lookup.subproj/getaddrinfo.3

   1 .\"     $NetBSD: getaddrinfo.3,v 1.39 2005/01/11 06:01:41 itojun Exp $
   2 .\"     $KAME: getaddrinfo.3,v 1.36 2005/01/05 03:23:05 itojun Exp $
   3 .\"     $OpenBSD: getaddrinfo.3,v 1.35 2004/12/21 03:40:31 jaredy Exp $
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   5 .\" Copyright (C) 2004  Internet Systems Consortium, Inc. ("ISC")
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  20 .Dd December 20, 2004
  21 .Dt GETADDRINFO 3
  22 .Os
  23 .Sh NAME
  24 .Nm getaddrinfo ,
  25 .Nm freeaddrinfo
  26 .Nd socket address structure to host and service name
  27 .Sh SYNOPSIS
  28 .Fd #include <sys/types.h>
  29 .Fd #include <sys/socket.h>
  30 .Fd #include <netdb.h>
  31 .Ft int
  32 .Fn getaddrinfo "const char *hostname" "const char *servname" \
  33     "const struct addrinfo *hints" "struct addrinfo **res"
  34 .Ft void
  35 .Fn freeaddrinfo "struct addrinfo *ai"
  36 .Sh DESCRIPTION
  37 The
  38 .Fn getaddrinfo
  39 function is used to get a list of
  40 .Tn IP
  41 addresses and port numbers for host
  42 .Fa hostname
  43 and service
  44 .Fa servname .
  45 It is a replacement for and provides more flexibility than the
  46 .Xr gethostbyname 3
  47 and
  48 .Xr getservbyname 3
  49 functions.
  50 .Pp
  51 The
  52 .Fa hostname
  53 and
  54 .Fa servname
  55 arguments are either pointers to NUL-terminated strings or the null pointer.
  56 An acceptable value for
  57 .Fa hostname
  58 is either a valid host name or a numeric host address string consisting
  59 of a dotted decimal IPv4 address or an IPv6 address.
  60 The
  61 .Fa servname
  62 is either a decimal port number or a service name listed in
  63 .Xr services 5 .
  64 At least one of
  65 .Fa hostname
  66 and
  67 .Fa servname
  68 must be non-null.
  69 .Pp
  70 .Fa hints
  71 is an optional pointer to a
  72 .Li struct addrinfo ,
  73 as defined by
  74 .Aq Pa netdb.h :
  75 .Bd -literal
  76 struct addrinfo {
  77         int ai_flags;           /* input flags */
  78         int ai_family;          /* protocol family for socket */
  79         int ai_socktype;        /* socket type */
  80         int ai_protocol;        /* protocol for socket */
  81         socklen_t ai_addrlen;   /* length of socket-address */
  82         struct sockaddr *ai_addr; /* socket-address for socket */
  83         char *ai_canonname;     /* canonical name for service location */
  84         struct addrinfo *ai_next; /* pointer to next in list */
  85 };
  86 .Ed
  87 .Pp
  88 This structure can be used to provide hints concerning the type of socket
  89 that the caller supports or wishes to use.
  90 The caller can supply the following structure elements in
  91 .Fa hints :
  92 .Bl -tag -width "ai_socktypeXX"
  93 .It Fa ai_family
  94 The protocol family that should be used.
  95 When
  96 .Fa ai_family
  97 is set to
  98 .Dv PF_UNSPEC ,
  99 it means the caller will accept any protocol family supported by the
 100 operating system.
 101 .It Fa ai_socktype
 102 Denotes the type of socket that is wanted:
 103 .Dv SOCK_STREAM ,
 104 .Dv SOCK_DGRAM ,
 105 or
 106 .Dv SOCK_RAW .
 107 When
 108 .Fa ai_socktype
 109 is zero the caller will accept any socket type.
 110 .It Fa ai_protocol
 111 Indicates which transport protocol is desired,
 112 .Dv IPPROTO_UDP
 113 or
 114 .Dv IPPROTO_TCP .
 115 If
 116 .Fa ai_protocol
 117 is zero the caller will accept any protocol.
 118 .It Fa ai_flags
 119 .Fa ai_flags
 120 is formed by
 121 .Tn OR Ns 'ing
 122 the following values:
 123 .Bl -tag -width "AI_CANONNAMEXX"
 124 .It Dv AI_CANONNAME
 125 If the
 126 .Dv AI_CANONNAME
 127 bit is set, a successful call to
 128 .Fn getaddrinfo
 129 will return a NUL-terminated string containing the canonical name
 130 of the specified hostname in the
 131 .Fa ai_canonname
 132 element of the first
 133 .Li addrinfo
 134 structure returned.
 135 .It Dv AI_NUMERICHOST
 136 If the
 137 .Dv AI_NUMERICHOST
 138 bit is set, it indicates that
 139 .Fa hostname
 140 should be treated as a numeric string defining an IPv4 or IPv6 address
 141 and no name resolution should be attempted.
