| blob | 80488ec50d6cec1550f36478ed7f9cadea7d4bf5 |
1 .\" Copyright (c) 2007, 2008 Michael Kerrisk <mtk.manpages@gmail.com>
2 .\" and Copyright (c) 2006 Ulrich Drepper <drepper@redhat.com>
3 .\" A few pieces of an earlier version remain:
4 .\" Copyright 2000, Sam Varshavchik <mrsam@courier-mta.com>
5 .\"
6 .\" %%%LICENSE_START(VERBATIM)
7 .\" Permission is granted to make and distribute verbatim copies of this
8 .\" manual provided the copyright notice and this permission notice are
9 .\" preserved on all copies.
10 .\"
11 .\" Permission is granted to copy and distribute modified versions of this
12 .\" manual under the conditions for verbatim copying, provided that the
13 .\" entire resulting derived work is distributed under the terms of a
14 .\" permission notice identical to this one.
15 .\"
16 .\" Since the Linux kernel and libraries are constantly changing, this
17 .\" manual page may be incorrect or out-of-date. The author(s) assume no
18 .\" responsibility for errors or omissions, or for damages resulting from
19 .\" the use of the information contained herein. The author(s) may not
20 .\" have taken the same level of care in the production of this manual,
21 .\" which is licensed free of charge, as they might when working
22 .\" professionally.
23 .\"
24 .\" Formatted or processed versions of this manual, if unaccompanied by
25 .\" the source, must acknowledge the copyright and authors of this work.
26 .\" %%%LICENSE_END
27 .\"
28 .\" References: RFC 2553
29 .\"
30 .\" 2005-08-09, mtk, added AI_ALL, AI_ADDRCONFIG, AI_V4MAPPED,
31 .\" and AI_NUMERICSERV.
32 .\" 2006-11-25, Ulrich Drepper <drepper@redhat.com>
33 .\" Add text describing Internationalized Domain Name extensions.
34 .\" 2007-06-08, mtk: added example programs
35 .\" 2008-02-26, mtk; clarify discussion of NULL 'hints' argument; other
36 .\" minor rewrites.
37 .\" 2008-06-18, mtk: many parts rewritten
38 .\" 2008-12-04, Petr Baudis <pasky@suse.cz>
39 .\" Describe results ordering and reference /etc/gai.conf.
40 .\"
41 .\" FIXME . glibc's 2.9 NEWS file documents DCCP and UDP-lite support
42 .\" and is SCTP support now also there?
43 .\"
44 .TH GETADDRINFO 3 2019-03-06 "GNU" "Linux Programmer's Manual"
45 .SH NAME
46 getaddrinfo, freeaddrinfo, gai_strerror \- network address and
47 service translation
48 .SH SYNOPSIS
49 .nf
50 .B #include <sys/types.h>
51 .B #include <sys/socket.h>
52 .B #include <netdb.h>
53 .PP
54 .BI "int getaddrinfo(const char *" "node" ", const char *" "service" ,
55 .BI " const struct addrinfo *" "hints" ,
56 .BI " struct addrinfo **" "res" );
57 .PP
58 .BI "void freeaddrinfo(struct addrinfo *" "res" );
59 .PP
60 .BI "const char *gai_strerror(int " "errcode" );
61 .fi
62 .PP
63 .in -4n
64 Feature Test Macro Requirements for glibc (see
65 .BR feature_test_macros (7)):
66 .ad l
67 .in
68 .PP
69 .BR getaddrinfo (),
70 .BR freeaddrinfo (),
71 .BR gai_strerror ():
72 Since glibc 2.22: _POSIX_C_SOURCE >= 200112L
73 Glibc 2.21 and earlier: _POSIX_C_SOURCE
74 .ad b
75 .SH DESCRIPTION
76 Given
77 .I node
78 and
79 .IR service ,
80 which identify an Internet host and a service,
81 .BR getaddrinfo ()
82 returns one or more
83 .I addrinfo
84 structures, each of which contains an Internet address
85 that can be specified in a call to
86 .BR bind (2)
87 or
88 .BR connect (2).
