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NetBSD 6.1.5 - man page for getaddrinfo (netbsd section 3)

GETADDRINFO(3)			   BSD Library Functions Manual 		   GETADDRINFO(3)

     getaddrinfo, freeaddrinfo, allocaddrinfo -- host and service name to socket address struc-

     #include <netdb.h>

     getaddrinfo(const char * restrict hostname, const char * restrict servname,
	 const struct addrinfo * restrict hints, struct addrinfo ** restrict res);

     freeaddrinfo(struct addrinfo *ai);

     struct addrinfo *
     allocaddrinfo(socklen_t len);

     The getaddrinfo() function is used to get a list of IP addresses and port numbers for host
     hostname and service servname.  It is a replacement for and provides more flexibility than
     the gethostbyname(3) and getservbyname(3) functions.

     The hostname and servname arguments are either pointers to NUL-terminated strings or the
     null pointer.  An acceptable value for hostname is either a valid host name or a numeric
     host address string consisting of a dotted decimal IPv4 address or an IPv6 address.  The
     servname is either a decimal port number or a service name listed in services(5).	At least
     one of hostname and servname must be non-null.

     hints is an optional pointer to a struct addrinfo, as defined by <netdb.h>:

     struct addrinfo {
	     int ai_flags;	     /* input flags */
	     int ai_family;	     /* address family for socket */
	     int ai_socktype;	     /* socket type */
	     int ai_protocol;	     /* protocol for socket */
	     socklen_t ai_addrlen;   /* length of socket-address */
	     struct sockaddr *ai_addr; /* socket-address for socket */
	     char *ai_canonname;     /* canonical name for service location */
	     struct addrinfo *ai_next; /* pointer to next in list */

     This structure can be used to provide hints concerning the type of socket that the caller
     supports or wishes to use.  The caller can supply the following structure elements in hints:

     ai_family	    The address (and protocol) family that should be used.  When ai_family is set
		    to AF_UNSPEC, it means the caller will accept any address family supported by
		    the operating system.  Note that while address families (AF_*) and protocol
		    families (PF_*) are theoretically distinct, in practice the distinction has
		    been lost.	RFC 3493 defines getaddrinfo() in terms of the address family
		    constants AF_* even though ai_family is to be passed as a protocol family to

     ai_socktype    Denotes the type of socket that is wanted: SOCK_STREAM, SOCK_DGRAM, or
		    SOCK_RAW.  When ai_socktype is zero the caller will accept any socket type.

     ai_protocol    Indicates which transport protocol is desired, IPPROTO_UDP or IPPROTO_TCP.
		    If ai_protocol is zero the caller will accept any protocol.

     ai_flags	    ai_flags is formed by OR'ing the following values:

		    AI_CANONNAME    If the AI_CANONNAME bit is set, a successful call to
				    getaddrinfo() will return a NUL-terminated string containing
				    the canonical name of the specified hostname in the
				    ai_canonname element of the first addrinfo structure

		    AI_NUMERICHOST  If the AI_NUMERICHOST bit is set, it indicates that hostname
				    should be treated as a numeric string defining an IPv4 or
				    IPv6 address and no name resolution should be attempted.

		    AI_NUMERICSERV  If the AI_NUMERICSERV bit is set, it indicates that the
				    servname string contains a numeric port number.  This is used
				    to prevent service name resolution.

		    AI_PASSIVE	    If the AI_PASSIVE bit is set it indicates that the returned
				    socket address structure is intended for use in a call to
				    bind(2).  In this case, if the hostname argument is the null
				    pointer, then the IP address portion of the socket address
				    structure will be set to INADDR_ANY for an IPv4 address or
				    IN6ADDR_ANY_INIT for an IPv6 address.

				    If the AI_PASSIVE bit is not set, the returned socket address
				    structure will be ready for use in a call to connect(2) for a
				    connection-oriented protocol or connect(2), sendto(2), or
				    sendmsg(2) if a connectionless protocol was chosen.  The IP
				    address portion of the socket address structure will be set
				    to the loopback address if hostname is the null pointer and
				    AI_PASSIVE is not set.

     All other elements of the addrinfo structure passed via hints must be zero or the null

     If hints is the null pointer, getaddrinfo() behaves as if the caller provided a struct
     addrinfo with ai_family set to AF_UNSPEC and all other elements set to zero or NULL.

     After a successful call to getaddrinfo(), *res is a pointer to a linked list of one or more
     addrinfo structures.  The list can be traversed by following the ai_next pointer in each
     addrinfo structure until a null pointer is encountered.  The three members ai_family,
     ai_socktype, and ai_protocol in each returned addrinfo structure are suitable for a call to
     socket(2).  For each addrinfo structure in the list, the ai_addr member points to a filled-
     in socket address structure of length ai_addrlen.