 142 .It Dv AI_PASSIVE
 143 If the
 144 .Dv AI_PASSIVE
 145 bit is set it indicates that the returned socket address structure
 146 is intended for use in a call to
 147 .Xr bind 2 .
 148 In this case, if the
 149 .Fa hostname
 150 argument is the null pointer, then the IP address portion of the
 151 socket address structure will be set to
 152 .Dv INADDR_ANY
 153 for an IPv4 address or
 154 .Dv IN6ADDR_ANY_INIT
 155 for an IPv6 address.
 156 .Pp
 157 If the
 158 .Dv AI_PASSIVE
 159 bit is not set, the returned socket address structure will be ready
 160 for use in a call to
 161 .Xr connect 2
 162 for a connection-oriented protocol or
 163 .Xr connect 2 ,
 164 .Xr sendto 2 ,
 165 or
 166 .Xr sendmsg 2
 167 if a connectionless protocol was chosen.
 168 The
 169 .Tn IP
 170 address portion of the socket address structure will be set to the
 171 loopback address if
 172 .Fa hostname
 173 is the null pointer and
 174 .Dv AI_PASSIVE
 175 is not set.
 176 .El
 177 .El
 178 .Pp
 179 All other elements of the
 180 .Li addrinfo
 181 structure passed via
 182 .Fa hints
 183 must be zero or the null pointer.
 184 .Pp
 185 If
 186 .Fa hints
 187 is the null pointer,
 188 .Fn getaddrinfo
 189 behaves as if the caller provided a
 190 .Li struct addrinfo
 191 with
 192 .Fa ai_family
 193 set to
 194 .Dv PF_UNSPEC
 195 and all other elements set to zero or
 196 .Dv NULL .
 197 .Pp
 198 After a successful call to
 199 .Fn getaddrinfo ,
 200 .Fa *res
 201 is a pointer to a linked list of one or more
 202 .Li addrinfo
 203 structures.
 204 The list can be traversed by following the
 205 .Fa ai_next
 206 pointer in each
 207 .Li addrinfo
 208 structure until a null pointer is encountered.
 209 The three members
 210 .Fa ai_family,
 211 .Fa ai_socktype,
 212 and
 213 .Fa ai_protocol
 214 in each returned
 215 .Li addrinfo
 216 structure are suitable for a call to
 217 .Xr socket 2 .
 218 For each
 219 .Li addrinfo
 220 structure in the list, the
 221 .Fa ai_addr
 222 member points to a filled-in socket address structure of length
 223 .Fa ai_addrlen .
 224 .Pp
 225 This implementation of
 226 .Fn getaddrinfo
 227 allows numeric IPv6 address notation with scope identifier,
 228 as documented in chapter 11 of draft-ietf-ipv6-scoping-arch-02.txt.
 229 By appending the percent character and scope identifier to addresses,
 230 one can fill the
 231 .Li sin6_scope_id
 232 field for addresses.
 233 This would make management of scoped addresses easier
 234 and allows cut-and-paste input of scoped addresses.
 235 .Pp
 236 At this moment the code supports only link-local addresses with the format.
 237 The scope identifier is hardcoded to the name of the hardware interface
 238 associated
 239 with the link
 240 .Po
 241 such as
 242 .Li ne0
 243 .Pc .
 244 An example is
 245 .Dq Li fe80::1%ne0 ,
 246 which means
 247 .Do
 248 .Li fe80::1
 249 on the link associated with the
 250 .Li ne0
 251 interface
 252 .Dc .
 253 .Pp
 254 The current implementation assumes a one-to-one relationship between
 255 the interface and link, which is not necessarily true from the specification.
 256 .Pp
 257 All of the information returned by
 258 .Fn getaddrinfo
 259 is dynamically allocated: the
 260 .Li addrinfo
 261 structures themselves as well as the socket address structures and
 262 the canonical host name strings included in the
 263 .Li addrinfo
 264 structures.
 265 .Pp
 266 Memory allocated for the dynamically allocated structures created by
 267 a successful call to
 268 .Fn getaddrinfo
 269 is released by the
 270 .Fn freeaddrinfo
 271 function.
 272 The
 273 .Fa ai
 274 pointer should be a
 275 .Li addrinfo
 276 structure created by a call to
 277 .Fn getaddrinfo .
 278 .Sh RETURN VALUES
 279 .Fn getaddrinfo
 280 returns zero on success or one of the error codes listed in
 281 .Xr gai_strerror 3
 282 if an error occurs.
 283 .Sh EXAMPLES
 284 The following code tries to connect to
 285 .Dq Li www.kame.net
 286 service
 287 .Dq Li http
 288 via a stream socket.
 289 It loops through all the addresses available, regardless of address family.
 290 If the destination resolves to an IPv4 address, it will use an
 291 .Dv AF_INET
 292 socket.
