121 member of the \fBhostent\fR structure is 16. Otherwise, the function returns a
122 \fINULL\fR pointer.
123 .RE
124 .sp
125 .LP
126 The \fIflags\fR argument changes the default actions of the function. Set the
127 \fIflags\fR argument with a logical \fBOR\fR operation on any of combination of
128 the following values:
129 .RS +4
130 .TP
131 .ie t \(bu
132 .el o
133 \fBAI_V4MAPPED\fR
134 .RE
135 .RS +4
136 .TP
137 .ie t \(bu
138 .el o
139 \fBAI_ALL\fR
140 .RE
141 .RS +4
142 .TP
143 .ie t \(bu
144 .el o
145 \fBAI_ADDRCONFIG\fR
146 .RE
147 .sp
148 .LP
149 The special flags value, \fBAI_DEFAULT\fR, should handle most applications.
150 Porting simple applications to use IPv6 replaces the call
151 .sp
152 .in +2
153 .nf
154 hptr = gethostbyname(name);
155 .fi
156 .in -2
157
158 .sp
159 .LP
160 with
161 .sp
162 .in +2
163 .nf
164 hptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num);
165 .fi
166 .in -2
167
168 .sp
169 .LP
170 The \fIflags\fR value \fB0\fR (zero) implies a strict interpretation of the
171 \fIaf\fR argument:
172 .RS +4
173 .TP
174 .ie t \(bu
175 .el o
176 If \fIflags\fR is \fB0\fR and \fIaf\fR is \fBAF_INET\fR, the caller wants only
177 IPv4 addresses. A query is made for \fBA\fR records. If successful, IPv4
178 addresses are returned and the \fBh_length\fR member of the \fBhostent\fR
179 structure is 4. Otherwise, the function returns a \fINULL\fR pointer.
180 .RE
181 .RS +4
182 .TP
183 .ie t \(bu
184 .el o
185 If \fIflags\fR is \fB0\fR and \fIaf\fR is \fBAF_INET6\fR, the caller wants only
186 IPv6 addresses. A query is made for \fBAAAA\fR records. If successful, IPv6
187 addresses are returned and the \fBh_length\fR member of the \fBhostent\fR
188 structure is 16. Otherwise, the function returns a \fINULL\fR pointer.
189 .RE
190 .sp
191 .LP
192 Logically \fBOR\fR other constants into the \fIflags\fR argument to modify the
193 behavior of the \fBgetipnodebyname()\fR function.
194 .RS +4
195 .TP
196 .ie t \(bu
197 .el o
198 If the \fBAI_V4MAPPED\fR flag is specified with \fIaf\fR set to \fBAF_INET6\fR,
199 the caller can accept IPv4-mapped IPv6 addresses. If no \fBAAAA\fR records are
200 found, a query is made for \fBA\fR records. Any \fBA\fR records found are
201 returned as IPv4-mapped IPv6 addresses and the \fBh_length\fR is 16. The
202 \fBAI_V4MAPPED\fR flag is ignored unless \fIaf\fR equals \fBAF_INET6\fR.
203 .RE
204 .RS +4
205 .TP
206 .ie t \(bu
207 .el o
208 The \fBAI_ALL\fR flag is used in conjunction with the \fBAI_V4MAPPED\fR flag,
209 exclusively with the IPv6 address family. When \fBAI_ALL\fR is logically
210 \fBOR\fRed with \fBAI_V4MAPPED\fR flag, the caller wants all addresses: IPv6
211 and IPv4-mapped IPv6 addresses. A query is first made for \fBAAAA\fR records
212 and, if successful, IPv6 addresses are returned. Another query is then made for
213 \fBA\fR records. Any \fBA\fR records found are returned as IPv4-mapped IPv6
214 addresses and the \fBh_length\fR is 16. Only when both queries fail does the
215 function return a \fINULL\fR pointer. The \fBAI_ALL\fR flag is ignored unless
216 \fIaf\fR is set to \fBAF_INET6\fR.
