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

NAME
     getnameinfo - address-to-nodename translation in protocol-independent
     manner



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

     int
     getnameinfo(const struct sockaddr *sa, socklen_t salen, char *host,
             size_t hostlen, char *serv, size_t servlen, int flags);

DESCRIPTION
     The getnameinfo() function is defined for protocol-independent address-
     to-nodename translation.  Its functionality is a reverse conversion of
     getaddrinfo(3),  and implements similar functionality with
     gethostbyaddr(3)and  getservbyport(3) in more sophisticated manner.

     This function looks up an IP address and port number provided by the
     caller in the DNS and system-specific database, and returns text strings
     for both in buffers provided by the caller.  The function indicates suc-
     cessful completion by a zero return value; a non-zero return value indi-
     cates failure.

     The first argument, sa, points to either a sockaddr_in structure (for
     IPv4) or a sockaddr_in6 structure (for IPv6) that holds the IP address
     and port number.  The salen argument gives the length of the sockaddr_in
     or sockaddr_in6 structure.

     The function returns the nodename associated with the IP address in the
     buffer pointed to by the host argument.  The caller provides the size of
     this buffer via the hostlen argument.  The service name associated with
     the port number is returned in the buffer pointed to by serv, and the
     servlen argument gives the length of this buffer.  The caller specifies
     not to return either string by providing a zero value for the hostlen or
     servlen arguments.  Otherwise, the caller must provide buffers large
     enough to hold the nodename and the  service name, including the termi-
     nating null characters.

     Unfortunately most systems do not provide constants that specify the max-
     imum size of either a fully-qualified domain name or a service name.
     Therefore to aid the application in allocating buffers for these two re-
     turned strings the following constants are defined in <netdb.h>:

     #define NI_MAXHOST  1025
     #define NI_MAXSERV    32

     The first value is actually defined as the constant MAXDNAME in recent
     versions of BIND's <arpa/nameser.h> header (older versions of BIND define
     this constant to be 256) and the second is a guess based on the services
     listed in the current Assigned Numbers RFC.

     The final argument is a flag that changes the default actions of this
     function.  By default the fully-qualified domain name (FQDN) for the host
     is looked up in the DNS and returned.  If the flag bit NI_NOFQDN is set,
     only the nodename portion of the FQDN is returned for local hosts.

     If the flag bit NI_NUMERICHOST is set, or if the host's name cannot be
     located in the DNS, the numeric form of the host's address is returned
     instead of its name (e.g., by calling inet_ntop() instead of
     getnodebyaddr()). If the flag bit NI_NAMEREQD is set, an error is re-
     turned if the host's name cannot be located in the DNS.

     If the flag bit NI_NUMERICSERV is set, the numeric form of the service
     address is returned (e.g., its port number) instead of its name.  The two
     NI_NUMERICxxx flags are required to support the -n flag that many com-
     mands provide.

     A fifth flag bit, NI_DGRAM, specifies that the service is a datagram ser-
     vice, and causes getservbyport() to be called with a second argument of
     "udp" instead of its default of "tcp". This is required for the few ports
     (512-514) that have different services for UDP and TCP.

     These NI_xxx flags are defined in <netdb.h>.

FILES
     /etc/hosts
     /etc/host.conf
     /etc/resolv.conf

DIAGNOSTICS
     The function indicates successful completion by a zero return value; a
     non-zero return value indicates failure.

SEE ALSO
     getaddrinfo(3),  gethostbyaddr(3),  getservbyport(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                                2