NAME    [Toc]    [Back]

       getnameinfo  - address-to-name translation in protocol-independent manner

SYNOPSIS    [Toc]    [Back]

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

       int getnameinfo(const struct sockaddr *sa, socklen_t salen,
		       char *host, size_t hostlen,
		       char *serv, size_t servlen, int flags);

DESCRIPTION    [Toc]    [Back]

       The  getnameinfo(3)  function  is  defined   for   protocol-independent
       address-to-nodename  translation.   It  combines  the  functionality of
       gethostbyaddr(3) and getservbyport(3) and  is  the  inverse  of	getad-
       drinfo(3).   The  sa  argument is a pointer to a generic socket address
       structure (of type sockaddr_in or  sockaddr_in6)  of  size  salen  that
       holds  the  input  IP  address and port number.	The arguments host and
       serv are pointers to buffers (of size hostlen and servlen  repectively)
       to hold the return values.

       The  caller  can  specify  that	no  hostname  (or  no service name) is
       required by providing a NULL host (or serv) argument or a zero  hostlen
       (or  servlen)  parameter.  However, at least one of hostname or service
       name must be requested.

       The flags argument modifies the behaviour of getnameinfo(3) as follows:

       NI_NOFQDN    [Toc]    [Back]
	      If  set,	return	only  the  hostname part of the FQDN for local
	      hosts.

       NI_NUMERICHOST    [Toc]    [Back]
	      If set, then the numeric	form  of  the  hostname  is  returned.
	      (When  not  set,	this will still happen in case the node's name
	      cannot be looked up.)

       NI_NAMEREQD    [Toc]    [Back]
	      If set, then a error is  returned  if  the  hostname  cannot  be
	      looked up.

       NI_NUMERICSERV    [Toc]    [Back]
	      If  set,	then  the service address is returned in numeric form,
	      for example by its port number.

       NI_DGRAM    [Toc]    [Back]
	      If set, then the service is datagram  (UDP)  based  rather  than
	      stream (TCP) based. This is required for the few ports (512-514)
	      that have different services for UDP and TCP.

RETURN VALUE    [Toc]    [Back]

       On success 0 is returned, and node and service names, if requested, are
       filled with NUL-terminated strings, possibly truncated to fit the specified
 buffer lengths.  On error a nonzero value is returned, and  errno
       is set appropriately.

ERRORS    [Toc]    [Back]

       EAI_AGAIN
	      The name could not be resolved at this time. Try again later.

       EAI_BADFLAGS    [Toc]    [Back]
	      The flags parameter has an invalid value.

       EAI_FAIL    [Toc]    [Back]
	      A non-recoverable error occurred.

       EAI_FAMILY    [Toc]    [Back]
	      The address family was not recognized, or the address length was
	      invalid for the specified family.

       EAI_MEMORY    [Toc]    [Back]
	      Out of memory.

       EAI_NONAME    [Toc]    [Back]
	      The  name  does  not  resolve  for  the	supplied   parameters.
	      NI_NAMEREQD  is  set  and  the host's name cannot be located, or
	      neither hostname nor service name were requested.

       EAI_SYSTEM    [Toc]    [Back]
	      A system error occurred. The error code can be found in errno.

FILES    [Toc]    [Back]

       /etc/hosts
       /etc/nsswitch.conf
       /etc/resolv.conf

NOTE    [Toc]    [Back]

       In order to assist the programmer in choosing reasonable sizes for  the
       supplied buffers, <netdb.h> defines the constants
	      # define NI_MAXHOST      1025
	      # define NI_MAXSERV      32
       The  former  is	the  constant  MAXDNAME  in  recent versions of BIND's
       <arpa/nameser.h> header file. The latter is a guess based on  the  services
 listed in the current Assigned Numbers RFC.

EXAMPLES    [Toc]    [Back]

       The  following code tries to get the numeric hostname and service name,
       for a given socket address. Note that there is no  hardcoded  reference
       to a particular address family.

		struct sockaddr *sa;	/* input */
		char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];

		if (getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf), sbuf,
		    sizeof(sbuf), NI_NUMERICHOST | NI_NUMERICSERV) == 0)
			printf("host=%s, serv=%s\n", hbuf, sbuf);

       The  following  version	checks	if  the  socket  address has a reverse
       address mapping.

		struct sockaddr *sa;	/* input */
		char hbuf[NI_MAXHOST];

		if (getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf),
		    NULL, 0, NI_NAMEREQD))
		       printf("could not resolve hostname");
		else
		       printf("host=%s\n", hbuf);

CONFORMING TO    [Toc]    [Back]

       RFC 2553. (See also XNS, issue 5.2.)

SEE ALSO    [Toc]    [Back]

       getaddrinfo(3), gethostbyaddr(3),  getservbyname(3),  getservbyport(3),
       inet_ntop(3), socket(3), hosts(5), services(5), hostname(7), named(8)

       R.  Gilligan,  S. Thomson, J. Bound and W. Stevens, Basic Socket Inter-
       face Extensions for IPv6, RFC 2553, March 1999.

       Tatsuya Jinmei and Atsushi Onoe, An Extension of Format for IPv6 Scoped
       Addresses, internet draft, work in progress.  ftp://ftp.ietf.org/inter-
       net-drafts/draft-ietf-ipngwg-scopedaddr-format-02.txt

       Craig Metz, Protocol Independence Using the Sockets API, Proceedings of
       the  freenix track: 2000 USENIX annual technical conference, June 2000.
       http://www.usenix.org/publications/library/proceed-
       ings/usenix2000/freenix/metzprotocol.html



Linux Man Page			  2000-12-11			getnameinfo(3)