getnameinfo

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



NAME
       getnameinfo  - address-to-name translation in protocol-independent man-
       ner

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  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 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 spec-
       ified 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  ser-
       vices 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 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/internet-drafts/draft-ietf-ipngwg-scopedaddr-for-
       mat-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)