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1 .\" $KAME: getaddrinfo.3,v 1.36 2005/01/05 03:23:05 itojun Exp $
2 .\" $OpenBSD: getaddrinfo.3,v 1.35 2004/12/21 03:40:31 jaredy Exp $
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5 .\" Copyright (C) 2000, 2001 Internet Software Consortium.
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19 .\" $FreeBSD: src/lib/libc/net/getaddrinfo.3,v 1.36 2009/01/06 13:10:15 danger Exp $
20 .\"
21 .Dd February 22, 2018
22 .Dt GETADDRINFO 3
23 .Os
24 .Sh NAME
25 .Nm getaddrinfo ,
26 .Nm freeaddrinfo
27 .Nd socket address structure to host and service name
28 .Sh LIBRARY
29 .Lb libc
30 .Sh SYNOPSIS
31 .In sys/types.h
32 .In sys/socket.h
33 .In netdb.h
34 .Ft int
35 .Fo getaddrinfo
36 .Fa "const char * restrict hostname" "const char * restrict servname"
37 .Fa "const struct addrinfo * restrict hints" "struct addrinfo ** restrict res"
38 .Fc
39 .Ft void
40 .Fn freeaddrinfo "struct addrinfo *ai"
41 .Sh DESCRIPTION
42 The
43 .Fn getaddrinfo
44 function is used to get a list of
45 .Tn IP
46 addresses and port numbers for host
47 .Fa hostname
48 and service
49 .Fa servname .
50 It is a replacement for and provides more flexibility than the
51 .Xr gethostbyname 3
52 and
53 .Xr getservbyname 3
54 functions.
55 .Pp
56 The
57 .Fa hostname
58 and
59 .Fa servname
60 arguments are either pointers to NUL-terminated strings or the null pointer.
61 An acceptable value for
62 .Fa hostname
63 is either a valid host name or a numeric host address string consisting
64 of a dotted decimal IPv4 address or an IPv6 address.
65 The
66 .Fa servname
67 is either a decimal port number or a service name listed in
68 .Xr services 5 .
69 At least one of
70 .Fa hostname
71 and
72 .Fa servname
73 must be non-null.
74 .Pp
75 .Fa hints
76 is an optional pointer to a
77 .Li struct addrinfo ,
78 as defined by
79 .In netdb.h :
80 .Bd -literal
81 struct addrinfo {
82 int ai_flags; /* input flags */
83 int ai_family; /* protocol family for socket */
84 int ai_socktype; /* socket type */
85 int ai_protocol; /* protocol for socket */
86 socklen_t ai_addrlen; /* length of socket-address */
87 struct sockaddr *ai_addr; /* socket-address for socket */
88 char *ai_canonname; /* canonical name for service location */
89 struct addrinfo *ai_next; /* pointer to next in list */
90 };
91 .Ed
92 .Pp
93 This structure can be used to provide hints concerning the type of socket
94 that the caller supports or wishes to use.
95 The caller can supply the following structure elements in
96 .Fa hints :
97 .Bl -tag -width "ai_socktypeXX"
98 .It Fa ai_family
99 The protocol family that should be used.
100 When
101 .Fa ai_family
102 is set to
103 .Dv PF_UNSPEC ,
104 it means the caller will accept any protocol family supported by the
105 operating system.
106 .It Fa ai_socktype
107 Denotes the type of socket that is wanted:
108 .Dv SOCK_STREAM ,
109 .Dv SOCK_DGRAM ,
110 or
111 .Dv SOCK_RAW .
112 When
113 .Fa ai_socktype
114 is zero the caller will accept any socket type.
115 .It Fa ai_protocol
116 Indicates which transport protocol is desired,
117 .Dv IPPROTO_UDP
118 or
119 .Dv IPPROTO_TCP .
120 If
121 .Fa ai_protocol
122 is zero the caller will accept any protocol.
123 .It Fa ai_flags
124 The
125 .Fa ai_flags
126 field to which the
127 .Fa hints
128 parameter points shall be set to zero
129 or be the bitwise-inclusive OR of one or more of the values
130 .Dv AI_ADDRCONFIG ,
131 .Dv AI_CANONNAME ,
132 .Dv AI_NUMERICHOST ,
133 .Dv AI_NUMERICSERV
134 and
135 .Dv AI_PASSIVE .
136 .Bl -tag -width "AI_CANONNAMEXX"
137 .It Dv AI_ADDRCONFIG
138 If the
139 .Dv AI_ADDRCONFIG
140 bit is set, IPv4 addresses shall be returned only if
141 an IPv4 address is configured on the local system,
142 and IPv6 addresses shall be returned only if
143 an IPv6 address is configured on the local system.