89 The
90 .BR getaddrinfo ()
91 function combines the functionality provided by the
92 .\" .BR getipnodebyname (3),
93 .\" .BR getipnodebyaddr (3),
94 .BR gethostbyname (3)
95 and
96 .BR getservbyname (3)
97 functions into a single interface, but unlike the latter functions,
98 .BR getaddrinfo ()
99 is reentrant and allows programs to eliminate IPv4-versus-IPv6 dependencies.
100 .PP
101 The
102 .I addrinfo
103 structure used by
104 .BR getaddrinfo ()
105 contains the following fields:
106 .PP
107 .in +4n
108 .EX
109 struct addrinfo {
110 int ai_flags;
111 int ai_family;
112 int ai_socktype;
113 int ai_protocol;
114 socklen_t ai_addrlen;
115 struct sockaddr *ai_addr;
116 char *ai_canonname;
117 struct addrinfo *ai_next;
118 };
119 .EE
120 .in
121 .PP
122 The
123 .I hints
124 argument points to an
125 .I addrinfo
126 structure that specifies criteria for selecting the socket address
127 structures returned in the list pointed to by
128 .IR res .
129 If
130 .I hints
131 is not NULL it points to an
132 .I addrinfo
133 structure whose
134 .IR ai_family ,
135 .IR ai_socktype ,
136 and
137 .I ai_protocol
138 specify criteria that limit the set of socket addresses returned by
139 .BR getaddrinfo (),
140 as follows:
141 .TP 12
142 .I ai_family
143 This field specifies the desired address family for the returned addresses.
144 Valid values for this field include
145 .BR AF_INET
146 and
147 .BR AF_INET6 .
148 The value
149 .B AF_UNSPEC
150 indicates that
151 .BR getaddrinfo ()
152 should return socket addresses for any address family
153 (either IPv4 or IPv6, for example) that can be used with
154 .I node
155 and
156 .IR service .
157 .TP
158 .I ai_socktype
159 This field specifies the preferred socket type, for example
160 .BR SOCK_STREAM
161 or
162 .BR SOCK_DGRAM .
163 Specifying 0 in this field indicates that socket addresses of any type
164 can be returned by
165 .BR getaddrinfo ().
166 .TP
167 .I ai_protocol
168 This field specifies the protocol for the returned socket addresses.
169 Specifying 0 in this field indicates that socket addresses with
170 any protocol can be returned by
171 .BR getaddrinfo ().
172 .TP
173 .I ai_flags
174 This field specifies additional options, described below.
175 Multiple flags are specified by bitwise OR-ing them together.
176 .PP
177 All the other fields in the structure pointed to by
178 .I hints
179 must contain either 0 or a null pointer, as appropriate.
180 .PP
181 Specifying
182 .I hints
183 as NULL is equivalent to setting
184 .I ai_socktype
185 and
186 .I ai_protocol
187 to 0;
188 .I ai_family
189 to
190 .BR AF_UNSPEC ;
191 and
192 .I ai_flags
193 to
194 .BR "(AI_V4MAPPED\ |\ AI_ADDRCONFIG)" .
195 (POSIX specifies different defaults for
196 .IR ai_flags ;
197 see NOTES.)
198 .I node
199 specifies either a numerical network address
200 (for IPv4, numbers-and-dots notation as supported by
201 .BR inet_aton (3);
202 for IPv6, hexadecimal string format as supported by
203 .BR inet_pton (3)),
204 or a network hostname, whose network addresses are looked up and resolved.
205 If
206 .I hints.ai_flags
207 contains the
208 .B AI_NUMERICHOST
209 flag, then
210 .I node
211 must be a numerical network address.
212 The
213 .B AI_NUMERICHOST
214 flag suppresses any potentially lengthy network host address lookups.
215 .PP
216 If the
217 .B AI_PASSIVE
218 flag is specified in
219 .IR hints.ai_flags ,
220 and
221 .I node
222 is NULL,
223 then the returned socket addresses will be suitable for
224 .BR bind (2)ing
225 a socket that will
226 .BR accept (2)
227 connections.
