| GETADDRINFO(3) | Library Functions Manual | GETADDRINFO(3) | 
getaddrinfo, freeaddrinfo,
  allocaddrinfo —
#include <netdb.h>
int
  
  getaddrinfo(const
    char * restrict hostname,
    const char * restrict
    servname, const struct
    addrinfo * restrict hints,
    struct addrinfo ** restrict
    res);
void
  
  freeaddrinfo(struct
    addrinfo *ai);
struct addrinfo *
  
  allocaddrinfo(socklen_t
    len);
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:
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
      socket(2).SOCK_STREAM, SOCK_DGRAM,
      or SOCK_RAW. When
      ai_socktype is zero the caller will accept any
      socket type.IPPROTO_UDP or
      IPPROTO_TCP. If ai_protocol
      is zero the caller will accept any protocol.AI_CANONNAMEAI_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 returned.AI_NUMERICHOSTAI_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_NUMERICSERVAI_NUMERICSERV bit is set, it indicates
          that the servname string contains a numeric port
          number. This is used to prevent service name resolution.AI_PASSIVEAI_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.
AI_SRVAll 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 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.
By default IPv6 address entries are ordered before IPv4 ones, but the order of the entries in the list can be controlled using ip6addrctl(8).
This implementation of getaddrinfo()
    allows numeric IPv6 address notation with scope identifier, 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 identifier 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 implementing 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.
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));
	/*NOTREACHED*/
}
s = -1;
for (res = res0; res; res = res->ai_next) {
	s = socket(res->ai_family, res->ai_socktype,
	    res->ai_protocol);
	if (s < 0) {
		cause = "socket";
		continue;
	}
	if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
		cause = "connect";
		close(s);
		s = -1;
		continue;
	}
	break;	/* okay we got one */
}
if (s < 0) {
	err(1, "%s", cause);
	/*NOTREACHED*/
}
freeaddrinfo(res0);
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));
	/*NOTREACHED*/
}
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] < 0) {
		cause = "socket";
		continue;
	}
	if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
		cause = "bind";
		close(s[nsock]);
		continue;
	}
	(void) listen(s[nsock], 5);
	nsock++;
}
if (nsock == 0) {
	err(1, "%s", cause);
	/*NOTREACHED*/
}
freeaddrinfo(res0);
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 material.
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.
getaddrinfo() function is defined by the
  IEEE Std 1003.1g-2000 (“POSIX.1g”) draft
  specification and documented in RFC 3493,
  “Basic Socket Interface Extensions for IPv6”.
| December 13, 2015 | NetBSD 9.3 |