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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17 .\" manual page may be incorrect or out-of-date.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 2021-08-27 "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 *restrict " node ,
55 .BI " const char *restrict " service ,
56 .BI " const struct addrinfo *restrict " hints ,
57 .BI " struct addrinfo **restrict " res );
58 .PP
59 .BI "void freeaddrinfo(struct addrinfo *" res );
60 .PP
61 .BI "const char *gai_strerror(int " errcode );
62 .fi
63 .PP
64 .RS -4
65 Feature Test Macro Requirements for glibc (see
66 .BR feature_test_macros (7)):
67 .RE
68 .PP
69 .BR getaddrinfo (),
70 .BR freeaddrinfo (),
71 .BR gai_strerror ():
72 .nf
73 Since glibc 2.22:
74 _POSIX_C_SOURCE >= 200112L
75 Glibc 2.21 and earlier:
76 _POSIX_C_SOURCE
77 .fi
78 .SH DESCRIPTION
79 Given
80 .I node
81 and
82 .IR service ,
83 which identify an Internet host and a service,
84 .BR getaddrinfo ()
85 returns one or more
86 .I addrinfo
87 structures, each of which contains an Internet address
88 that can be specified in a call to
89 .BR bind (2)
90 or
91 .BR connect (2).
92 The
93 .BR getaddrinfo ()
94 function combines the functionality provided by the
95 .\" .BR getipnodebyname (3),
96 .\" .BR getipnodebyaddr (3),
97 .BR gethostbyname (3)
98 and
99 .BR getservbyname (3)
100 functions into a single interface, but unlike the latter functions,
101 .BR getaddrinfo ()
102 is reentrant and allows programs to eliminate IPv4-versus-IPv6 dependencies.
103 .PP
104 The
105 .I addrinfo
106 structure used by
107 .BR getaddrinfo ()
108 contains the following fields:
109 .PP
110 .in +4n
111 .EX
112 struct addrinfo {
113 int ai_flags;
114 int ai_family;
115 int ai_socktype;
116 int ai_protocol;
117 socklen_t ai_addrlen;
118 struct sockaddr *ai_addr;
119 char *ai_canonname;
120 struct addrinfo *ai_next;
121 };
122 .EE
123 .in
124 .PP
125 The
126 .I hints
127 argument points to an
128 .I addrinfo
129 structure that specifies criteria for selecting the socket address
130 structures returned in the list pointed to by
131 .IR res .
132 If
133 .I hints
134 is not NULL it points to an
135 .I addrinfo
136 structure whose
137 .IR ai_family ,
138 .IR ai_socktype ,
139 and
140 .I ai_protocol
141 specify criteria that limit the set of socket addresses returned by
142 .BR getaddrinfo (),
143 as follows:
144 .TP
145 .I ai_family
146 This field specifies the desired address family for the returned addresses.
147 Valid values for this field include
148 .BR AF_INET
149 and
150 .BR AF_INET6 .
151 The value
152 .B AF_UNSPEC
153 indicates that
154 .BR getaddrinfo ()
155 should return socket addresses for any address family
156 (either IPv4 or IPv6, for example) that can be used with
157 .I node
158 and
159 .IR service .
160 .TP
161 .I ai_socktype
162 This field specifies the preferred socket type, for example
163 .BR SOCK_STREAM
164 or
165 .BR SOCK_DGRAM .
166 Specifying 0 in this field indicates that socket addresses of any type
167 can be returned by
168 .BR getaddrinfo ().
169 .TP
170 .I ai_protocol
171 This field specifies the protocol for the returned socket addresses.
172 Specifying 0 in this field indicates that socket addresses with
173 any protocol can be returned by
174 .BR getaddrinfo ().
175 .TP
176 .I ai_flags
177 This field specifies additional options, described below.
178 Multiple flags are specified by bitwise OR-ing them together.
179 .PP
180 All the other fields in the structure pointed to by
181 .I hints
182 must contain either 0 or a null pointer, as appropriate.
183 .PP
184 Specifying
185 .I hints
186 as NULL is equivalent to setting
187 .I ai_socktype
188 and
189 .I ai_protocol
190 to 0;
191 .I ai_family
192 to
193 .BR AF_UNSPEC ;
194 and
195 .I ai_flags
196 to
197 .BR "(AI_V4MAPPED\ |\ AI_ADDRCONFIG)" .