217 .RE
218 .RS +4
219 .TP
220 .ie t \(bu
221 .el o
222 The \fBAI_ADDRCONFIG\fR flag specifies that a query for \fBAAAA\fR records
223 should occur only when the node is configured with at least one IPv6 source
224 address. A query for \fBA\fR records should occur only when the node is
225 configured with at least one IPv4 source address. For example, if a node is
226 configured with no IPv6 source addresses, \fIaf\fR equals \fBAF_INET6\fR, and
227 the node name queried has both \fBAAAA\fR and \fBA\fR records, then:
228 .RS +4
229 .TP
230 .ie t \(bu
231 .el o
232 A \fINULL\fR pointer is returned when only the \fBAI_ADDRCONFIG\fR value is
233 specified.
234 .RE
235 .RS +4
236 .TP
237 .ie t \(bu
238 .el o
239 The \fBA\fR records are returned as IPv4-mapped IPv6 addresses when the
240 \fBAI_ADDRCONFIG\fR and \fBAI_V4MAPPED\fR values are specified.
241 .RE
242 .RE
243 .sp
244 .LP
245 The special flags value, \fBAI_DEFAULT\fR, is defined as
246 .sp
247 .in +2
248 .nf
249 #define AI_DEFAULT (AI_V4MAPPED | AI_ADDRCONFIG)
250 .fi
251 .in -2
252
253 .sp
254 .LP
255 The \fBgetipnodebyname()\fR function allows the \fIname\fR argument to be a
256 node name or a literal address string: a dotted-decimal IPv4 address or an IPv6
257 hex address. Applications do not have to call \fBinet_pton\fR(3SOCKET) to
258 handle literal address strings.
259 .sp
260 .LP
261 Four scenarios arise based on the type of literal address string and the value
262 of the \fIaf\fR argument. The two simple cases occur when \fIname\fR is a
263 dotted-decimal IPv4 address and \fIaf\fR equals \fBAF_INET\fR and when
264 \fIname\fR is an IPv6 hex address and \fIaf\fR equals \fBAF_INET6\fR. The
265 members of the returned \fBhostent\fR structure are:
266 .sp
267 .ne 2
268 .na
269 \fB\fBh_name\fR\fR
270 .ad
271 .RS 15n
272 Pointer to a copy of the name argument
273 .RE
274
275 .sp
276 .ne 2
277 .na
278 \fB\fBh_aliases\fR\fR
279 .ad
280 .RS 15n
281 \fINULL\fR pointer.
282 .RE
283
284 .sp
285 .ne 2
286 .na
287 \fB\fBh_addrtype\fR\fR
288 .ad
289 .RS 15n
290 Copy of the \fIaf\fR argument.
291 .RE
292
293 .sp
294 .ne 2
295 .na
296 \fB\fBh_length\fR\fR
297 .ad
298 .RS 15n
299 4 for \fBAF_INET\fR or 16 for \fBAF_INET6\fR.
300 .RE
301
302 .sp
303 .ne 2
304 .na
305 \fB\fBh_addr_list\fR\fR
306 .ad
307 .RS 15n
308 Array of pointers to 4-byte or 16-byte binary addresses. The array is
309 terminated by a \fINULL\fR pointer.
310 .RE
311
312 .SH RETURN VALUES
313 .sp
314 .LP
315 Upon successful completion, \fBgetipnodebyname()\fR and \fBgetipnodebyaddr()\fR
316 return a \fBhostent\fR structure. Otherwise they return \fINULL\fR.
317 .sp
318 .LP
319 The \fBhostent\fR structure does not change from the existing definition when
320 used with \fBgethostbyname\fR(3NSL). For example, host entries are represented
321 by the \fBstruct hostent\fR structure defined in <\fBnetdb.h\fR>:
322 .sp
323 .in +2
324 .nf
325 struct hostent {
326 char *h_name; /* canonical name of host */
327 char **h_aliases; /* alias list */
328 int h_addrtype; /* host address type */
329 int h_length; /* length of address */
330 char **h_addr_list; /* list of addresses */
331 };
332 .fi
333 .in -2
334
335 .sp
336 .LP
337 An error occurs when \fIname\fR is an IPv6 hex address and \fIaf\fR equals
338 \fBAF_INET\fR. The return value of the function is a \fINULL\fR pointer and
339 \fBerror_num\fR equals \fBHOST_NOT_FOUND\fR.
