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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 differ (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 getad-
       drinfo().
       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  exam-
       ple, 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 circum-
          stances.
        * 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  ser-
          vice  address  shall  be  returned  (for  example,  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 repre-
                  sent 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 failure. 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 node-
       name 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 reso-
       lution (for example, passed to getaddrinfo()), applications should pro-
       vide 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, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications 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 Standard, 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)