198 (POSIX specifies different defaults for
199 .IR ai_flags ;
200 see NOTES.)
201 .I node
202 specifies either a numerical network address
203 (for IPv4, numbers-and-dots notation as supported by
204 .BR inet_aton (3);
205 for IPv6, hexadecimal string format as supported by
206 .BR inet_pton (3)),
207 or a network hostname, whose network addresses are looked up and resolved.
208 If
209 .I hints.ai_flags
210 contains the
211 .B AI_NUMERICHOST
212 flag, then
213 .I node
214 must be a numerical network address.
215 The
216 .B AI_NUMERICHOST
217 flag suppresses any potentially lengthy network host address lookups.
218 .PP
219 If the
220 .B AI_PASSIVE
221 flag is specified in
222 .IR hints.ai_flags ,
223 and
224 .I node
225 is NULL,
226 then the returned socket addresses will be suitable for
227 .BR bind (2)ing
228 a socket that will
229 .BR accept (2)
230 connections.
231 The returned socket address will contain the "wildcard address"
232 .RB ( INADDR_ANY
233 for IPv4 addresses,
234 .BR IN6ADDR_ANY_INIT
235 for IPv6 address).
236 The wildcard address is used by applications (typically servers)
237 that intend to accept connections on any of the host's network addresses.
238 If
239 .I node
240 is not NULL, then the
241 .B AI_PASSIVE
242 flag is ignored.
243 .PP
244 If the
245 .B AI_PASSIVE
246 flag is not set in
247 .IR hints.ai_flags ,
248 then the returned socket addresses will be suitable for use with
249 .BR connect (2),
250 .BR sendto (2),
251 or
252 .BR sendmsg (2).
253 If
254 .I node
255 is NULL,
256 then the network address will be set to the loopback interface address
257 .RB ( INADDR_LOOPBACK
258 for IPv4 addresses,
259 .BR IN6ADDR_LOOPBACK_INIT
260 for IPv6 address);
261 this is used by applications that intend to communicate
262 with peers running on the same host.
263 .PP
264 .I service
265 sets the port in each returned address structure.
266 If this argument is a service name (see
267 .BR services (5)),
268 it is translated to the corresponding port number.
269 This argument can also be specified as a decimal number,
270 which is simply converted to binary.
271 If
272 .I service
273 is NULL, then the port number of the returned socket addresses
274 will be left uninitialized.
275 If
276 .B AI_NUMERICSERV
277 is specified in
278 .I hints.ai_flags
279 and
280 .I service
281 is not NULL, then
282 .I service
283 must point to a string containing a numeric port number.
284 This flag is used to inhibit the invocation of a name resolution service
285 in cases where it is known not to be required.
286 .PP
287 Either
288 .I node
289 or
290 .IR service ,
291 but not both, may be NULL.
292 .PP
293 The
294 .BR getaddrinfo ()
295 function allocates and initializes a linked list of
296 .I addrinfo
297 structures, one for each network address that matches
298 .I node
299 and
300 .IR service ,
301 subject to any restrictions imposed by
302 .IR hints ,
303 and returns a pointer to the start of the list in
304 .IR res .
305 The items in the linked list are linked by the
306 .I ai_next
307 field.
308 .PP
309 There are several reasons why
310 the linked list may have more than one
311 .I addrinfo
312 structure, including: the network host is multihomed, accessible
313 over multiple protocols (e.g., both
314 .BR AF_INET
315 and
316 .BR AF_INET6 );
317 or the same service is available from multiple socket types (one
318 .B SOCK_STREAM
319 address and another
320 .B SOCK_DGRAM
321 address, for example).
322 Normally, the application should try
323 using the addresses in the order in which they are returned.
324 The sorting function used within
325 .BR getaddrinfo ()
326 is defined in RFC\ 3484; the order can be tweaked for a particular
327 system by editing
328 .IR /etc/gai.conf
329 (available since glibc 2.5).
330 .PP
331 If
332 .I hints.ai_flags
333 includes the
334 .B AI_CANONNAME
335 flag, then the
336 .I ai_canonname
337 field of the first of the
338 .I addrinfo
339 structures in the returned list is set to point to the
340 official name of the host.
