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

NAME
     getaddrinfo, freeaddrinfo, gai_strerror - nodename-to-address translation
     in protocol-independent manner

LIBRARY
     Standard C Library (libc, -lc)

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

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

     void
     freeaddrinfo(struct addrinfo *ai);

     char *
     gai_strerror(int ecode);

DESCRIPTION
     The getaddrinfo() function is defined for protocol-independent nodename-
     to-address translation.  It performs the functionality of
     gethostbyname(3) and getservbyname(3), but in a more sophisticated
     manner.

     The addrinfo structure is defined as a result of including the <netdb.h>
     header:

     struct addrinfo {
          int     ai_flags;     /* AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST */
          int     ai_family;    /* PF_xxx */
          int     ai_socktype;  /* SOCK_xxx */
          int     ai_protocol;  /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
          size_t  ai_addrlen;   /* length of ai_addr */
          char   *ai_canonname; /* canonical name for nodename */
          struct sockaddr  *ai_addr; /* binary address */
          struct addrinfo  *ai_next; /* next structure in linked list */
     };

     The nodename and servname arguments are pointers to null-terminated
     strings or NULL.  One or both of these two arguments must be a non-NULL
     pointer.  In the normal client scenario, both the nodename and servname
     are specified.  In the normal server scenario, only the servname is
     specified.  A non-NULL nodename string can be either a node name or a
     numeric host address string (i.e., a dotted-decimal IPv4 address or an
     IPv6 hex address).  A non-NULL servname string can be either a service
     name or a decimal port number.

     The caller can optionally pass an addrinfo structure, pointed to by the
     third argument, to provide hints concerning the type of socket that the
     caller supports.  In this hints structure all members other than
     ai_flags, ai_family, ai_socktype, and ai_protocol must be zero or a NULL
     pointer.  A value of PF_UNSPEC for ai_family means the caller will accept
     any protocol family.  A value of 0 for ai_socktype means the caller will
     accept any socket type.  A value of 0 for ai_protocol means the caller
     will accept any protocol.  For example, if the caller handles only TCP
     and not UDP, then the ai_socktype member of the hints structure should be
     set to SOCK_STREAM when getaddrinfo() is called.  If the caller handles
     only IPv4 and not IPv6, then the ai_family member of the hints structure
     should be set to PF_INET when getaddrinfo() is called.  If the third
     argument to getaddrinfo() is a NULL pointer, this is the same as if the
     caller had filled in an addrinfo structure initialized to zero with
     ai_family set to PF_UNSPEC.

     Upon successful return a pointer to a linked list of one or more addrinfo
     structures is returned through the final argument.  The caller can
     process each addrinfo structure in this list by following the ai_next
     pointer, until a NULL pointer is encountered.  In each returned addrinfo
     structure the three members ai_family, ai_socktype, and ai_protocol are
     the corresponding arguments for a call to the socket() function.  In each
     addrinfo structure the ai_addr member points to a filled-in socket
     address structure whose length is specified by the ai_addrlen member.

     If the AI_PASSIVE bit is set in the ai_flags member of the hints
     structure, then the caller plans to use the returned socket address
     structure in a call to bind().  In this case, if the nodename argument is
     a 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 in the ai_flags member of the hints
     structure, then the returned socket address structure will be ready for a
     call to connect() (for a connection-oriented protocol) or either
     connect(), sendto(), or sendmsg() (for a connectionless protocol).  In
     this case, if the nodename argument is a NULL pointer, then the IP
     address portion of the socket address structure will be set to the
     loopback address.

     If the AI_CANONNAME bit is set in the ai_flags member of the hints
     structure, then upon successful return the ai_canonname member of the
     first addrinfo structure in the linked list will point to a null-
     terminated string containing the canonical name of the specified
     nodename.

     If the AI_NUMERICHOST bit is set in the ai_flags member of the hints
     structure, then a non-NULL nodename string must be a numeric host address
     string.  Otherwise an error of EAI_NONAME is returned.  This flag
     prevents any type of name resolution service (e.g., the DNS) from being
     called.

     The arguments to getaddrinfo() must be sufficiently consistent and
     unambiguous.  Here are some problem cases you may encounter:

     +o   The getaddrinfo() function will fail if the members in the hints
         structure are not consistent.  For example, for internet address
         families, getaddrinfo() will fail if you specify SOCK_STREAM to
         ai_socktype while you specify IPPROTO_UDP to ai_protocol.

     +o   If you specify a servname which is defined only for certain
         ai_socktype, getaddrinfo() will fail because the arguments are not
         consistent.  For example, getaddrinfo() will return an error if you
         ask for ``tftp'' service on SOCK_STREAM.

