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RedHat 9 (Linux i386) - man page for getnameinfo (redhat section 3)

getnameinfo(3)			     UNIX Programmer's Manual			   getnameinfo(3)

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

SYNOPSIS
       #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
       The getnameinfo(3) function is defined for protocol-independent address-to-nodename trans-
       lation.	It combines the functionality of gethostbyaddr(3) and getservbyport(3) and is the
       inverse	of  getaddrinfo(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 respectively) 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
	      If set, return only the hostname part of the FQDN for local hosts.

       NI_NUMERICHOST
	      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
	      If set, then a error is returned if the hostname cannot be looked up.

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

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

       EAI_BADFLAGS
	      The flags parameter has 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
	      Out of memory.

       EAI_NONAME
	      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
	      A system error occurred. The error code can be found in errno.

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

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

SEE ALSO
       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 Interface Extensions for
       IPv6, RFC 2553, March 1999.

       Tatsuya Jinmei and Atsushi Onoe, An Extension of Format for IPv6 Scoped Addresses,  inter-
       net  draft, work in progress.  ftp://ftp.ietf.org/internet-drafts/draft-ietf-ipngwg-scope-
       daddr-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/publica-
       tions/library/proceedings/usenix2000/freenix/metzprotocol.html

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


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