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GETNAMEINFO(3P)            POSIX Programmer's Manual           GETNAMEINFO(3P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       getnameinfo - get name information

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

       int getnameinfo(const struct sockaddr *restrict sa, socklen_t salen,
              char *restrict node, socklen_t nodelen, char *restrict service,
              socklen_t servicelen, int flags);


DESCRIPTION
       The  getnameinfo()  function shall translate a socket address to a node name and service location, all of which
       are defined as in getaddrinfo().

       The sa argument points to a socket address structure to be translated.

       If the socket address structure contains an IPv4-mapped IPv6 address or an IPv4-compatible  IPv6  address,  the
       implementation shall extract the embedded IPv4 address and lookup the node name for that IPv4 address.

       Note:  The  IPv6  unspecified  address ( "::" ) and the IPv6 loopback address ( "::1" ) are not IPv4-compatible
              addresses. If the address is the IPv6 unspecified address ( "::" ), a lookup is not performed,  and  the
              [EAI_NONAME] error is returned.


       If  the  node  argument  is  non-NULL  and the nodelen argument is non-zero, then the node argument points to a
       buffer able to contain up to nodelen characters that receives the node name as a null-terminated string. If the
       node  argument is NULL or the nodelen argument is zero, the node name shall not be returned. If the node's name
       cannot be located, the numeric form of the address contained in the socket address structure pointed to by  the
       sa argument is returned instead of its name.

       If  the  service argument is non-NULL and the servicelen argument is non-zero, then the service argument points
       to a buffer able to contain up to servicelen bytes that receives the service name as a null-terminated  string.
       If  the service argument is NULL or the servicelen argument is zero, the service name shall not be returned. If
       the service's name cannot be located, the numeric form of the service address (for example,  its  port  number)
       shall be returned instead of its name.

       The  flags  argument is a flag that changes the default actions of the function. By default the fully-qualified
       domain name (FQDN) for the host shall be returned, but:

        * If the flag bit NI_NOFQDN is set, only the node name portion of the FQDN shall be returned for local  hosts.


        * If  the  flag  bit  NI_NUMERICHOST  is  set, the numeric form of the address contained in the socket address
          structure pointed to by the sa argument shall be returned instead of its name, under all circumstances.


        * If the flag bit NI_NAMEREQD is set, an error shall be returned if the host's name cannot be located.


        * If the flag bit NI_NUMERICSERV is set, the numeric form of the service address shall be returned (for  exam-
          ple, its port number) instead of its name, under all circumstances.


        * If  the  flag  bit  NI_NUMERICSCOPE  is set, the numeric form of the scope identifier shall be returned (for
          example, interface index) instead of its name. This flag shall be ignored if the sa argument is not an  IPv6
          address.


        * If  the  flag  bit  NI_DGRAM is set, this indicates that the service is a datagram service (SOCK_DGRAM). The
          default behavior shall assume that the service is a stream service (SOCK_STREAM).


       Notes:

               1. The two NI_NUMERICxxx flags are required to support the -n flag that many commands provide.


               2. The NI_DGRAM flag is required for the few AF_INET and AF_INET6 port numbers (for example, [512,514])
                  that represent different services for UDP and TCP.



       The getnameinfo() function shall be thread-safe.

RETURN VALUE
       A  zero return value for getnameinfo() indicates successful completion; a non-zero return value indicates fail-
       ure. The possible values for the failures are listed in the ERRORS section.

       Upon successful completion, getnameinfo() shall return the node and service names, if requested, in the buffers
       provided. The returned names are always null-terminated strings.

ERRORS
       The getnameinfo() function shall fail and return the corresponding value if:

       EAI_AGAIN
              The name could not be resolved at this time. Future attempts may succeed.

       EAI_BADFLAGS

              The flags had an invalid value.

       EAI_FAIL
              A non-recoverable error occurred.

       EAI_FAMILY
              The address family was not recognized or the address length was invalid for the specified family.

       EAI_MEMORY
              There was a memory allocation failure.

       EAI_NONAME
              The name does not resolve for the supplied parameters.

       NI_NAMEREQD is set and the host's name cannot be located, or both nodename and servname were null.

       EAI_OVERFLOW

              An  argument  buffer  overflowed. The buffer pointed to by the node argument or the service argument was
              too small.

       EAI_SYSTEM
              A system error occurred. The error code can be found in errno.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       If the returned values are to be used as part of any further name resolution (for  example,  passed  to  getad-
       drinfo()), applications should provide buffers large enough to store any result possible on the system.

       Given  the  IPv4-mapped  IPv6  address  "::ffff:1.2.3.4", the implementation performs a lookup as if the socket
       address structure contains the IPv4 address "1.2.3.4" .

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       gai_strerror(),  getaddrinfo(),  getservbyname(),  inet_ntop(),  socket(),  the  Base  Definitions  volume   of
       IEEE Std 1003.1-2001, <netdb.h>, <sys/socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  Issue  6,  Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The
       Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan-
       dard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                      GETNAMEINFO(3P)