144 .It Dv AI_CANONNAME
145 If the
146 .Dv AI_CANONNAME
147 bit is set, a successful call to
148 .Fn getaddrinfo
149 will return a NUL-terminated string containing the canonical name
150 of the specified hostname in the
151 .Fa ai_canonname
152 element of the first
153 .Li addrinfo
154 structure returned.
155 .It Dv AI_NUMERICHOST
156 If the
157 .Dv AI_NUMERICHOST
158 bit is set, it indicates that
159 .Fa hostname
160 should be treated as a numeric string defining an IPv4 or IPv6 address
161 and no name resolution should be attempted.
162 .It Dv AI_NUMERICSERV
163 If the
164 .Dv AI_NUMERICSERV
165 bit is set,
166 then a non-null
167 .Fa servname
168 string supplied shall be a numeric port string.
169 Otherwise, an
170 .Dv EAI_NONAME
171 error shall be returned.
172 This bit shall prevent any type of name resolution service
173 (for example, NIS+) from being invoked.
174 .It Dv AI_PASSIVE
175 If the
176 .Dv AI_PASSIVE
177 bit is set it indicates that the returned socket address structure
178 is intended for use in a call to
179 .Xr bind 2 .
180 In this case, if the
181 .Fa hostname
182 argument is the null pointer, then the IP address portion of the
183 socket address structure will be set to
184 .Dv INADDR_ANY
185 for an IPv4 address or
186 .Dv IN6ADDR_ANY_INIT
187 for an IPv6 address.
188 .Pp
189 If the
190 .Dv AI_PASSIVE
191 bit is not set, the returned socket address structure will be ready
192 for use in a call to
193 .Xr connect 2
194 for a connection-oriented protocol or
195 .Xr connect 2 ,
196 .Xr sendto 2 ,
197 or
198 .Xr sendmsg 2
199 if a connectionless protocol was chosen.
200 The
201 .Tn IP
202 address portion of the socket address structure will be set to the
203 loopback address if
204 .Fa hostname
205 is the null pointer and
206 .Dv AI_PASSIVE
207 is not set.
208 .El
209 .El
210 .Pp
211 All other elements of the
212 .Li addrinfo
213 structure passed via
214 .Fa hints
215 must be zero or the null pointer.
216 .Pp
217 If
218 .Fa hints
219 is the null pointer,
220 .Fn getaddrinfo
221 behaves as if the caller provided a
222 .Li struct addrinfo
223 with
224 .Fa ai_family
225 set to
226 .Dv PF_UNSPEC
227 and all other elements set to zero or
228 .Dv NULL .
229 .Pp
230 After a successful call to
231 .Fn getaddrinfo ,
232 .Fa *res
233 is a pointer to a linked list of one or more
234 .Li addrinfo
235 structures.
236 The list can be traversed by following the
237 .Fa ai_next
238 pointer in each
239 .Li addrinfo
240 structure until a null pointer is encountered.
241 The three members
242 .Fa ai_family ,
243 .Fa ai_socktype ,
244 and
245 .Fa ai_protocol
246 in each returned
247 .Li addrinfo
248 structure are suitable for a call to
249 .Xr socket 2 .
250 For each
251 .Li addrinfo
252 structure in the list, the
253 .Fa ai_addr
254 member points to a filled-in socket address structure of length
255 .Fa ai_addrlen .
256 .Pp
257 This implementation of
258 .Fn getaddrinfo
259 allows numeric IPv6 address notation with scope identifier,
260 as documented in chapter 11 of draft-ietf-ipv6-scoping-arch-02.txt.
261 By appending the percent character and scope identifier to addresses,
262 one can fill the
263 .Li sin6_scope_id
264 field for addresses.
265 This would make management of scoped addresses easier
266 and allows cut-and-paste input of scoped addresses.
267 .Pp
268 At this moment the code supports only link-local addresses with the format.
269 The scope identifier is hardcoded to the name of the hardware interface
270 associated
271 with the link
272 .Po
273 such as
274 .Li ne0
275 .Pc .
276 An example is
277 .Dq Li fe80::1%ne0 ,
278 which means
279 .Do
280 .Li fe80::1
281 on the link associated with the
282 .Li ne0
283 interface
284 .Dc .
285 .Pp
286 The current implementation assumes a one-to-one relationship between
287 the interface and link, which is not necessarily true from the specification.
288 .Pp
289 All of the information returned by
290 .Fn getaddrinfo
291 is dynamically allocated: the
292 .Li addrinfo
293 structures themselves as well as the socket address structures and
294 the canonical host name strings included in the
295 .Li addrinfo
296 structures.
297 .Pp
298 Memory allocated for the dynamically allocated structures created by
299 a successful call to
300 .Fn getaddrinfo
301 is released by the
302 .Fn freeaddrinfo
303 function.
304 The
305 .Fa ai
306 pointer should be a
307 .Li addrinfo
308 structure created by a call to
309 .Fn getaddrinfo .