341 .\" In glibc prior to 2.3.4, the ai_canonname of each addrinfo
342 .\" structure was set pointing to the canonical name; that was
343 .\" more than POSIX.1-2001 specified, or other implementations provided.
344 .\" MTK, Aug 05
345 .PP
346 The remaining fields of each returned
347 .I addrinfo
348 structure are initialized as follows:
349 .IP * 2
350 The
351 .IR ai_family ,
352 .IR ai_socktype ,
353 and
354 .I ai_protocol
355 fields return the socket creation parameters (i.e., these fields have
356 the same meaning as the corresponding arguments of
357 .BR socket (2)).
358 For example,
359 .I ai_family
360 might return
361 .B AF_INET
362 or
363 .BR AF_INET6 ;
364 .I ai_socktype
365 might return
366 .B SOCK_DGRAM
367 or
368 .BR SOCK_STREAM ;
369 and
370 .I ai_protocol
371 returns the protocol for the socket.
372 .IP *
373 A pointer to the socket address is placed in the
374 .I ai_addr
375 field, and the length of the socket address, in bytes,
376 is placed in the
377 .I ai_addrlen
378 field.
379 .PP
380 If
381 .I hints.ai_flags
382 includes the
383 .B AI_ADDRCONFIG
384 flag, then IPv4 addresses are returned in the list pointed to by
385 .I res
386 only if the local system has at least one
387 IPv4 address configured, and IPv6 addresses are returned
388 only if the local system has at least one IPv6 address configured.
389 The loopback address is not considered for this case as valid
390 as a configured address.
391 This flag is useful on, for example,
392 IPv4-only systems, to ensure that
393 .BR getaddrinfo ()
394 does not return IPv6 socket addresses that would always fail in
395 .BR connect (2)
396 or
397 .BR bind (2).
398 .PP
399 If
400 .I hints.ai_flags
401 specifies the
402 .B AI_V4MAPPED
403 flag, and
404 .I hints.ai_family
405 was specified as
406 .BR AF_INET6 ,
407 and no matching IPv6 addresses could be found,
408 then return IPv4-mapped IPv6 addresses in the list pointed to by
409 .IR res .
410 If both
411 .B AI_V4MAPPED
412 and
413 .B AI_ALL
414 are specified in
415 .IR hints.ai_flags ,
416 then return both IPv6 and IPv4-mapped IPv6 addresses
417 in the list pointed to by
418 .IR res .
419 .B AI_ALL
420 is ignored if
421 .B AI_V4MAPPED
422 is not also specified.
423 .PP
424 The
425 .BR freeaddrinfo ()
426 function frees the memory that was allocated
427 for the dynamically allocated linked list
428 .IR res .
429 .SS Extensions to getaddrinfo() for Internationalized Domain Names
430 Starting with glibc 2.3.4,
431 .BR getaddrinfo ()
432 has been extended to selectively allow the incoming and outgoing
433 hostnames to be transparently converted to and from the
434 Internationalized Domain Name (IDN) format (see RFC 3490,
435 .IR "Internationalizing Domain Names in Applications (IDNA)" ).
436 Four new flags are defined:
437 .TP
438 .B AI_IDN
439 If this flag is specified, then the node name given in
440 .I node
441 is converted to IDN format if necessary.
442 The source encoding is that of the current locale.
443 .IP
444 If the input name contains non-ASCII characters, then the IDN encoding
445 is used.
446 Those parts of the node name (delimited by dots) that contain
447 non-ASCII characters are encoded using ASCII Compatible Encoding (ACE)
448 before being passed to the name resolution functions.
449 .\" Implementation Detail:
450 .\" To minimize effects on system performance the implementation might
451 .\" want to check whether the input string contains any non-ASCII
452 .\" characters. If there are none the IDN step can be skipped completely.
453 .\" On systems which allow not-ASCII safe encodings for a locale this
454 .\" might be a problem.
455 .TP
456 .B AI_CANONIDN
457 After a successful name lookup, and if the
458 .B AI_CANONNAME
459 flag was specified,
460 .BR getaddrinfo ()
461 will return the canonical name of the
462 node corresponding to the
463 .I addrinfo
464 structure value passed back.
465 The return value is an exact copy of the value returned by the name
466 resolution function.
467 .IP
468 If the name is encoded using ACE, then it will contain the
469 .I xn\-\-
470 prefix for one or more components of the name.