     +o   For internet address families, if you specify servname while you set
         ai_socktype to SOCK_RAW, getaddrinfo() will fail, because service
         names are not defined for the internet SOCK_RAW space.

     +o   If you specify numeric servname, while leaving ai_socktype and
         ai_protocol unspecified, getaddrinfo() will fail.  This is because
         the numeric servname does not identify any socket type, and
         getaddrinfo() is not allowed to glob the argument in such case.

     All of the information returned by getaddrinfo() is dynamically
     allocated: the addrinfo structures, the socket address structures, and
     canonical node name strings pointed to by the addrinfo structures.  To
     return this information to the system the function freeaddrinfo() is
     called.  The addrinfo structure pointed to by the ai argument is freed,
     along with any dynamic storage pointed to by the structure.  This
     operation is repeated until a NULL ai_next pointer is encountered.

     To aid applications in printing error messages based on the EAI_xxx codes
     returned by getaddrinfo(), gai_strerror() is defined.  The argument is
     one of the EAI_xxx values defined earlier and the return value points to
     a string describing the error.  If the argument is not one of the EAI_xxx
     values, the function still returns a pointer to a string whose contents
     indicate an unknown error.

EXTENSIONS
     This implementation supports numeric IPv6 address notation with the
     experimental scope identifier.  By appending a percent sign and scope
     identifier to the address, you can specify the value of the sin6_scope_id
     field of the socket address.  This makes management of scoped address
     easier, and allows cut-and-paste input of scoped addresses.

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

     This implementation is still very experimental and non-standard.  The
     current implementation assumes a one-to-one relationship between
     interfaces and links, which is not necessarily true according to the
     specification.

EXAMPLES
     The following code tries to connect to ``www.kame.net'' service ``http''.
     via stream socket.  It loops through all the addresses available,
     regardless of the 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 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 = PF_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;
           cause = "no addresses";
           errno = EADDRNOTAVAIL;
           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, 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 = PF_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;
                   }

                   if (listen(s[nsock], SOMAXCONN) < 0) {
                           cause = "listen";
                           close(s[nsock]);
                           continue;
                   }

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

FILES
     /etc/hosts
     /etc/nsswitch.conf
     /etc/resolv.conf

DIAGNOSTICS
     Error return status from getaddrinfo() is zero on success and non-zero on
     errors.  Non-zero error codes are defined in <netdb.h>, and as follows:

     EAI_AGAIN       Temporary failure in name resolution.
     EAI_BADFLAGS    Invalid value for ai_flags.
     EAI_FAIL        Non-recoverable failure in name resolution.
     EAI_FAMILY      The ai_family address family is not supported.
     EAI_MEMORY      Memory allocation failure.
     EAI_NONAME      Neither nodename nor servname provided, or not known.
     EAI_SERVICE     The servname service name is not supported for
                     ai_socktype.
     EAI_SOCKTYPE    The ai_socktype socket type is not supported.
     EAI_SYSTEM      System error returned in errno.
     EAI_BADHINTS    Invalid value for hints.
     EAI_PROTOCOL    Resolved protocol is unknown.
     EAI_MAX         Unknown error.

     If called with an appropriate argument, gai_strerror() returns a pointer
     to a string describing the given error code.  If the argument is not one
     of the EAI_xxx values, the function still returns a pointer to a string
     whose contents indicate an unknown error.

SEE ALSO
     gethostbyname(3), getnameinfo(3), getservbyname(3), hosts(5),
     resolv.conf(5), services(5), hostname(7), named(8)

     R. Gilligan, S. Thomson, J. Bound, and W. Stevens, Basic Socket Interface
     Extensions for IPv6, RFC2553, March 1999.

     Tatsuya Jinmei and Atsushi Onoe, An Extension of Format for IPv6 Scoped
     Addresses, internet draft, draft-ietf-ipngwg-scopedaddr-format-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.

HISTORY
     The implementation first appeared in WIDE Hydrangea IPv6 protocol stack
     kit.

STANDARDS
     The getaddrinfo() function is defined in IEEE Std 1003.1g-2000
     (``POSIX.1g''), and documented in ``Basic Socket Interface Extensions for
     IPv6'' (RFC2553).

BUGS
     Though the current implementation should be thread-safe, using
     getaddrinfo() in conjunction with gethostby*() breaks thread-safeness.

     The text was shamelessly copied from RFC2553.

FreeBSD 11.0-PRERELEASE          May 25, 1995          FreeBSD 11.0-PRERELEASE

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | EXTENSIONS | EXAMPLES | FILES | DIAGNOSTICS | SEE ALSO | HISTORY | STANDARDS | BUGS

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