340 .sp
341 .LP
342 The \fBgetipnodebyaddr()\fR function has the same arguments as the existing
343 \fBgethostbyaddr\fR(3NSL) function, but adds an error number. As with
344 \fBgetipnodebyname()\fR, \fBgetipnodebyaddr()\fR is thread-safe. The
345 \fBerror_num\fR value is returned to the caller with the appropriate error code
346 to support thread-safe error code returns. The following error conditions can
347 be returned for \fBerror_num\fR:
348 .sp
349 .ne 2
350 .na
351 \fB\fBHOST_NOT_FOUND\fR\fR
352 .ad
353 .RS 18n
354 Host is unknown.
355 .RE
356
357 .sp
358 .ne 2
359 .na
360 \fB\fBNO_DATA\fR\fR
361 .ad
362 .RS 18n
363 No address is available for the \fIname\fR specified in the server request.
364 This error is not a soft error. Another type of \fIname\fR server request might
365 be successful.
366 .RE
367
368 .sp
369 .ne 2
370 .na
371 \fB\fBNO_RECOVERY\fR\fR
372 .ad
373 .RS 18n
374 An unexpected server failure occurred, which is a non-recoverable error.
375 .RE
376
377 .sp
378 .ne 2
379 .na
380 \fB\fBTRY_AGAIN\fR\fR
381 .ad
382 .RS 18n
383 This error is a soft error that indicates that the local server did not receive
384 a response from an authoritative server. A retry at some later time might be
385 successful.
386 .RE
387
388 .sp
389 .LP
390 One possible source of confusion is the handling of IPv4-mapped IPv6 addresses
391 and IPv4-compatible IPv6 addresses, but the following logic should apply:
392 .RS +4
393 .TP
394 1.
395 If \fIaf\fR is \fBAF_INET6\fR, and if \fIlen\fR equals 16, and if the IPv6
396 address is an IPv4-mapped IPv6 address or an IPv4-compatible IPv6 address, then
397 skip over the first 12 bytes of the IPv6 address, set \fIaf\fR to
398 \fBAF_INET\fR, and set \fIlen\fR to 4.
399 .RE
400 .RS +4
401 .TP
402 2.
403 If \fIaf\fR is \fBAF_INET\fR, lookup the \fIname\fR for the given IPv4
404 address.
405 .RE
406 .RS +4
407 .TP
408 3.
409 If \fIaf\fR is \fBAF_INET6\fR, lookup the \fIname\fR for the given IPv6
410 address.
411 .RE
412 .RS +4
413 .TP
414 4.
415 If the function is returning success, then the single address that is
416 returned in the \fBhostent\fR structure is a copy of the first argument to the
417 function with the same address family that was passed as an argument to this
418 function.
419 .RE
420 .sp
421 .LP
422 All four steps listed are performed in order.
423 .sp
424 .LP
425 This structure, and the information pointed to by this structure, are
426 dynamically allocated by \fBgetipnodebyname()\fR and \fBgetipnodebyaddr()\fR.
427 The \fBfreehostent()\fR function frees this memory.
428 .SH EXAMPLES
429 .LP
430 \fBExample 1 \fRGetting the Canonical Name, Aliases, and Internet IP Addresses
431 for a Given Hostname
432 .sp
433 .LP
434 The following is a sample program that retrieves the canonical name, aliases,
435 and all Internet IP addresses, both version 6 and version 4, for a given
436 hostname.