471 To convert these components into a readable form the
472 .B AI_CANONIDN
473 flag can be passed in addition to
474 .BR AI_CANONNAME .
475 The resulting string is encoded using the current locale's encoding.
476 .\"
477 .\"Implementation Detail:
478 .\"If no component of the returned name starts with xn\-\- the IDN
479 .\"step can be skipped, therefore avoiding unnecessary slowdowns.
480 .TP
481 .BR AI_IDN_ALLOW_UNASSIGNED ", " AI_IDN_USE_STD3_ASCII_RULES
482 Setting these flags will enable the
483 IDNA_ALLOW_UNASSIGNED (allow unassigned Unicode code points) and
484 IDNA_USE_STD3_ASCII_RULES (check output to make sure it is a STD3
485 conforming hostname)
486 flags respectively to be used in the IDNA handling.
487 .SH RETURN VALUE
488 .\" FIXME glibc defines the following additional errors, some which
489 .\" can probably be returned by getaddrinfo(); they need to
490 .\" be documented.
491 .\" #ifdef __USE_GNU
492 .\" #define EAI_INPROGRESS -100 /* Processing request in progress. */
493 .\" #define EAI_CANCELED -101 /* Request canceled. */
494 .\" #define EAI_NOTCANCELED -102 /* Request not canceled. */
495 .\" #define EAI_ALLDONE -103 /* All requests done. */
496 .\" #define EAI_INTR -104 /* Interrupted by a signal. */
497 .\" #define EAI_IDN_ENCODE -105 /* IDN encoding failed. */
498 .\" #endif
499 .BR getaddrinfo ()
500 returns 0 if it succeeds, or one of the following nonzero error codes:
501 .TP
502 .B EAI_ADDRFAMILY
503 .\" Not in SUSv3
504 The specified network host does not have any network addresses in the
505 requested address family.
506 .TP
507 .B EAI_AGAIN
508 The name server returned a temporary failure indication.
509 Try again later.
510 .TP
511 .B EAI_BADFLAGS
512 .I hints.ai_flags
513 contains invalid flags; or,
514 .I hints.ai_flags
515 included
516 .B AI_CANONNAME
517 and
518 .I name
519 was NULL.
520 .TP
521 .B EAI_FAIL
522 The name server returned a permanent failure indication.
523 .TP
524 .B EAI_FAMILY
525 The requested address family is not supported.
526 .TP
527 .B EAI_MEMORY
528 Out of memory.
529 .TP
530 .B EAI_NODATA
531 .\" Not in SUSv3
532 The specified network host exists, but does not have any
533 network addresses defined.
534 .TP
535 .B EAI_NONAME
536 The
537 .I node
538 or
539 .I service
540 is not known; or both
541 .I node
542 and
543 .I service
544 are NULL; or
545 .B AI_NUMERICSERV
546 was specified in
547 .I hints.ai_flags
548 and
549 .I service
550 was not a numeric port-number string.
551 .TP
552 .B EAI_SERVICE
553 The requested service is not available for the requested socket type.
554 It may be available through another socket type.
555 For example, this error could occur if
556 .I service
557 was "shell" (a service available only on stream sockets), and either
558 .I hints.ai_protocol
559 was
560 .BR IPPROTO_UDP ,
561 or
562 .I hints.ai_socktype
563 was
564 .BR SOCK_DGRAM ;
565 or the error could occur if
566 .I service
567 was not NULL, and
568 .I hints.ai_socktype
569 was
570 .BR SOCK_RAW
571 (a socket type that does not support the concept of services).
572 .TP
573 .B EAI_SOCKTYPE
574 The requested socket type is not supported.
575 This could occur, for example, if
576 .I hints.ai_socktype
577 and
578 .I hints.ai_protocol
579 are inconsistent (e.g.,
580 .BR SOCK_DGRAM
581 and
582 .BR IPPROTO_TCP ,
583 respectively).
584 .TP
585 .B EAI_SYSTEM
586 Other system error;
587 .I errno
588 is set to indicate the error.
589 .PP
590 The
591 .BR gai_strerror ()
592 function translates these error codes to a human readable string,
593 suitable for error reporting.
594 .SH FILES
595 .I /etc/gai.conf
596 .SH ATTRIBUTES
597 For an explanation of the terms used in this section, see
598 .BR attributes (7).