228 The returned socket address will contain the "wildcard address"
229 .RB ( INADDR_ANY
230 for IPv4 addresses,
231 .BR IN6ADDR_ANY_INIT
232 for IPv6 address).
233 The wildcard address is used by applications (typically servers)
234 that intend to accept connections on any of the host's network addresses.
235 If
236 .I node
237 is not NULL, then the
238 .B AI_PASSIVE
239 flag is ignored.
240 .PP
241 If the
242 .B AI_PASSIVE
243 flag is not set in
244 .IR hints.ai_flags ,
245 then the returned socket addresses will be suitable for use with
246 .BR connect (2),
247 .BR sendto (2),
248 or
249 .BR sendmsg (2).
250 If
251 .I node
252 is NULL,
253 then the network address will be set to the loopback interface address
254 .RB ( INADDR_LOOPBACK
255 for IPv4 addresses,
256 .BR IN6ADDR_LOOPBACK_INIT
257 for IPv6 address);
258 this is used by applications that intend to communicate
259 with peers running on the same host.
260 .PP
261 .I service
262 sets the port in each returned address structure.
263 If this argument is a service name (see
264 .BR services (5)),
265 it is translated to the corresponding port number.
266 This argument can also be specified as a decimal number,
267 which is simply converted to binary.
268 If
269 .I service
270 is NULL, then the port number of the returned socket addresses
271 will be left uninitialized.
272 If
273 .B AI_NUMERICSERV
274 is specified in
275 .I hints.ai_flags
276 and
277 .I service
278 is not NULL, then
279 .I service
280 must point to a string containing a numeric port number.
281 This flag is used to inhibit the invocation of a name resolution service
282 in cases where it is known not to be required.
283 .PP
284 Either
285 .I node
286 or
287 .IR service ,
288 but not both, may be NULL.
289 .PP
290 The
291 .BR getaddrinfo ()
292 function allocates and initializes a linked list of
293 .I addrinfo
294 structures, one for each network address that matches
295 .I node
296 and
297 .IR service ,
298 subject to any restrictions imposed by
299 .IR hints ,
300 and returns a pointer to the start of the list in
301 .IR res .
302 The items in the linked list are linked by the
303 .I ai_next
304 field.
305 .PP
306 There are several reasons why
307 the linked list may have more than one
308 .I addrinfo
309 structure, including: the network host is multihomed, accessible
310 over multiple protocols (e.g., both
311 .BR AF_INET
312 and
313 .BR AF_INET6 );
314 or the same service is available from multiple socket types (one
315 .B SOCK_STREAM
316 address and another
317 .B SOCK_DGRAM
318 address, for example).
319 Normally, the application should try
320 using the addresses in the order in which they are returned.
321 The sorting function used within
322 .BR getaddrinfo ()
323 is defined in RFC\ 3484; the order can be tweaked for a particular
324 system by editing
325 .IR /etc/gai.conf
326 (available since glibc 2.5).
327 .PP
328 If
329 .I hints.ai_flags
330 includes the
331 .B AI_CANONNAME
332 flag, then the
333 .I ai_canonname
334 field of the first of the
335 .I addrinfo
336 structures in the returned list is set to point to the
337 official name of the host.
338 .\" In glibc prior to 2.3.4, the ai_canonname of each addrinfo
339 .\" structure was set pointing to the canonical name; that was
340 .\" more than POSIX.1-2001 specified, or other implementations provided.
341 .\" MTK, Aug 05
342 .PP
343 The remaining fields of each returned
344 .I addrinfo
345 structure are initialized as follows:
346 .IP * 2
347 The
348 .IR ai_family ,
349 .IR ai_socktype ,
350 and
351 .I ai_protocol
352 fields return the socket creation parameters (i.e., these fields have
353 the same meaning as the corresponding arguments of
354 .BR socket (2)).
355 For example,
356 .I ai_family
357 might return
358 .B AF_INET
359 or
360 .BR AF_INET6 ;
361 .I ai_socktype
362 might return
363 .B SOCK_DGRAM
364 or
365 .BR SOCK_STREAM ;
366 and
367 .I ai_protocol
368 returns the protocol for the socket.
