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getnameinfo !!!getnameinfo NAME SYNOPSIS DESCRIPTION RETURN VALUE ERRORS FILES NOTE EXAMPLES CONFORMING TO SEE ALSO ---- !!NAME getnameinfo - address-to-name translation in protocol-independent manner !!SYNOPSIS __#include __''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 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'' repectively) 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, '''' defines the constants # define NI_MAXHOST 1025 # define NI_MAXSERV 32 The former is the constant MAXDNAME in recent versions of BIND's '''' 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- 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- !!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'', internet draft, work in progress. ftp://ftp.ietf.org/internet-drafts/draft-ietf-ipngwg-scopedaddr-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/publications/library/proceedings/usenix2000/freenix/metzprotocol.html ----
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