1.\" $NetBSD: getnameinfo.3,v 1.16 2001/11/15 06:46:33 itojun Exp $ 2.\" $KAME: getnameinfo.3,v 1.20 2001/01/05 13:37:37 itojun Exp $ 3.\" 4.\" Copyright (c) 1983, 1987, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" From: @(#)gethostbyname.3 8.4 (Berkeley) 5/25/95 36.\" 37.Dd May 25, 1995 38.Dt GETNAMEINFO 3 39.Os 40.\" 41.Sh NAME 42.Nm getnameinfo 43.Nd address-to-nodename translation in protocol-independent manner 44.\" 45.Sh LIBRARY 46.Lb libc 47.\" 48.Sh SYNOPSIS 49.Fd #include <sys/types.h> 50.Fd #include <sys/socket.h> 51.Fd #include <netdb.h> 52.Ft int 53.Fn getnameinfo "const struct sockaddr *sa" "socklen_t salen" \ 54"char *host" "size_t hostlen" "char *serv" "size_t servlen" "int flags" 55.\" 56.Sh DESCRIPTION 57The 58.Fn getnameinfo 59function is defined for protocol-independent address-to-nodename translation. 60Its functionality is a reverse conversion of 61.Xr getaddrinfo 3 , 62and implements similar functionality with 63.Xr gethostbyaddr 3 64and 65.Xr getservbyport 3 66in more sophisticated manner. 67.Pp 68This function looks up an IP address and port number provided by the 69caller in the DNS and system-specific database, and returns text 70strings for both in buffers provided by the caller. 71The function indicates successful completion by a zero return value; 72a non-zero return value indicates failure. 73.Pp 74The first argument, 75.Fa sa , 76points to either a 77.Li sockaddr_in 78structure (for IPv4) or a 79.Li sockaddr_in6 80structure (for IPv6) that holds the IP address and port number. 81The 82.Fa salen 83argument gives the length of the 84.Li sockaddr_in 85or 86.Li sockaddr_in6 87structure. 88.Pp 89The function returns the nodename associated with the IP address in 90the buffer pointed to by the 91.Fa host 92argument. 93The caller provides the size of this buffer via the 94.Fa hostlen 95argument. 96The service name associated with the port number is returned in the buffer 97pointed to by 98.Fa serv , 99and the 100.Fa servlen 101argument gives the length of this buffer. 102The caller specifies not to return either string by providing a zero 103value for the 104.Fa hostlen 105or 106.Fa servlen 107arguments. 108Otherwise, the caller must provide buffers large enough to hold the 109nodename and the service name, including the terminating null characters. 110.Pp 111Unfortunately most systems do not provide constants that specify the 112maximum size of either a fully-qualified domain name or a service name. 113Therefore to aid the application in allocating buffers for these two 114returned strings the following constants are defined in 115.Aq Pa netdb.h : 116.Bd -literal -offset 117#define NI_MAXHOST 1025 118#define NI_MAXSERV 32 119.Ed 120.Pp 121The first value is actually defined as the constant 122.Dv MAXDNAME 123in recent versions of BIND's 124.Aq Pa arpa/nameser.h 125header 126.Po 127older versions of BIND define this constant to be 256 128.Pc 129and the second is a guess based on the services listed in the current 130Assigned Numbers RFC. 131.Pp 132The final argument is a 133.Fa flag 134that changes the default actions of this function. 135By default the fully-qualified domain name (FQDN) for the host is 136looked up in the DNS and returned. 137If the flag bit 138.Dv NI_NOFQDN 139is set, only the nodename portion of the FQDN is returned for local hosts. 140.Pp 141If the 142.Fa flag 143bit 144.Dv NI_NUMERICHOST 145is set, or if the host's name cannot be located in the DNS, 146the numeric form of the host's address is returned instead of its name 147.Po 148e.g., by calling 149.Fn inet_ntop 150instead of 151.Fn gethostbyaddr 152.Pc . 153If the 154.Fa flag 155bit 156.Dv NI_NAMEREQD 157is set, an error is returned if the host's name cannot be located in the DNS. 158.Pp 159If the flag bit 160.Dv NI_NUMERICSERV 161is set, the numeric form of the service address is returned 162.Pq e.g., its port number 163instead of its name. 164The two 165.Dv NI_NUMERICxxx 166flags are required to support the 167.Fl n 168flag that many commands provide. 