369 .IP *
370 A pointer to the socket address is placed in the
371 .I ai_addr
372 field, and the length of the socket address, in bytes,
373 is placed in the
374 .I ai_addrlen
375 field.
376 .PP
377 If
378 .I hints.ai_flags
379 includes the
380 .B AI_ADDRCONFIG
381 flag, then IPv4 addresses are returned in the list pointed to by
382 .I res
383 only if the local system has at least one
384 IPv4 address configured, and IPv6 addresses are returned
385 only if the local system has at least one IPv6 address configured.
386 The loopback address is not considered for this case as valid
387 as a configured address.
388 This flag is useful on, for example,
389 IPv4-only systems, to ensure that
390 .BR getaddrinfo ()
391 does not return IPv6 socket addresses that would always fail in
392 .BR connect (2)
393 or
394 .BR bind (2).
395 .PP
396 If
397 .I hints.ai_flags
398 specifies the
399 .B AI_V4MAPPED
400 flag, and
401 .I hints.ai_family
402 was specified as
403 .BR AF_INET6 ,
404 and no matching IPv6 addresses could be found,
405 then return IPv4-mapped IPv6 addresses in the list pointed to by
406 .IR res .
407 If both
408 .B AI_V4MAPPED
409 and
410 .B AI_ALL
411 are specified in
412 .IR hints.ai_flags ,
413 then return both IPv6 and IPv4-mapped IPv6 addresses
414 in the list pointed to by
415 .IR res .
416 .B AI_ALL
417 is ignored if
418 .B AI_V4MAPPED
419 is not also specified.
420 .PP
421 The
422 .BR freeaddrinfo ()
423 function frees the memory that was allocated
424 for the dynamically allocated linked list
425 .IR res .
426 .SS Extensions to getaddrinfo() for Internationalized Domain Names
427 .PP
428 Starting with glibc 2.3.4,
429 .BR getaddrinfo ()
430 has been extended to selectively allow the incoming and outgoing
431 hostnames to be transparently converted to and from the
432 Internationalized Domain Name (IDN) format (see RFC 3490,
433 .IR "Internationalizing Domain Names in Applications (IDNA)" ).
434 Four new flags are defined:
435 .TP
436 .B AI_IDN
437 If this flag is specified, then the node name given in
438 .I node
439 is converted to IDN format if necessary.
440 The source encoding is that of the current locale.
441 .IP
442 If the input name contains non-ASCII characters, then the IDN encoding
443 is used.
444 Those parts of the node name (delimited by dots) that contain
445 non-ASCII characters are encoded using ASCII Compatible Encoding (ACE)
446 before being passed to the name resolution functions.
447 .\" Implementation Detail:
448 .\" To minimize effects on system performance the implementation might
449 .\" want to check whether the input string contains any non-ASCII
450 .\" characters. If there are none the IDN step can be skipped completely.
451 .\" On systems which allow not-ASCII safe encodings for a locale this
452 .\" might be a problem.
453 .TP
454 .B AI_CANONIDN
455 After a successful name lookup, and if the
456 .B AI_CANONNAME
457 flag was specified,
458 .BR getaddrinfo ()
459 will return the canonical name of the
460 node corresponding to the
461 .I addrinfo
462 structure value passed back.
463 The return value is an exact copy of the value returned by the name
464 resolution function.
465 .IP
466 If the name is encoded using ACE, then it will contain the
467 .I xn\-\-
468 prefix for one or more components of the name.
469 To convert these components into a readable form the
470 .B AI_CANONIDN
471 flag can be passed in addition to
472 .BR AI_CANONNAME .
473 The resulting string is encoded using the current locale's encoding.
474 .\"
475 .\"Implementation Detail:
476 .\"If no component of the returned name starts with xn\-\- the IDN
477 .\"step can be skipped, therefore avoiding unnecessary slowdowns.
478 .TP
479 .BR AI_IDN_ALLOW_UNASSIGNED ", " AI_IDN_USE_STD3_ASCII_RULES
480 Setting these flags will enable the
481 IDNA_ALLOW_UNASSIGNED (allow unassigned Unicode code points) and
482 IDNA_USE_STD3_ASCII_RULES (check output to make sure it is a STD3
483 conforming hostname)
484 flags respectively to be used in the IDNA handling.
