lwres_getnameinfo(3) [centos man page]
LWRES_GETNAMEINFO(3) BIND9 LWRES_GETNAMEINFO(3) NAME
lwres_getnameinfo - lightweight resolver socket address structure to hostname and service name SYNOPSIS
#include <lwres/netdb.h> int lwres_getnameinfo(const struct sockaddr *sa, size_t salen, char *host, size_t hostlen, char *serv, size_t servlen, int flags); DESCRIPTION
This function is equivalent to the getnameinfo(3) function defined in RFC2133. lwres_getnameinfo() returns the hostname for the struct sockaddr sa which is salen bytes long. The hostname is of length hostlen and is returned via *host. The maximum length of the hostname is 1025 bytes: NI_MAXHOST. The name of the service associated with the port number in sa is returned in *serv. It is servlen bytes long. The maximum length of the service name is NI_MAXSERV - 32 bytes. The flags argument sets the following bits: 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(), instead of a host name. NI_NAMEREQD A name is required. If the hostname cannot be found in the DNS and this flag is set, a non-zero error code is returned. If the hostname is not found and the flag is not set, the address is returned in numeric form. 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() 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. RETURN VALUES
lwres_getnameinfo() returns 0 on success or a non-zero error code if an error occurs. SEE ALSO
RFC2133(), getservbyport(3), lwres(3), lwres_getnameinfo(3), lwres_getnamebyaddr(3). lwres_net_ntop(3). BUGS
RFC2133 fails to define what the nonzero return values of getnameinfo(3) are. COPYRIGHT
Copyright (C) 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC") Copyright (C) 2000, 2001 Internet Software Consortium. BIND9 Jun 30, 2000 LWRES_GETNAMEINFO(3)
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getnameinfo(3) UNIX Programmer's Manual getnameinfo(3) NAME
getnameinfo - address-to-name translation in protocol-independent manner 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 gethost- byaddr(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 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 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 host- name 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 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 refer- ence 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 ", 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 ", 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 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 Linux Man Page 2000-12-11 getnameinfo(3)