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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27 .Nd socket address structure to host and service name
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; /* address 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 address family that should be used.
102 it means the caller will accept any address 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.
281 structure contains three members that are suitable for a call to
289 structure in the list, the
291 member points to a filled-in socket address structure of length
294 This implementation of
296 allows numeric IPv6 address notation with scope identifier,
297 as documented in chapter 11 of RFC 4007.
298 By appending the percent character and scope identifier to addresses,
302 This would make management of scoped addresses easier
303 and allows cut-and-paste input of scoped addresses.
305 At this moment the code supports only link-local addresses with the format.
306 The scope identifier is hardcoded to the name of the hardware interface
318 on the link associated with the
323 The current implementation assumes a one-to-one relationship between
324 the interface and link, which is not necessarily true from the specification.
326 All of the information returned by
328 is dynamically allocated: the
330 structures themselves as well as the socket address structures and
331 the canonical host name strings included in the
335 Memory allocated for the dynamically allocated structures created by
345 structure created by a call to
349 returns zero on success or one of the error codes listed in
353 The following code tries to connect to
358 It loops through all the addresses available, regardless of address family.
359 If the destination resolves to an IPv4 address, it will use an
362 Similarly, if it resolves to IPv6, an
365 Observe that there is no hardcoded reference to a particular address family.
366 The code works even if
368 returns addresses that are not IPv4/v6.
369 .Bd -literal -offset indent
370 struct addrinfo hints, *res, *res0;
373 const char *cause = NULL;
375 memset(&hints, 0, sizeof(hints));
376 hints.ai_family = AF_UNSPEC;
377 hints.ai_socktype = SOCK_STREAM;
378 error = getaddrinfo("www.kame.net", "http", &hints, &res0);
380 errx(1, "%s", gai_strerror(error));
384 for (res = res0; res; res = res->ai_next) {
385 s = socket(res->ai_family, res->ai_socktype,
392 if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
399 break; /* okay we got one */
408 The following example tries to open a wildcard listening socket onto service
410 for all the address families available.
411 .Bd -literal -offset indent
412 struct addrinfo hints, *res, *res0;
416 const char *cause = NULL;
418 memset(&hints, 0, sizeof(hints));
419 hints.ai_family = AF_UNSPEC;
420 hints.ai_socktype = SOCK_STREAM;
421 hints.ai_flags = AI_PASSIVE;
422 error = getaddrinfo(NULL, "http", &hints, &res0);
424 errx(1, "%s", gai_strerror(error));
428 for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
429 s[nsock] = socket(res->ai_family, res->ai_socktype,
436 if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
441 (void) listen(s[nsock], 5);
457 .Xr gethostbyname 3 ,
459 .Xr getservbyname 3 ,
472 .%T Basic Socket Interface Extensions for IPv6
482 .%T "IPv6 Scoped Address Architecture"
488 .%T Protocol Independence Using the Sockets API
489 .%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
495 function is defined by the
497 specification and documented in
499 .Dq Basic Socket Interface Extensions for IPv6 .