437
438 .sp
439 .in +2
440 .nf
441 #include <stdio.h>
442 #include <string.h>
443 #include <sys/types.h>
444 #include <sys/socket.h>
445 #include <netinet/in.h>
446 #include <arpa/inet.h>
447 #include <netdb.h>
448
449 main(int argc, const char **argv)
450 {
451 char abuf[INET6_ADDRSTRLEN];
452 int error_num;
453 struct hostent *hp;
454 char **p;
455
456 if (argc != 2) {
457 (void) printf("usage: %s hostname\n", argv[0]);
458 exit (1);
459 }
460
461 /* argv[1] can be a pointer to a hostname or literal IP address */
462 hp = getipnodebyname(argv[1], AF_INET6, AI_ALL | AI_ADDRCONFIG |
463 AI_V4MAPPED, &error_num);
464 if (hp == NULL) {
465 if (error_num == TRY_AGAIN) {
466 printf("%s: unknown host or invalid literal address "
467 "(try again later)\n", argv[1]);
468 } else {
469 printf("%s: unknown host or invalid literal address\n",
470 argv[1]);
471 }
472 exit (1);
473 }
474 for (p = hp->h_addr_list; *p != 0; p++) {
475 struct in6_addr in6;
476 char **q;
477
478 bcopy(*p, (caddr_t)&in6, hp->h_length);
479 (void) printf("%s\t%s", inet_ntop(AF_INET6, (void *)&in6,
480 abuf, sizeof(abuf)), hp->h_name);
481 for (q = hp->h_aliases; *q != 0; q++)
482 (void) printf(" %s", *q);
483 (void) putchar('\n');
484 }
485 freehostent(hp);
486 exit (0);
487 }
488 .fi
489 .in -2
490
491 .SH ATTRIBUTES
492 .sp
493 .LP
494 See \fBattributes\fR(5) for descriptions of the following attributes:
495 .sp
496
497 .sp
498 .TS
499 box;
500 c | c
501 l | l .
502 ATTRIBUTE TYPE ATTRIBUTE VALUE
503 _
504 Interface Stability Committed
505 _
506 MT-Level Safe
507 .TE
508
509 .SH SEE ALSO
510 .sp
511 .LP
512 \fBgetaddrinfo\fR(3SOCKET), \fBgethostbyname\fR(3NSL), \fBhtonl\fR(3SOCKET),
513 \fBinet\fR(3SOCKET), \fBnetdb.h\fR(3HEAD), \fBhosts\fR(4),
514 \fBnsswitch.conf\fR(4), \fBattributes\fR(5)
515 .SH NOTES
516 .sp
517 .LP
518 No enumeration functions are provided for IPv6. Existing enumeration functions
519 such as \fBsethostent\fR(3NSL) do not work in combination with the
520 \fBgetipnodebyname()\fR and \fBgetipnodebyaddr()\fR functions.
521 .sp
522 .LP
523 All the functions that return a \fBstruct hostent\fR must always return the
524 canonical in the \fBh_name\fR field. This name, by definition, is the
525 well-known and official hostname shared between all aliases and all addresses.
526 The underlying source that satisfies the request determines the mapping of the
527 input name or address into the set of names and addresses in \fBhostent\fR.
528 Different sources might make such as determination in different ways. If more
529 than one alias and more than one address in \fBhostent\fR exist, no pairing is
530 implied between the alias and address.
531 .sp
532 .LP
533 The current implementations of these functions return or accept only addresses
534 for the Internet address family (type \fBAF_INET\fR) or the Internet address
535 family Version 6 (type \fBAF_INET6\fR).
536 .sp
537 .LP
538 IPv4-mapped addresses are not recommended. The \fBgetaddrinfo\fR(3SOCKET)
539 function is preferred over \fBgetipnodebyaddr()\fR because it allows
540 applications to lookup IPv4 and IPv6 addresses without relying on IPv4-mapped
541 addresses.
542 .sp
543 .LP
544 The form for an address of type \fBAF_INET\fR is a \fBstruct in_addr\fR defined
545 in <\fBnetinet/in.h\fR>. The form for an address of type \fBAF_INET6\fR is a
546 \fBstruct in6_addr\fR, also defined in <\fBnetinet/in.h\fR>. The functions
547 described in \fBinet_ntop\fR(3SOCKET) and \fBinet_pton\fR(3SOCKET) that are
548 illustrated in the EXAMPLES section are helpful in constructing and
549 manipulating addresses in either of these forms.