 293 Similarly, if it resolves to IPv6, an
 294 .Dv AF_INET6
 295 socket is used.
 296 Observe that there is no hardcoded reference to a particular address family.
 297 The code works even if
 298 .Fn getaddrinfo
 299 returns addresses that are not IPv4/v6.
 300 .Bd -literal -offset indent
 301 struct addrinfo hints, *res, *res0;
 302 int error;
 303 int s;
 304 const char *cause = NULL;
 305
 306 memset(&hints, 0, sizeof(hints));
 307 hints.ai_family = PF_UNSPEC;
 308 hints.ai_socktype = SOCK_STREAM;
 309 error = getaddrinfo("www.kame.net", "http", &hints, &res0);
 310 if (error) {
 311         errx(1, "%s", gai_strerror(error));
 312         /*NOTREACHED*/
 313 }
 314 s = -1;
 315 for (res = res0; res; res = res->ai_next) {
 316         s = socket(res->ai_family, res->ai_socktype,
 317             res->ai_protocol);
 318         if (s < 0) {
 319                 cause = "socket";
 320                 continue;
 321         }
 322
 323         if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
 324                 cause = "connect";
 325                 close(s);
 326                 s = -1;
 327                 continue;
 328         }
 329
 330         break;  /* okay we got one */
 331 }
 332 if (s < 0) {
 333         err(1, "%s", cause);
 334         /*NOTREACHED*/
 335 }
 336 freeaddrinfo(res0);
 337 .Ed
 338 .Pp
 339 The following example tries to open a wildcard listening socket onto service
 340 .Dq Li http ,
 341 for all the address families available.
 342 .Bd -literal -offset indent
 343 struct addrinfo hints, *res, *res0;
 344 int error;
 345 int s[MAXSOCK];
 346 int nsock;
 347 const char *cause = NULL;
 348
 349 memset(&hints, 0, sizeof(hints));
 350 hints.ai_family = PF_UNSPEC;
 351 hints.ai_socktype = SOCK_STREAM;
 352 hints.ai_flags = AI_PASSIVE;
 353 error = getaddrinfo(NULL, "http", &hints, &res0);
 354 if (error) {
 355         errx(1, "%s", gai_strerror(error));
 356         /*NOTREACHED*/
 357 }
 358 nsock = 0;
 359 for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
 360         s[nsock] = socket(res->ai_family, res->ai_socktype,
 361             res->ai_protocol);
 362         if (s[nsock] < 0) {
 363                 cause = "socket";
 364                 continue;
 365         }
 366
 367         if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
 368                 cause = "bind";
 369                 close(s[nsock]);
 370                 continue;
 371         }
 372         (void) listen(s[nsock], 5);
 373
 374         nsock++;
 375 }
 376 if (nsock == 0) {
 377         err(1, "%s", cause);
 378         /*NOTREACHED*/
 379 }
 380 freeaddrinfo(res0);
 381 .Ed
 382 .Sh SEE ALSO
 383 .Xr bind 2 ,
 384 .Xr connect 2 ,
 385 .Xr send 2 ,
 386 .Xr socket 2 ,
 387 .Xr gai_strerror 3 ,
 388 .Xr gethostbyname 3 ,
 389 .Xr getnameinfo 3 ,
 390 .Xr getservbyname 3 ,
 391 .Xr resolver 3 ,
 392 .Xr hosts 5 ,
 393 .Xr resolv.conf 5 ,
 394 .Xr services 5 ,
 395 .Xr hostname 7 ,
 396 .Xr named 8
 397 .Rs
 398 .%A R. Gilligan
 399 .%A S. Thomson
 400 .%A J. Bound
 401 .%A J. McCann
 402 .%A W. Stevens
 403 .%T Basic Socket Interface Extensions for IPv6
 404 .%R RFC 3493
 405 .%D February 2003
 406 .Re
 407 .Rs
 408 .%A S. Deering
 409 .%A B. Haberman
 410 .%A T. Jinmei
 411 .%A E. Nordmark
 412 .%A B. Zill
 413 .%T "IPv6 Scoped Address Architecture"
 414 .%R internet draft
 415 .%N draft-ietf-ipv6-scoping-arch-02.txt
 416 .%O work in progress material
 417 .Re
 418 .Rs
 419 .%A Craig Metz
 420 .%T Protocol Independence Using the Sockets API
 421 .%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
 422 .%D June 2000
 423 .Re
 424 .Sh STANDARDS
 425 The
 426 .Fn getaddrinfo
 427 function is defined by the
 428 .St -p1003.1g-2000
 429 draft specification and documented in
 430 .Dv "RFC 3493" ,
 431 .Dq Basic Socket Interface Extensions for IPv6 .
 432 .Sh BUGS
 433 The implementation of
 434 .Fn getaddrinfo
 435 is not thread-safe.