485 .SH RETURN VALUE
486 .\" FIXME glibc defines the following additional errors, some which
487 .\" can probably be returned by getaddrinfo(); they need to
488 .\" be documented.
489 .\" #ifdef __USE_GNU
490 .\" #define EAI_INPROGRESS -100 /* Processing request in progress. */
491 .\" #define EAI_CANCELED -101 /* Request canceled. */
492 .\" #define EAI_NOTCANCELED -102 /* Request not canceled. */
493 .\" #define EAI_ALLDONE -103 /* All requests done. */
494 .\" #define EAI_INTR -104 /* Interrupted by a signal. */
495 .\" #define EAI_IDN_ENCODE -105 /* IDN encoding failed. */
496 .\" #endif
497 .BR getaddrinfo ()
498 returns 0 if it succeeds, or one of the following nonzero error codes:
499 .TP
500 .B EAI_ADDRFAMILY
501 .\" Not in SUSv3
502 The specified network host does not have any network addresses in the
503 requested address family.
504 .TP
505 .B EAI_AGAIN
506 The name server returned a temporary failure indication.
507 Try again later.
508 .TP
509 .B EAI_BADFLAGS
510 .I hints.ai_flags
511 contains invalid flags; or,
512 .I hints.ai_flags
513 included
514 .B AI_CANONNAME
515 and
516 .I name
517 was NULL.
518 .TP
519 .B EAI_FAIL
520 The name server returned a permanent failure indication.
521 .TP
522 .B EAI_FAMILY
523 The requested address family is not supported.
524 .TP
525 .B EAI_MEMORY
526 Out of memory.
527 .TP
528 .B EAI_NODATA
529 .\" Not in SUSv3
530 The specified network host exists, but does not have any
531 network addresses defined.
532 .TP
533 .B EAI_NONAME
534 The
535 .I node
536 or
537 .I service
538 is not known; or both
539 .I node
540 and
541 .I service
542 are NULL; or
543 .B AI_NUMERICSERV
544 was specified in
545 .I hints.ai_flags
546 and
547 .I service
548 was not a numeric port-number string.
549 .TP
550 .B EAI_SERVICE
551 The requested service is not available for the requested socket type.
552 It may be available through another socket type.
553 For example, this error could occur if
554 .I service
555 was "shell" (a service available only on stream sockets), and either
556 .I hints.ai_protocol
557 was
558 .BR IPPROTO_UDP ,
559 or
560 .I hints.ai_socktype
561 was
562 .BR SOCK_DGRAM ;
563 or the error could occur if
564 .I service
565 was not NULL, and
566 .I hints.ai_socktype
567 was
568 .BR SOCK_RAW
569 (a socket type that does not support the concept of services).
570 .TP
571 .B EAI_SOCKTYPE
572 The requested socket type is not supported.
573 This could occur, for example, if
574 .I hints.ai_socktype
575 and
576 .I hints.ai_protocol
577 are inconsistent (e.g.,
578 .BR SOCK_DGRAM
579 and
580 .BR IPPROTO_TCP ,
581 respectively).
582 .TP
583 .B EAI_SYSTEM
584 Other system error, check
585 .I errno
586 for details.
587 .PP
588 The
589 .BR gai_strerror ()
590 function translates these error codes to a human readable string,
591 suitable for error reporting.
592 .SH FILES
593 .I /etc/gai.conf
594 .SH ATTRIBUTES
595 For an explanation of the terms used in this section, see
596 .BR attributes (7).
597 .TS
598 allbox;
599 lbw15 lb lb
600 l l l.
601 Interface Attribute Value
602 T{
603 .BR getaddrinfo ()
604 T} Thread safety MT-Safe env locale
605 T{
606 .BR freeaddrinfo (),
607 .BR gai_strerror ()
608 T} Thread safety MT-Safe
609 .TE
610 .sp 1
611 .SH CONFORMING TO
612 POSIX.1-2001, POSIX.1-2008.
613 The
614 .BR getaddrinfo ()
615 function is documented in RFC\ 2553.
