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GETADDRINFO(3)	       FreeBSD Library Functions Manual		GETADDRINFO(3)

NAME
     getaddrinfo, freeaddrinfo -- host and service name	to socket address
     structure

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netdb.h>

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

     void
     freeaddrinfo(struct addrinfo *ai);

DESCRIPTION
     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	deci-
     mal 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	family that should be used.  When ai_family is
		    set	to AF_UNSPEC, it means the caller will accept any ad-
		    dress family supported by the operating system.

     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_ADDRCONFIG   If the AI_ADDRCONFIG bit is	set, IPv4 ad-
				    dresses will be returned only if an	IPv4
				    address is configured on an	interface, and
				    IPv6 addresses will	be returned only if an
				    IPv6 address is configured on an inter-
				    face.  Addresses on	a loopback interface
				    and	link-local IPv6	addresses are not con-
				    sidered valid as configured	addresses.
				    This bit is	only considered	when determin-
				    ing	whether	a DNS query should be per-
				    formed or not.

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

		    AI_FQDN	    If the AI_FQDN bit is set, a successful
				    call to getaddrinfo() will return a	NUL-
				    terminated string containing the fully
				    qualified domain name of the specified
				    host name in the ai_canonname element of
				    the	first addrinfo structure returned.

				    This is different from the AI_CANONNAME
				    bit	flag that returns the canonical	name
				    registered in DNS, which may be different
				    from the fully qualified domain name that
				    the	host name resolved to.	Only one of
				    the	AI_FQDN	and AI_CANONNAME bits can be
				    set.

		    AI_NUMERICHOST  If the AI_NUMERICHOST bit is set, it indi-
				    cates 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 indi-
				    cates that servname	should be treated as a
				    numeric port string	and no service name
				    resolution should be attempted.

		    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 por-
				    tion 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 re-
				    turned 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 ad-
				    dress 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 pointer.

     If	hints is the null pointer, getaddrinfo() behaves as if the caller pro-
     vided a struct addrinfo with ai_family set	to AF_UNSPEC, ai_flags set to
     AI_ADDRCONFIG, 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 mem-
     ber points	to a filled-in socket address structure	of length ai_addrlen.

     This implementation of getaddrinfo() allows numeric IPv6 address notation
     with scope	identifier, as documented in RFC 4007.	By appending the per-
     cent 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 for-
     mat.  The scope identifier	is hardcoded to	the name of the	hardware in-
     terface 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 allo-
     cated: 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()	func-
     tion.  The	ai pointer should be an	addrinfo structure created by a	call
     to	getaddrinfo().

RETURN VALUES
     getaddrinfo() returns zero	on success or one of the error codes listed in
     gai_strerror(3) if	an error occurs.  If an	error occurs, no memory	is al-
     located by	getaddrinfo(), therefore it is not necessary to	release	the
     addrinfo structure(s).

EXAMPLES
     The following code	tries to connect to "www.kame.net" service "www" 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()	re-
     turns addresses that are not IPv4/v6.

	   struct addrinfo hints, *res,	*res0;
	   int error;
	   int save_errno;
	   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", "www", &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,
		       res->ai_protocol);
		   if (s == -1)	{
			   cause = "socket";
			   continue;
		   }

		   if (connect(s, res->ai_addr,	res->ai_addrlen) == -1)	{
			   cause = "connect";
			   save_errno =	errno;
			   close(s);
			   errno = save_errno;
			   s = -1;
			   continue;
		   }

		   break;  /* okay we got one */
	   }
	   if (s == -1)
		   err(1, "%s",	cause);
	   freeaddrinfo(res0);

     The following example tries to open a wildcard listening socket onto ser-
     vice "www", for all the address families available.

	   struct addrinfo hints, *res,	*res0;
	   int error;
	   int save_errno;
	   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, "www", &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,
		       res->ai_protocol);
		   if (s[nsock]	== -1) {
			   cause = "socket";
			   continue;
		   }

		   if (bind(s[nsock], res->ai_addr, res->ai_addrlen) ==	-1) {
			   cause = "bind";
			   save_errno =	errno;
			   close(s[nsock]);
			   errno = save_errno;
			   continue;
		   }
		   (void) listen(s[nsock], 5);

		   nsock++;
	   }
	   if (nsock ==	0)
		   err(1, "%s",	cause);
	   freeaddrinfo(res0);

SEE ALSO
     bind(2), connect(2), send(2), socket(2), gai_strerror(3),
     gethostbyname(3), getnameinfo(3), getservbyname(3), res_init(3),
     hosts(5), resolv.conf(5), services(5), hostname(7)

     Craig Metz, "Protocol Independence	Using the Sockets API",	Proceedings of
     the Freenix Track:	2000 USENIX Annual Technical Conference, June 2000.

STANDARDS
     The getaddrinfo() function	is defined by the IEEE Std 1003.1g-2000
     ("POSIX.1") draft specification and documented in RFC 3493.

     The AI_FQDN flag bit first	appeared in Windows 7.

     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, RFC 4007, March 2005.

FreeBSD	13.0			August 30, 2019			  FreeBSD 13.0

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | SEE ALSO | STANDARDS

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