getnameinfo(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       getnameinfo — get name information

SYNOPSIS         top

       #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         top

       The getnameinfo() function shall translate a socket address to a
       node name and service location, all of which are defined as in
       freeaddrinfo(3p).

       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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       endservent(3p), freeaddrinfo(3p), gai_strerror(3p),
       inet_ntop(3p), socket(3p)

       The Base Definitions volume of POSIX.1‐2017, netdb.h(0p),
       sys_socket.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                   GETNAMEINFO(3P)

Pages that refer to this page: netdb.h(0p)freeaddrinfo(3p)