310 .Sh RETURN VALUES
311 .Fn getaddrinfo
312 returns zero on success or one of the error codes listed in
313 .Xr gai_strerror 3
314 if an error occurs.
315 .Sh EXAMPLES
316 The following code tries to connect to
317 .Dq Li www.kame.net
318 service
319 .Dq Li http
320 via a stream socket.
321 It loops through all the addresses available, regardless of address family.
322 If the destination resolves to an IPv4 address, it will use an
323 .Dv AF_INET
324 socket.
325 Similarly, if it resolves to IPv6, an
326 .Dv AF_INET6
327 socket is used.
328 Observe that there is no hardcoded reference to a particular address family.
329 The code works even if
330 .Fn getaddrinfo
331 returns addresses that are not IPv4/v6.
332 .Bd -literal -offset indent
333 struct addrinfo hints, *res, *res0;
334 int error;
335 int s;
336 const char *cause = NULL;
338 memset(&hints, 0, sizeof(hints));
339 hints.ai_family = PF_UNSPEC;
340 hints.ai_socktype = SOCK_STREAM;
341 error = getaddrinfo("www.kame.net", "http", &hints, &res0);
342 if (error) {
343 errx(1, "%s", gai_strerror(error));
344 /*NOTREACHED*/
345 }
346 s = -1;
347 for (res = res0; res; res = res->ai_next) {
348 s = socket(res->ai_family, res->ai_socktype,
349 res->ai_protocol);
350 if (s < 0) {
351 cause = "socket";
352 continue;
353 }
355 if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
356 cause = "connect";
357 close(s);
358 s = -1;
359 continue;
360 }
362 break; /* okay we got one */
363 }
364 if (s < 0) {
365 err(1, "%s", cause);
366 /*NOTREACHED*/
367 }
368 freeaddrinfo(res0);
369 .Ed
370 .Pp
371 The following example tries to open a wildcard listening socket onto service
372 .Dq Li http ,
373 for all the address families available.
374 .Bd -literal -offset indent
375 struct addrinfo hints, *res, *res0;
376 int error;
377 int s[MAXSOCK];
378 int nsock;
379 const char *cause = NULL;
381 memset(&hints, 0, sizeof(hints));
382 hints.ai_family = PF_UNSPEC;
383 hints.ai_socktype = SOCK_STREAM;
384 hints.ai_flags = AI_PASSIVE;
385 error = getaddrinfo(NULL, "http", &hints, &res0);
386 if (error) {
387 errx(1, "%s", gai_strerror(error));
388 /*NOTREACHED*/
389 }
390 nsock = 0;
391 for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
392 s[nsock] = socket(res->ai_family, res->ai_socktype,
393 res->ai_protocol);
394 if (s[nsock] < 0) {
395 cause = "socket";
396 continue;
397 }
399 if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
400 cause = "bind";
401 close(s[nsock]);
402 continue;
403 }
404 (void) listen(s[nsock], 5);
406 nsock++;
407 }
408 if (nsock == 0) {
409 err(1, "%s", cause);
410 /*NOTREACHED*/
411 }
412 freeaddrinfo(res0);
413 .Ed
414 .Sh SEE ALSO
415 .Xr bind 2 ,
416 .Xr connect 2 ,
417 .Xr send 2 ,
418 .Xr socket 2 ,
419 .Xr gai_strerror 3 ,
420 .Xr gethostbyname 3 ,
421 .Xr getnameinfo 3 ,
422 .Xr getservbyname 3 ,
423 .Xr resolver 3 ,
424 .Xr hosts 5 ,
425 .Xr resolv.conf 5 ,
426 .Xr services 5 ,
427 .Xr hostname 7 ,
428 .Xr named 8
429 .Rs
430 .%A R. Gilligan
431 .%A S. Thomson
432 .%A J. Bound
433 .%A J. McCann
434 .%A W. Stevens
435 .%T Basic Socket Interface Extensions for IPv6
436 .%R RFC 3493
437 .%D February 2003
438 .Re
439 .Rs
440 .%A S. Deering
441 .%A B. Haberman
442 .%A T. Jinmei
443 .%A E. Nordmark
444 .%A B. Zill
445 .%T "IPv6 Scoped Address Architecture"
446 .%R internet draft
447 .%N draft-ietf-ipv6-scoping-arch-02.txt
448 .%O work in progress material
449 .Re
450 .Rs
451 .%A Craig Metz
452 .%T Protocol Independence Using the Sockets API
453 .%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
454 .%D June 2000
455 .Re
456 .Sh STANDARDS
457 The
458 .Fn getaddrinfo
459 function is defined by the
460 .St -p1003.1-2004
461 specification and documented in
462 .Dv "RFC 3493" ,
463 .Dq Basic Socket Interface Extensions for IPv6 .