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+.\" $OpenBSD: getnameinfo.3,v 1.30 2004/12/20 22:15:29 millert Exp $
+.\"
+.\" Copyright (C) 2004 Internet Systems Consortium, Inc. ("ISC")
+.\" Copyright (C) 2000, 2001 Internet Software Consortium.
+.\"
+.\" Permission to use, copy, modify, and distribute this software for any
+.\" purpose with or without fee is hereby granted, provided that the above
+.\" copyright notice and this permission notice appear in all copies.
+.\"
+.\" THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
+.\" REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+.\" AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
+.\" INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+.\" LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+.\" OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+.\" PERFORMANCE OF THIS SOFTWARE.
+.\"
+.Dd December 20, 2004
+.Dt GETNAMEINFO 3
+.Os
+.Sh NAME
+.Nm getnameinfo
+.Nd socket address structure to hostname and service name
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/socket.h>
+.Fd #include <netdb.h>
+.Ft int
+.Fn getnameinfo "const struct sockaddr *sa" "socklen_t salen" "char *host" "size_t hostlen" "char *serv" "size_t servlen" "int flags"
+.Sh DESCRIPTION
+The
+.Fn getnameinfo
+function is used to convert a
+.Li sockaddr
+structure to a pair of host name and service strings.
+It is a replacement for and provides more flexibility than the
+.Xr gethostbyaddr 3
+and
+.Xr getservbyport 3
+functions and is the converse of the
+.Xr getaddrinfo 3
+function.
+.Pp
+The
+.Li sockaddr
+structure
+.Fa sa
+should point to either a
+.Li sockaddr_in
+or
+.Li sockaddr_in6
+structure (for IPv4 or IPv6 respectively) that is
+.Fa salen
+bytes long.
+.Pp
+The host and service names associated with
+.Fa sa
+are stored in
+.Fa host
+and
+.Fa serv
+which have size parameters
+.Fa hostlen
+and
+.Fa servlen .
+The maximum value for
+.Fa hostlen
+is
+.Dv NI_MAXHOST
+and
+the maximum value for
+.Fa servlen
+is
+.Dv NI_MAXSERV
+- 32,
+as defined by
+.Aq Pa netdb.h .
+.Pp
+The
+.Fa flags
+argument is formed by
+.Tn OR Ns 'ing
+the following values:
+.Bl -tag -width "NI_NUMERICHOSTXX"
+.It Dv NI_NOFQDN
+A fully qualified domain name is not required for local hosts.
+The local part of the fully qualified domain name is returned instead.
+.It Dv NI_NUMERICHOST
+Return the address in numeric form, as if calling
+.Xr inet_ntop 3 ,
+instead of a host name.
+.It Dv NI_NAMEREQD
+A name is required.
+If the host name cannot be found in DNS and this flag is set,
+a non-zero error code is returned.
+If the host name is not found and the flag is not set, the
+address is returned in numeric form.
+.It NI_NUMERICSERV
+The service name is returned as a digit string representing the port number.
+.It NI_DGRAM
+Specifies that the service being looked up is a datagram
+service, and causes
+.Xr getservbyport 3
+to be called with a second argument of
+.Dq udp
+instead of its default of
+.Dq tcp .
+This is required for the few ports (512-514) that have different services
+for
+.Tn UDP
+and
+.Tn TCP .
+.Sh RETURN VALUES
+.Fn getnameinfo
+returns zero on success or one of the error codes listed in
+.Xr gai_strerror 3
+if an error occurs.
+.Sh SEE ALSO
+.Xr inet_ntop 3 ,
+.Xr gai_strerror 3 ,
+.Xr getaddrinfo 3 ,
+.Xr gethostbyaddr 3 ,
+.Xr getservbyport 3 ,
+.Xr resolver 3 ,
+.Xr hosts 5 ,
+.Xr resolv.conf 5 ,
+.Xr services 5 ,
+.Xr hostname 7 ,
+.Xr named 8
+.Rs
+.%A R. Gilligan
+.%A S. Thomson
+.%A J. Bound
+.%A W. Stevens
+.%T Basic Socket Interface Extensions for IPv6
+.%R RFC 2553
+.%D March 1999
+.Re
+.Rs
+.%A Tatsuya Jinmei
+.%A Atsushi Onoe
+.%T "An Extension of Format for IPv6 Scoped Addresses"
+.%R internet draft
+.%N draft-ietf-ipngwg-scopedaddr-format-02.txt
+.%O work in progress material
+.Re
+.Rs
+.%A Craig Metz
+.%T Protocol Independence Using the Sockets API
+.%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
+.%D June 2000
+.Re
+.Sh STANDARDS
+The
+.Fn getnameinfo
+function is defined by the
+.St -p1003.1g-2000
+draft specification and documented in
+.Tn "RFC 2553" ,
+.Dq Basic Socket Interface Extensions for IPv6 .
+.Sh BUGS
+Due to the use of dynamic allocation,
+.Fn getaddrinfo
+is not thread-safe.
+.Pp
+.Ox
+intentionally uses a different
+.Dv NI_MAXHOST
+value from what
+.Tn "RFC 2553"
+suggests, to avoid buffer length handling mistakes.