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->GETNAMEINFO(3) System Library Functions Manual GETNAMEINFO(3)
-
-NAME
- getnameinfo - address-to-nodename translation in protocol-independent
- manner
-
-SYNOPSIS
- #include <sys/types.h>
- #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() function is defined for protocol-independent address-
- to-nodename translation. Its functionality is a reverse conversion of
- getaddrinfo(3), and implements similar functionality with
- gethostbyaddr(3) and getservbyport(3) in more sophisticated manner.
-
- This function looks up an IP address and port number provided by the
- caller in the DNS and system-specific database, and returns text strings
- for both in buffers provided by the caller. The function indicates suc-
- cessful completion by a zero return value; a non-zero return value indi-
- cates failure.
-
- The first argument, sa, points to either a sockaddr_in structure (for
- IPv4) or a sockaddr_in6 structure (for IPv6) that holds the IP address
- and port number. The salen argument gives the length of the sockaddr_in
- or sockaddr_in6 structure.
-
- The function returns the nodename associated with the IP address in the
- buffer pointed to by the host argument. The caller provides the size of
- this buffer via the hostlen argument. The service name associated with
- the port number is returned in the buffer pointed to by serv, and the
- servlen argument gives the length of this buffer. The caller specifies
- not to return either string by providing a zero value for the hostlen or
- servlen arguments. Otherwise, the caller must provide buffers large
- enough to hold the nodename and the service name, including the terminat-
- ing null characters.
-
- Unfortunately most systems do not provide constants that specify the max-
- imum size of either a fully-qualified domain name or a service name.
- Therefore to aid the application in allocating buffers for these two
- returned strings the following constants are defined in <netdb.h>:
-
- #define NI_MAXHOST MAXHOSTNAMELEN
- #define NI_MAXSERV 32
-
- The first value is actually defined as the constant MAXDNAME in recent
- versions of BIND's <arpa/nameser.h> header (older versions of BIND define
- this constant to be 256) and the second is a guess based on the services
- listed in the current Assigned Numbers RFC.
-
- The final argument is a flag that changes the default actions of this
- function. By default the fully-qualified domain name (FQDN) for the host
- is looked up in the DNS and returned. If the flag bit NI_NOFQDN is set,
- only the nodename portion of the FQDN is returned for local hosts.
-
- If the flag bit NI_NUMERICHOST is set, or if the host's name cannot be
- located in the DNS, the numeric form of the host's address is returned
- instead of its name (e.g., by calling inet_ntop() instead of
- gethostbyaddr()). If the flag bit NI_NAMEREQD is set, an error is
- returned if the host's name cannot be located in the DNS.
-
- If the flag bit NI_NUMERICSERV is set, the numeric form of the service
- address is returned (e.g., its port number) instead of its name. The two
- NI_NUMERICxxx flags are required to support the -n flag that many com-
- mands provide.
-
- A fifth flag bit, NI_DGRAM, specifies that the service is a datagram ser-
- vice, and causes getservbyport() 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 different services for UDP and TCP.
-
- These NI_xxx flags are defined in <netdb.h>.
-
- Extension for scoped IPv6 address
- The implementation allows experimental numeric IPv6 address notation with
- scope identifier. IPv6 link-local address will appear as string like
- ``fe80::1%ne0'', if NI_WITHSCOPEID bit is enabled in flags argument.
- Refer to getaddrinfo(3) for the notation.
-
-EXAMPLES
- The following code tries to get numeric hostname, and service name, for
- given socket address. Observe that there is no hardcoded reference to
- 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 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);
-
-DIAGNOSTICS
- The function indicates successful completion by a zero return value; a
- non-zero return value indicates failure. Error codes are as below:
-
- EAI_AGAIN The name could not be resolved at this time. Future
- attempts may succeed.
-
- EAI_BADFLAGS The flags had 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 There was a memory allocation failure.
-
- EAI_NONAME The name does not resolve for the supplied parameters.
- NI_NAMEREQD is set and the host's name cannot be
- located, or both nodename and servname were null.
-
- EAI_SYSTEM A system error occurred. The error code can be found
- in errno.
-
-SEE ALSO
- getaddrinfo(3), gethostbyaddr(3), getservbyport(3), hosts(5),
- resolv.conf(5), services(5), hostname(7), named(8)
-
- R. Gilligan, S. Thomson, J. Bound, and W. Stevens, Basic Socket Interface
- Extensions for IPv6, RFC2553, March 1999.
-
- Tatsuya Jinmei and Atsushi Onoe, An Extension of Format for IPv6 Scoped
- Addresses, internet draft, draft-ietf-ipngwg-scopedaddr-format-02.txt,
- work in progress material.
-
- Craig Metz, "Protocol Independence Using the Sockets API", Proceedings of
- the freenix track: 2000 USENIX annual technical conference, June 2000.
-
-HISTORY
- The implementation first appeared in WIDE Hydrangea IPv6 protocol stack
- kit.
-
-STANDARDS
- The getaddrinfo() function is defined IEEE POSIX 1003.1g draft specifica-
- tion, and documented in ``Basic Socket Interface Extensions for IPv6''
- (RFC2553).
-
-BUGS
- The current implementation is not thread-safe.
-
- The text was shamelessly copied from RFC2553.
-
- OpenBSD intentionally uses different NI_MAXHOST value from what RFC2553
- suggests, to avoid buffer length handling mistakes.
-
-BSD May 25, 1995 BSD
- </PRE
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