GETADDRINFO(3)            OpenBSD Programmer's Manual           GETADDRINFO(3)

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



SYNOPSIS
     #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 gethostby-
     name(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 spec-
     ified.  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 ar-
     gument 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 pro-
     cess each addrinfo structure in this list by following the ai_next point-
     er, 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 ad-
     dress 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 struc-
     ture, 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 ad-
     dress 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 struc-
     ture, 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 pre-
     vents any type of name resolution service (e.g., the DNS) from being
     called.

     All of the information returned by getaddrinfo() is dynamically allocat-
     ed: 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.

FILES
     /etc/hosts
     /etc/host.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_ADDRFAMILY  Address family for nodename not supported.
     EAI_AGAIN       Temporary failure in name resolution.
     EAI_BADFLAGS    Invalid value for ai_flags.
     EAI_FAIL        Non-recoverable failure in name resolution.
     EAI_FAMILY      ai_family not supported.
     EAI_MEMORY      Memory allocation failure.


     EAI_NODATA      No address associated with nodename.
     EAI_NONAME      nodename nor servname provided, or not known.
     EAI_SERVICE     servname not supported for ai_socktype.
     EAI_SOCKTYPE    ai_socktype not supported.
     EAI_SYSTEM      System error returned in errno.

     If called with proper 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
     getnameinfo(3),  gethostbyname(3),  getservbyname(3),  hosts(5),
     services(5),  hostname(7),  named(8)

     R. Gilligan, S.  Thomson, J. Bound, and W. Stevens, ``Basic Socket Inter-
     face Extensions for IPv6,'' RFC2553, March 1999.

STANDARDS
     The getaddrinfo() function is defined IEEE POSIX 1003.1g draft specifica-
     tion, and documented in ``Basic Socket Interface Extensions for IPv6''
     (RFC2533).

BUGS
     The text was shamelessly copied from RFC2553.

OpenBSD 2.6                      May 25, 1995                                3