     This implementation of getaddrinfo() allows numeric IPv6 address notation with scope identi-
     fier, as documented in chapter 11 of draft-ietf-ipv6-scoping-arch-02.txt.	By appending the
     percent character and scope identifier to addresses, one can fill the sin6_scope_id field
     for addresses.  This would make management of scoped addresses easier and allows cut-and-
     paste input of scoped addresses.

     At this moment the code supports only link-local addresses with the format.  The scope iden-
     tifier is hardcoded to the name of the hardware interface associated with the link (such as
     ne0).  An example is ``fe80::1%ne0'', which means ``fe80::1 on the link associated with the
     ne0 interface''.

     The current implementation assumes a one-to-one relationship between the interface and link,
     which is not necessarily true from the specification.

     All of the information returned by getaddrinfo() is dynamically allocated: the addrinfo
     structures themselves as well as the socket address structures and the canonical host name
     strings included in the addrinfo structures.

     Memory allocated for the dynamically allocated structures created by a successful call to
     getaddrinfo() is released by the freeaddrinfo() function.	The ai pointer should be an
     addrinfo structure created by a call to getaddrinfo() or allocaddrinfo().	The
     allocaddrinfo() function is intended primarily for authors of nsdispatch(3) plugins imple-
     menting getaddrinfo() backends.  allocaddrinfo() allocates a struct addrinfo in a way that
     is compatible with being returned from getaddrinfo() and being ultimately freed by
     freeaddrinfo().  The returned structure is zeroed, except for the ai_addr field, which will
     point to len bytes of memory for storage of a socket address.  It is safe to allocate memory
     separately for ai_canonname with malloc(3), or in any other way that is compatible with
     deallocation by free(3).

     getaddrinfo() returns zero on success or one of the error codes listed in gai_strerror(3) if
     an error occurs.

     The following code tries to connect to ``www.kame.net'' service ``http'' via a stream
     socket.  It loops through all the addresses available, regardless of address family.  If the
     destination resolves to an IPv4 address, it will use an AF_INET socket.  Similarly, if it
     resolves to IPv6, an AF_INET6 socket is used.  Observe that there is no hardcoded reference
     to a particular address family.  The code works even if getaddrinfo() returns addresses that
     are not IPv4/v6.

	   struct addrinfo hints, *res, *res0;
	   int error;
	   int s;
	   const char *cause = NULL;

	   memset(&hints, 0, sizeof(hints));
	   hints.ai_family = AF_UNSPEC;
	   hints.ai_socktype = SOCK_STREAM;
	   error = getaddrinfo("www.kame.net", "http", &hints, &res0);
	   if (error) {
		   errx(1, "%s", gai_strerror(error));
	   s = -1;
	   for (res = res0; res; res = res->ai_next) {
		   s = socket(res->ai_family, res->ai_socktype,
		   if (s < 0) {
			   cause = "socket";

		   if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
			   cause = "connect";
			   s = -1;

		   break;  /* okay we got one */
	   if (s < 0) {
		   err(1, "%s", cause);

     The following example tries to open a wildcard listening socket onto service ``http'', for
     all the address families available.

	   struct addrinfo hints, *res, *res0;
	   int error;
	   int s[MAXSOCK];
	   int nsock;
	   const char *cause = NULL;

	   memset(&hints, 0, sizeof(hints));
	   hints.ai_family = AF_UNSPEC;
	   hints.ai_socktype = SOCK_STREAM;
	   hints.ai_flags = AI_PASSIVE;
	   error = getaddrinfo(NULL, "http", &hints, &res0);
	   if (error) {
		   errx(1, "%s", gai_strerror(error));
	   nsock = 0;
	   for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
		   s[nsock] = socket(res->ai_family, res->ai_socktype,
		   if (s[nsock] < 0) {
			   cause = "socket";

		   if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
			   cause = "bind";
		   (void) listen(s[nsock], 5);

	   if (nsock == 0) {
		   err(1, "%s", cause);

     bind(2), connect(2), send(2), socket(2), gai_strerror(3), gethostbyname(3), getnameinfo(3),
     getservbyname(3), resolver(3), hosts(5), resolv.conf(5), services(5), hostname(7), named(8)

     R. Gilligan, S. Thomson, J. Bound, J. McCann, and W. Stevens, Basic Socket Interface
     Extensions for IPv6, RFC 3493, February 2003.

     S. Deering, B. Haberman, T. Jinmei, E. Nordmark, and B. Zill, IPv6 Scoped Address
     Architecture, internet draft, draft-ietf-ipv6-scoping-arch-02.txt, work in progress

     Craig Metz, "Protocol Independence Using the Sockets API", Proceedings of the FREENIX Track:
     2000 USENIX Annual Technical Conference, USENIX Association,
     http://www.usenix.org/events/usenix2000/freenix/metzprotocol/metzprotocol.pdf, 99-108, June
     18-23, 2000.

     The getaddrinfo() function is defined by the IEEE Std 1003.1g-2000 (``POSIX.1'') draft spec-
     ification and documented in RFC 3493, ``Basic Socket Interface Extensions for IPv6''.

BSD					  April 17, 2010				      BSD

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