169.Pp 170A fifth flag bit, 171.Dv NI_DGRAM , 172specifies that the service is a datagram service, and causes 173.Fn getservbyport 174to be called with a second argument of 175.Dq udp 176instead of its default of 177.Dq tcp . 178This is required for the few ports (512-514) 179that have different services for UDP and TCP. 180.Pp 181These 182.Dv NI_xxx 183flags are defined in 184.Aq Pa netdb.h . 185.\" 186.Ss Extension for scoped IPv6 address 187The implementation allows experimental numeric IPv6 address notation with 188scope identifier. 189IPv6 link-local address will appear as string like 190.Dq Li fe80::1%ne0 . 191Refer to 192.Xr getaddrinfo 3 193for the notation. 194.\" 195.Sh EXAMPLES 196The following code tries to get numeric hostname, and service name, 197for given socket address. 198Observe that there is no hardcoded reference to particular address family. 199.Bd -literal -offset indent 200struct sockaddr *sa; /* input */ 201char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV]; 202 203if (getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf), sbuf, 204 sizeof(sbuf), NI_NUMERICHOST | NI_NUMERICSERV)) { 205 errx(1, "could not get numeric hostname"); 206 /*NOTREACHED*/ 207} 208printf("host=%s, serv=%s\\n", hbuf, sbuf); 209.Ed 210.Pp 211The following version checks if the socket address has reverse address mapping. 212.Bd -literal -offset indent 213struct sockaddr *sa; /* input */ 214char hbuf[NI_MAXHOST]; 215 216if (getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf), NULL, 0, 217 NI_NAMEREQD)) { 218 errx(1, "could not resolve hostname"); 219 /*NOTREACHED*/ 220} 221printf("host=%s\\n", hbuf); 222.Ed 223.\" 224.Sh DIAGNOSTICS 225The function indicates successful completion by a zero return value; 226a non-zero return value indicates failure. 227Error codes are as below: 228.Bl -tag -width Er 229.It Dv EAI_AGAIN 230The name could not be resolved at this time. 231Future attempts may succeed. 232.It Dv EAI_BADFLAGS 233The flags had an invalid value. 234.It Dv EAI_FAIL 235A non-recoverable error occurred. 236.It Dv EAI_FAMILY 237The address family was not recognized or the address length was invalid 238for the specified family. 239.It Dv EAI_MEMORY 240There was a memory allocation failure. 241.It Dv EAI_NONAME 242The name does not resolve for the supplied parameters. 243.Dv NI_NAMEREQD 244is set and the host's name cannot be located, 245or both nodename and servname were null. 246.It Dv EAI_SYSTEM 247A system error occurred. 248The error code can be found in errno. 249.El 250.\" 251.Sh SEE ALSO 252.Xr getaddrinfo 3 , 253.Xr gethostbyaddr 3 , 254.Xr getservbyport 3 , 255.Xr hosts 5 , 256.Xr resolv.conf 5 , 257.Xr services 5 , 258.Xr hostname 7 , 259.Xr named 8 260.Pp 261.Rs 262.%A R. Gilligan 263.%A S. Thomson 264.%A J. Bound 265.%A W. Stevens 266.%T Basic Socket Interface Extensions for IPv6 267.%R RFC2553 268.%D March 1999 269.Re 270.Rs 271.%A Tatsuya Jinmei 272.%A Atsushi Onoe 273.%T "An Extension of Format for IPv6 Scoped Addresses" 274.%R internet draft 275.%N draft-ietf-ipngwg-scopedaddr-format-02.txt 276.%O work in progress material 277.Re 278.Rs 279.%A Craig Metz 280.%T Protocol Independence Using the Sockets API 281.%B "Proceedings of the freenix track: 2000 USENIX annual technical conference" 282.%D June 2000 283.Re 284.\" 285.Sh STANDARDS 286The 287.Fn getnameinfo 288function is defined IEEE POSIX 1003.1g draft specification, 289and documented in 290.Dq Basic Socket Interface Extensions for IPv6 291.Pq RFC2553 . 292.\" 293.Sh HISTORY 294The implementation first appeared in WIDE Hydrangea IPv6 protocol stack kit. 295.\" 296.Sh BUGS 297The current implementation is not thread-safe. 298.Pp 299The text was shamelessly copied from RFC2553. 300