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 $
4 .\" Copyright (C) 2004 Internet Systems Consortium, Inc. ("ISC")
5 .\" Copyright (C) 2000, 2001 Internet Software Consortium.
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27 .Nd socket address structure to host and service name
29 .Fd #include <sys/types.h>
30 .Fd #include <sys/socket.h>
31 .Fd #include <netdb.h>
34 .Fa "const char *hostname" "const char *servname"
35 .Fa "const struct addrinfo *hints" "struct addrinfo **res"
38 .Fn freeaddrinfo "struct addrinfo *ai"
42 function is used to get a list of
44 addresses and port numbers for host
48 It is a replacement for and provides more flexibility than the
58 arguments are either pointers to NUL-terminated strings or the null pointer.
59 An acceptable value for
61 is either a valid host name or a numeric host address string consisting
62 of a dotted decimal IPv4 address or an IPv6 address.
65 is either a decimal port number or a service name listed in
74 is an optional pointer to a
80 int ai_flags; /* input flags */
81 int ai_family; /* protocol family for socket */
82 int ai_socktype; /* socket type */
83 int ai_protocol; /* protocol for socket */
84 socklen_t ai_addrlen; /* length of socket-address */
85 struct sockaddr *ai_addr; /* socket-address for socket */
86 char *ai_canonname; /* canonical name for service location */
87 struct addrinfo *ai_next; /* pointer to next in list */
91 This structure can be used to provide hints concerning the type of socket
92 that the caller supports or wishes to use.
93 The caller can supply the following structure elements in
95 .Bl -tag -width "ai_socktypeXX"
97 The protocol family that should be used.
102 it means the caller will accept any protocol family supported by the
105 Denotes the type of socket that is wanted:
112 is zero the caller will accept any socket type.
114 Indicates which transport protocol is desired,
120 is zero the caller will accept any protocol.
126 parameter points shall be set to zero
127 or be the bitwise-inclusive OR of one or more of the values
136 .Bl -tag -width "AI_CANONNAMEXX"
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.
147 flag is used with the
151 shall return all matching IPv6 and IPv4 addresses.
153 For example, when using the DNS, queries are made for both AAAA records and A records, and
155 returns the combined results of both queries.
156 Any IPv4 addresses found are returned as IPv4-mapped IPv6 addresses.
166 bit is set, a successful call to
168 will return a NUL-terminated string containing the canonical name
169 of the specified hostname in the
174 .It Dv AI_NUMERICHOST
177 bit is set, it indicates that
179 should be treated as a numeric string defining an IPv4 or IPv6 address
180 and no name resolution should be attempted.
181 .It Dv AI_NUMERICSERV
187 string supplied shall be a numeric port string.
190 error shall be returned.
191 This bit shall prevent any type of name resolution service
192 (for example, NIS+) from being invoked.
196 bit is set it indicates that the returned socket address structure
197 is intended for use in a call to
201 argument is the null pointer, then the IP address portion of the
202 socket address structure will be set to
204 for an IPv4 address or
210 bit is not set, the returned socket address structure will be ready
213 for a connection-oriented protocol or
218 if a connectionless protocol was chosen.
221 address portion of the socket address structure will be set to the
224 is the null pointer and
230 flag is specified along with an ai_family of
234 shall return IPv4-mapped IPv6 addresses on finding no matching IPv6 addresses (
238 For example, when using the DNS, if no AAAA records are found then a query is made for A records and any found are returned as IPv4-mapped IPv6 addresses.
242 flag shall be ignored unless
249 All other elements of the
253 must be zero or the null pointer.
259 behaves as if the caller provided a
265 and all other elements set to zero or
268 After a successful call to
271 is a pointer to a linked list of one or more
274 The list can be traversed by following the
278 structure until a null pointer is encountered.
286 structure are suitable for a call to
290 structure in the list, the
292 member points to a filled-in socket address structure of length
295 This implementation of
297 allows numeric IPv6 address notation with scope identifier,
298 as documented in chapter 11 of RFC 4007.
299 By appending the percent character and scope identifier to addresses,
303 This would make management of scoped addresses easier
304 and allows cut-and-paste input of scoped addresses.
306 At this moment the code supports only link-local addresses with the format.
307 The scope identifier is hardcoded to the name of the hardware interface
319 on the link associated with the
324 The current implementation assumes a one-to-one relationship between
325 the interface and link, which is not necessarily true from the specification.
327 All of the information returned by
329 is dynamically allocated: the
331 structures themselves as well as the socket address structures and
332 the canonical host name strings included in the
336 Memory allocated for the dynamically allocated structures created by
346 structure created by a call to
350 returns zero on success or one of the error codes listed in
354 The following code tries to connect to
359 It loops through all the addresses available, regardless of address family.
360 If the destination resolves to an IPv4 address, it will use an
363 Similarly, if it resolves to IPv6, an
366 Observe that there is no hardcoded reference to a particular address family.
367 The code works even if
369 returns addresses that are not IPv4/v6.
370 .Bd -literal -offset indent
371 struct addrinfo hints, *res, *res0;
374 const char *cause = NULL;
376 memset(&hints, 0, sizeof(hints));
377 hints.ai_family = PF_UNSPEC;
378 hints.ai_socktype = SOCK_STREAM;
379 error = getaddrinfo("www.kame.net", "http", &hints, &res0);
381 errx(1, "%s", gai_strerror(error));
385 for (res = res0; res; res = res->ai_next) {
386 s = socket(res->ai_family, res->ai_socktype,
393 if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
400 break; /* okay we got one */
409 The following example tries to open a wildcard listening socket onto service
411 for all the address families available.
412 .Bd -literal -offset indent
413 struct addrinfo hints, *res, *res0;
417 const char *cause = NULL;
419 memset(&hints, 0, sizeof(hints));
420 hints.ai_family = PF_UNSPEC;
421 hints.ai_socktype = SOCK_STREAM;
422 hints.ai_flags = AI_PASSIVE;
423 error = getaddrinfo(NULL, "http", &hints, &res0);
425 errx(1, "%s", gai_strerror(error));
429 for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
430 s[nsock] = socket(res->ai_family, res->ai_socktype,
437 if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
442 (void) listen(s[nsock], 5);
458 .Xr gethostbyname 3 ,
460 .Xr getservbyname 3 ,
473 .%T Basic Socket Interface Extensions for IPv6
483 .%T "IPv6 Scoped Address Architecture"
489 .%T Protocol Independence Using the Sockets API
490 .%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
496 function is defined by the
498 specification and documented in
500 .Dq Basic Socket Interface Extensions for IPv6 .