599 .ad l
600 .nh
601 .TS
602 allbox;
603 lbx lb lb
604 l l l.
605 Interface Attribute Value
606 T{
607 .BR getaddrinfo ()
608 T} Thread safety MT-Safe env locale
609 T{
610 .BR freeaddrinfo (),
611 .BR gai_strerror ()
612 T} Thread safety MT-Safe
613 .TE
614 .hy
615 .ad
616 .sp 1
617 .SH CONFORMING TO
618 POSIX.1-2001, POSIX.1-2008.
619 The
620 .BR getaddrinfo ()
621 function is documented in RFC\ 2553.
622 .SH NOTES
623 .BR getaddrinfo ()
624 supports the
625 .IB address % scope-id
626 notation for specifying the IPv6 scope-ID.
627 .PP
628 .BR AI_ADDRCONFIG ,
629 .BR AI_ALL ,
630 and
631 .B AI_V4MAPPED
632 are available since glibc 2.3.3.
633 .B AI_NUMERICSERV
634 is available since glibc 2.3.4.
635 .PP
636 According to POSIX.1, specifying
637 .\" POSIX.1-2001, POSIX.1-2008
638 .I hints
639 as NULL should cause
640 .I ai_flags
641 to be assumed as 0.
642 The GNU C library instead assumes a value of
643 .BR "(AI_V4MAPPED\ |\ AI_ADDRCONFIG)"
644 for this case,
645 since this value is considered an improvement on the specification.
646 .SH EXAMPLES
647 .\" getnameinfo.3 refers to this example
648 .\" socket.2 refers to this example
649 .\" bind.2 refers to this example
650 .\" connect.2 refers to this example
651 .\" recvfrom.2 refers to this example
652 .\" sendto.2 refers to this example
653 The following programs demonstrate the use of
654 .BR getaddrinfo (),
655 .BR gai_strerror (),
656 .BR freeaddrinfo (),
657 and
658 .BR getnameinfo (3).
659 The programs are an echo server and client for UDP datagrams.
660 .SS Server program
661 \&
662 .EX
663 #include <sys/types.h>
664 #include <stdio.h>
665 #include <stdlib.h>
666 #include <unistd.h>
667 #include <string.h>
668 #include <sys/socket.h>
669 #include <netdb.h>
671 #define BUF_SIZE 500
673 int
674 main(int argc, char *argv[])
675 {
676 struct addrinfo hints;
677 struct addrinfo *result, *rp;
678 int sfd, s;
679 struct sockaddr_storage peer_addr;
680 socklen_t peer_addr_len;
681 ssize_t nread;
682 char buf[BUF_SIZE];
684 if (argc != 2) {
685 fprintf(stderr, "Usage: %s port\en", argv[0]);
686 exit(EXIT_FAILURE);
687 }
689 memset(&hints, 0, sizeof(hints));
690 hints.ai_family = AF_UNSPEC; /* Allow IPv4 or IPv6 */
691 hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
692 hints.ai_flags = AI_PASSIVE; /* For wildcard IP address */
693 hints.ai_protocol = 0; /* Any protocol */
694 hints.ai_canonname = NULL;
695 hints.ai_addr = NULL;
696 hints.ai_next = NULL;
698 s = getaddrinfo(NULL, argv[1], &hints, &result);
699 if (s != 0) {
700 fprintf(stderr, "getaddrinfo: %s\en", gai_strerror(s));
701 exit(EXIT_FAILURE);
702 }
704 /* getaddrinfo() returns a list of address structures.