616 .SH NOTES
617 .BR getaddrinfo ()
618 supports the
619 .IB address % scope-id
620 notation for specifying the IPv6 scope-ID.
621 .PP
622 .BR AI_ADDRCONFIG ,
623 .BR AI_ALL ,
624 and
625 .B AI_V4MAPPED
626 are available since glibc 2.3.3.
627 .B AI_NUMERICSERV
628 is available since glibc 2.3.4.
629 .PP
630 According to POSIX.1, specifying
631 .\" POSIX.1-2001, POSIX.1-2008
632 .I hints
633 as NULL should cause
634 .I ai_flags
635 to be assumed as 0.
636 The GNU C library instead assumes a value of
637 .BR "(AI_V4MAPPED\ |\ AI_ADDRCONFIG)"
638 for this case,
639 since this value is considered an improvement on the specification.
640 .SH EXAMPLE
641 .\" getnameinfo.3 refers to this example
642 .\" socket.2 refers to this example
643 .\" bind.2 refers to this example
644 .\" connect.2 refers to this example
645 .\" recvfrom.2 refers to this example
646 .\" sendto.2 refers to this example
647 The following programs demonstrate the use of
648 .BR getaddrinfo (),
649 .BR gai_strerror (),
650 .BR freeaddrinfo (),
651 and
652 .BR getnameinfo (3).
653 The programs are an echo server and client for UDP datagrams.
654 .SS Server program
655 \&
656 .EX
657 #include <sys/types.h>
658 #include <stdio.h>
659 #include <stdlib.h>
660 #include <unistd.h>
661 #include <string.h>
662 #include <sys/socket.h>
663 #include <netdb.h>
665 #define BUF_SIZE 500
667 int
668 main(int argc, char *argv[])
669 {
670 struct addrinfo hints;
671 struct addrinfo *result, *rp;
672 int sfd, s;
673 struct sockaddr_storage peer_addr;
674 socklen_t peer_addr_len;
675 ssize_t nread;
676 char buf[BUF_SIZE];
678 if (argc != 2) {
679 fprintf(stderr, "Usage: %s port\en", argv[0]);
680 exit(EXIT_FAILURE);
681 }
683 memset(&hints, 0, sizeof(struct addrinfo));
684 hints.ai_family = AF_UNSPEC; /* Allow IPv4 or IPv6 */
685 hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
686 hints.ai_flags = AI_PASSIVE; /* For wildcard IP address */
687 hints.ai_protocol = 0; /* Any protocol */
688 hints.ai_canonname = NULL;
689 hints.ai_addr = NULL;
690 hints.ai_next = NULL;
692 s = getaddrinfo(NULL, argv[1], &hints, &result);
693 if (s != 0) {
694 fprintf(stderr, "getaddrinfo: %s\en", gai_strerror(s));
695 exit(EXIT_FAILURE);
696 }
698 /* getaddrinfo() returns a list of address structures.
