getnameinfo

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 freeaddrinfo().

       The sa argument points to a socket address structure to be translated.
       The salen argument contains the length of the address pointed to by sa.

       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.

       If the address is the IPv6 unspecified address ("::"), a lookup shall not
       be performed and the behavior shall be the same as when the node's name
       cannot be located.

       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
       bytes 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.

        *  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 example, its port number)
           instead of its name.

        *  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 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 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 getaddrinfo()), 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".

       The IPv6 unspecified address ("::") and the IPv6 loopback address ("::1")
       are not IPv4-compatible addresses.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       endservent(), freeaddrinfo(), gai_strerror(), inet_ntop(), socket()

       The Base Definitions volume of POSIX.1‐2008, <netdb.h>, <sys_socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical
       and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008
       with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most
       likely to have been introduced during the conversion of the source files
       to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                   2013                       GETNAMEINFO(3P)