getnameinfo(3) - NetBSD Manual Pages

GETNAMEINFO(3)          NetBSD Library Functions Manual         GETNAMEINFO(3)


NAME

     getnameinfo -- socket address structure to hostname and service name


SYNOPSIS

     #include <netdb.h>

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


DESCRIPTION

     The getnameinfo() function is used to convert a sockaddr structure to a
     pair of host name and service strings.  It is a replacement for and pro-
     vides more flexibility than the gethostbyaddr(3) and getservbyport(3)
     functions and is the converse of the getaddrinfo(3) function.

     The sockaddr structure sa should point to a sockaddr_in (for IPv4),
     sockaddr_in6 (for IPv6), sockaddr_atalk (for AppleTalk), sockaddr_link
     (for link layer), or sockaddr_local (for local/unix) structures that are
     salen bytes long.

     The host and service names associated with sa are stored in host and serv
     which have length parameters hostlen and servlen.  The maximum value for
     hostlen is NI_MAXHOST and the maximum value for servlen is NI_MAXSERV, as
     defined by <netdb.h>.  If a length parameter is zero, no string will be
     stored.  Otherwise, enough space must be provided to store the host name
     or service string plus a byte for the NUL terminator.

     The flags argument is formed by or'ing the following values:

     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.

     NI_NUMERICHOST
                   Return the address in numeric form, as if calling
                   inet_ntop(3), instead of a host name.

     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.

     NI_NUMERICSCOPE
                   For IPv6 addresses the numeric form of the IPv6 scope iden-
                   tifier is returned.  This flag is ignored for non-IPv6
                   addresses.

     NI_NUMERICSERV
                   The service name is returned as a digit string representing
                   the port number.

     NI_DGRAM      Specifies that the service being looked up is a datagram
                   service, and causes getservbyport(3) to be called with a
                   second argument of "udp" instead of its default of "tcp".
                   This is required for the few ports (512-514) that have dif-
                   ferent services for UDP and TCP.

     This implementation allows numeric IPv6 address notation with scope iden-
     tifier, as documented in chapter 11 of draft-ietf-ipv6-scoping-
     arch-02.txt.  IPv6 link-local address will appear as a string like
     `fe80::1%ne0'.  Refer to getaddrinfo(3) for more information.


RETURN VALUES

     getnameinfo() returns zero on success or one of the error codes listed in
     gai_strerror(3) if an error occurs.


EXAMPLES

     The following code tries to get a numeric host name, and service name,
     for a given socket address.  Observe 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)) {
                   errx(1, "could not get numeric hostname");
                   /*NOTREACHED*/
           }
           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)) {
                   errx(1, "could not resolve hostname");
                   /*NOTREACHED*/
           }
           printf("host=%s\n", hbuf);


SEE ALSO

     gai_strerror(3), getaddrinfo(3), gethostbyaddr(3), getservbyport(3),
     inet_ntop(3), resolver(3), hosts(5), resolv.conf(5), services(5),
     hostname(7)<