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

NAME
     ggeettaaddddrriinnffoo, ffrreeeeaaddddrriinnffoo - socket address structure to host and service
     name

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

     void
     ffrreeeeaaddddrriinnffoo(struct addrinfo *ai);

DESCRIPTION
     The ggeettaaddddrriinnffoo() 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
     :

     struct addrinfo {
             int aiflags;           /* input flags */
             int aifamily;          /* protocol family for socket */
             int aisocktype;        /* socket type */
             int aiprotocol;        /* protocol for socket */
             socklent aiaddrlen;   /* length of socket-address */
             struct sockaddr *aiaddr; /* socket-address for socket */
             char *aicanonname;     /* canonical name for service location */
             struct addrinfo *ainext; /* 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:

     aifamily      The protocol family that should be used.  When aifamily
                    is set to PFUNSPEC, it means the caller will accept any
                    protocol family supported by the operating system.

     aisocktype    Denotes the type of socket that is wanted: SOCKSTREAM,
                    SOCKDGRAM, or SOCKRAW.  When aisocktype is zero the
                    caller will accept any socket type.

     aiprotocol    Indicates which transport protocol is desired, IPPROTOUDP
                    or IPPROTOTCP.  If aiprotocol is zero the caller will
                    accept any protocol.

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

                    AICANONNAME    If the AICANONNAME bit is set, a success-
                                    ful call to ggeettaaddddrriinnffoo() will return a
                                    NUL-terminated string containing the
                                    canonical name of the specified hostname
                                    in the aicanonname element of the first
                                    addrinfo structure returned.

                    AINUMERICHOST  If the AINUMERICHOST 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.

                    AIPASSIVE      If the AIPASSIVE 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 INADDRANY for an IPv4 address
                                    or IN6ADDRANYINIT for an IPv6 address.

                                    If the AIPASSIVE 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 AIPASSIVE 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, ggeettaaddddrriinnffoo() behaves as if the caller pro-
     vided a struct addrinfo with aifamily set to PFUNSPEC and all other
     elements set to zero or NULL.

     After a successful call to ggeettaaddddrriinnffoo(), *res is a pointer to a linked
     list of one or more addrinfo structures.  The list can be traversed by
     following the ainext pointer in each addrinfo structure until a null
     pointer is encountered.  The three members aifamily, aisocktype, and
     aiprotocol in each returned addrinfo structure are suitable for a call
     to socket(2).  For each addrinfo structure in the list, the aiaddr mem-
     ber points to a filled-in socket address structure of length aiaddrlen.

     This implementation of ggeettaaddddrriinnffoo() 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 sin6scopeid 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
     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 ggeettaaddddrriinnffoo() 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 ggeettaaddddrriinnffoo() is released by the ffrreeeeaaddddrriinnffoo() func-
     tion.  The ai pointer should be a addrinfo structure created by a call to
     ggeettaaddddrriinnffoo().

RETURN VALUES
     ggeettaaddddrriinnffoo() returns zero on success or one of the error codes listed in
     gaistrerror(3) if an error occurs.

EEXXAAMMPPLLEESS
     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 AFINET socket.  Similarly, if it resolves to
     IPv6, an AFINET6 socket is used.  Observe that there is no hardcoded
     reference to a particular address family.  The code works even if
     ggeettaaddddrriinnffoo() 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.aifamily = PFUNSPEC;
           hints.aisocktype = SOCKSTREAM;
           error = getaddrinfo("www.kame.net", "http", &hints, &res0);
           if (error) {
                   errx(1, "%s", gaistrerror(error));
                   /*NOTREACHED*/
           }
           s = -1;
           for (res = res0; res; res = res->ainext) {
                   s = socket(res->aifamily, res->aisocktype,
                       res->aiprotocol);
                   if (s < 0) {
                           cause = "socket";
                           continue;
                   }

                   if (connect(s, res->aiaddr, res->aiaddrlen) < 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 ser-
     vice ``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.aifamily = PFUNSPEC;
           hints.aisocktype = SOCKSTREAM;
           hints.aiflags = AIPASSIVE;
           error = getaddrinfo(NULL, "http", &hints, &res0);
           if (error) {
                   errx(1, "%s", gaistrerror(error));
                   /*NOTREACHED*/
           }
           nsock = 0;
           for (res = res0; res && nsock < MAXSOCK; res = res->ainext) {
                   s[nsock] = socket(res->aifamily, res->aisocktype,
                       res->aiprotocol);
                   if (s[nsock] < 0) {
                           cause = "socket";
                           continue;
                   }

                   if (bind(s[nsock], res->aiaddr, res->aiaddrlen) < 0) {
                           cause = "bind";
                           close(s[nsock]);
                           continue;
                   }
                   (void) listen(s[nsock], 5);

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

SEE ALSO
     bind(2), connect(2), send(2), socket(2), gaistrerror(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 material.

     Craig Metz, "Protocol Independence Using the Sockets API", Proceedings of
     the freenix track: 2000 USENIX annual technical conference, June 2000.

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

BUGS
     The implementation of ggeettaaddddrriinnffoo() is not thread-safe.

BSD                            December 20, 2004                           BSD