705 Try each address until we successfully bind(2).
706 If socket(2) (or bind(2)) fails, we (close the socket
707 and) try the next address. */
709 for (rp = result; rp != NULL; rp = rp\->ai_next) {
710 sfd = socket(rp\->ai_family, rp\->ai_socktype,
711 rp\->ai_protocol);
712 if (sfd == \-1)
713 continue;
715 if (bind(sfd, rp\->ai_addr, rp\->ai_addrlen) == 0)
716 break; /* Success */
718 close(sfd);
719 }
721 freeaddrinfo(result); /* No longer needed */
723 if (rp == NULL) { /* No address succeeded */
724 fprintf(stderr, "Could not bind\en");
725 exit(EXIT_FAILURE);
726 }
728 /* Read datagrams and echo them back to sender. */
730 for (;;) {
731 peer_addr_len = sizeof(peer_addr);
732 nread = recvfrom(sfd, buf, BUF_SIZE, 0,
733 (struct sockaddr *) &peer_addr, &peer_addr_len);
734 if (nread == \-1)
735 continue; /* Ignore failed request */
737 char host[NI_MAXHOST], service[NI_MAXSERV];
739 s = getnameinfo((struct sockaddr *) &peer_addr,
740 peer_addr_len, host, NI_MAXHOST,
741 service, NI_MAXSERV, NI_NUMERICSERV);
742 if (s == 0)
743 printf("Received %zd bytes from %s:%s\en",
744 nread, host, service);
745 else
746 fprintf(stderr, "getnameinfo: %s\en", gai_strerror(s));
748 if (sendto(sfd, buf, nread, 0,
749 (struct sockaddr *) &peer_addr,
750 peer_addr_len) != nread)
751 fprintf(stderr, "Error sending response\en");
752 }
753 }
754 .EE
755 .SS Client program
756 \&
757 .EX
758 #include <sys/types.h>
759 #include <sys/socket.h>
760 #include <netdb.h>
761 #include <stdio.h>
762 #include <stdlib.h>
763 #include <unistd.h>
764 #include <string.h>
766 #define BUF_SIZE 500
768 int
769 main(int argc, char *argv[])
770 {
771 struct addrinfo hints;
772 struct addrinfo *result, *rp;
773 int sfd, s;
774 size_t len;
775 ssize_t nread;
776 char buf[BUF_SIZE];
778 if (argc < 3) {
779 fprintf(stderr, "Usage: %s host port msg...\en", argv[0]);
780 exit(EXIT_FAILURE);
781 }
783 /* Obtain address(es) matching host/port. */
785 memset(&hints, 0, sizeof(hints));
786 hints.ai_family = AF_UNSPEC; /* Allow IPv4 or IPv6 */
787 hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
788 hints.ai_flags = 0;
789 hints.ai_protocol = 0; /* Any protocol */
791 s = getaddrinfo(argv[1], argv[2], &hints, &result);
792 if (s != 0) {
793 fprintf(stderr, "getaddrinfo: %s\en", gai_strerror(s));
794 exit(EXIT_FAILURE);
795 }
797 /* getaddrinfo() returns a list of address structures.
798 Try each address until we successfully connect(2).
799 If socket(2) (or connect(2)) fails, we (close the socket
800 and) try the next address. */
802 for (rp = result; rp != NULL; rp = rp\->ai_next) {
803 sfd = socket(rp\->ai_family, rp\->ai_socktype,
804 rp\->ai_protocol);
805 if (sfd == \-1)
806 continue;
808 if (connect(sfd, rp\->ai_addr, rp\->ai_addrlen) != \-1)
809 break; /* Success */
811 close(sfd);
812 }
814 freeaddrinfo(result); /* No longer needed */
816 if (rp == NULL) { /* No address succeeded */
817 fprintf(stderr, "Could not connect\en");
818 exit(EXIT_FAILURE);
819 }
821 /* Send remaining command\-line arguments as separate
822 datagrams, and read responses from server. */
824 for (int j = 3; j < argc; j++) {
825 len = strlen(argv[j]) + 1;
826 /* +1 for terminating null byte */
828 if (len > BUF_SIZE) {
829 fprintf(stderr,
830 "Ignoring long message in argument %d\en", j);
831 continue;
832 }
834 if (write(sfd, argv[j], len) != len) {
835 fprintf(stderr, "partial/failed write\en");
836 exit(EXIT_FAILURE);
837 }
839 nread = read(sfd, buf, BUF_SIZE);
840 if (nread == \-1) {
841 perror("read");
842 exit(EXIT_FAILURE);
843 }
845 printf("Received %zd bytes: %s\en", nread, buf);
846 }
848 exit(EXIT_SUCCESS);
849 }
850 .EE
851 .SH SEE ALSO
852 .\" .BR getipnodebyaddr (3),
853 .\" .BR getipnodebyname (3),
854 .BR getaddrinfo_a (3),
855 .BR gethostbyname (3),
856 .BR getnameinfo (3),
857 .BR inet (3),
858 .BR gai.conf (5),
859 .BR hostname (7),
860 .BR ip (7)