699 Try each address until we successfully bind(2).
700 If socket(2) (or bind(2)) fails, we (close the socket
701 and) try the next address. */
703 for (rp = result; rp != NULL; rp = rp\->ai_next) {
704 sfd = socket(rp\->ai_family, rp\->ai_socktype,
705 rp\->ai_protocol);
706 if (sfd == \-1)
707 continue;
709 if (bind(sfd, rp\->ai_addr, rp\->ai_addrlen) == 0)
710 break; /* Success */
712 close(sfd);
713 }
715 if (rp == NULL) { /* No address succeeded */
716 fprintf(stderr, "Could not bind\en");
717 exit(EXIT_FAILURE);
718 }
720 freeaddrinfo(result); /* No longer needed */
722 /* Read datagrams and echo them back to sender */
724 for (;;) {
725 peer_addr_len = sizeof(struct sockaddr_storage);
726 nread = recvfrom(sfd, buf, BUF_SIZE, 0,
727 (struct sockaddr *) &peer_addr, &peer_addr_len);
728 if (nread == \-1)
729 continue; /* Ignore failed request */
731 char host[NI_MAXHOST], service[NI_MAXSERV];
733 s = getnameinfo((struct sockaddr *) &peer_addr,
734 peer_addr_len, host, NI_MAXHOST,
735 service, NI_MAXSERV, NI_NUMERICSERV);
736 if (s == 0)
737 printf("Received %zd bytes from %s:%s\en",
738 nread, host, service);
739 else
740 fprintf(stderr, "getnameinfo: %s\en", gai_strerror(s));
742 if (sendto(sfd, buf, nread, 0,
743 (struct sockaddr *) &peer_addr,
744 peer_addr_len) != nread)
745 fprintf(stderr, "Error sending response\en");
746 }
747 }
748 .EE
749 .SS Client program
750 \&
751 .EX
752 #include <sys/types.h>
753 #include <sys/socket.h>
754 #include <netdb.h>
755 #include <stdio.h>
756 #include <stdlib.h>
757 #include <unistd.h>
758 #include <string.h>
760 #define BUF_SIZE 500
762 int
763 main(int argc, char *argv[])
764 {
765 struct addrinfo hints;
766 struct addrinfo *result, *rp;
767 int sfd, s, j;
768 size_t len;
769 ssize_t nread;
770 char buf[BUF_SIZE];
772 if (argc < 3) {
773 fprintf(stderr, "Usage: %s host port msg...\en", argv[0]);
774 exit(EXIT_FAILURE);
775 }
777 /* Obtain address(es) matching host/port */
779 memset(&hints, 0, sizeof(struct addrinfo));
780 hints.ai_family = AF_UNSPEC; /* Allow IPv4 or IPv6 */
781 hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
782 hints.ai_flags = 0;
783 hints.ai_protocol = 0; /* Any protocol */
785 s = getaddrinfo(argv[1], argv[2], &hints, &result);
786 if (s != 0) {
787 fprintf(stderr, "getaddrinfo: %s\en", gai_strerror(s));
788 exit(EXIT_FAILURE);
789 }
791 /* getaddrinfo() returns a list of address structures.
792 Try each address until we successfully connect(2).
793 If socket(2) (or connect(2)) fails, we (close the socket
794 and) try the next address. */
796 for (rp = result; rp != NULL; rp = rp\->ai_next) {
797 sfd = socket(rp\->ai_family, rp\->ai_socktype,
798 rp\->ai_protocol);
799 if (sfd == \-1)
800 continue;
802 if (connect(sfd, rp\->ai_addr, rp\->ai_addrlen) != \-1)
803 break; /* Success */
805 close(sfd);
806 }
808 if (rp == NULL) { /* No address succeeded */
809 fprintf(stderr, "Could not connect\en");
810 exit(EXIT_FAILURE);
811 }
813 freeaddrinfo(result); /* No longer needed */
815 /* Send remaining command\-line arguments as separate
816 datagrams, and read responses from server */
818 for (j = 3; j < argc; j++) {
819 len = strlen(argv[j]) + 1;
820 /* +1 for terminating null byte */
822 if (len > BUF_SIZE) {
823 fprintf(stderr,
824 "Ignoring long message in argument %d\en", j);
825 continue;
826 }
828 if (write(sfd, argv[j], len) != len) {
829 fprintf(stderr, "partial/failed write\en");
830 exit(EXIT_FAILURE);
831 }
833 nread = read(sfd, buf, BUF_SIZE);
834 if (nread == \-1) {
835 perror("read");
836 exit(EXIT_FAILURE);
837 }
839 printf("Received %zd bytes: %s\en", nread, buf);
840 }
842 exit(EXIT_SUCCESS);
843 }
844 .EE
845 .SH SEE ALSO
846 .\" .BR getipnodebyaddr (3),
847 .\" .BR getipnodebyname (3),
848 .BR getaddrinfo_a (3),
849 .BR gethostbyname (3),
850 .BR getnameinfo (3),
851 .BR inet (3),
852 .BR gai.conf (5),
853 .BR hostname (7),
854 .BR ip (7)