LWRES_GETIPNODE
NAME
lwres_getipnodebyname, lwres_getipnodebyaddr, lwres_freehostent - lightweight resolver nodename / address translation API
SYNOPSIS
I struct hostent * lwres_getipnodebyname(const char * name , int af , int flags , int * error_num );
I struct hostent * lwres_getipnodebyaddr(const void * src , size_t len , int af , int * error_num );
I void lwres_freehostent(struct hostent * he );
DESCRIPTION
These functions perform thread safe, protocol independent nodename-to-address and address-to-nodename translation as defined in RFC2553.
They use a
struct hostent
which is defined in
namedb.h:
struct hostent {
char *h_name; /* official name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses from name server */
};
#define h_addr h_addr_list[0] /* address, for backward compatibility */
The members of this structure are:
h_name
The official (canonical) name of the host.
h_aliases
A NULL-terminated array of alternate names (nicknames) for the host.
h_addrtype
The type of address being returned - usually
PF_INET
or
PF_INET6.
h_length
The length of the address in bytes.
h_addr_list
A
NULL
terminated array of network addresses for the host. Host addresses are returned in network byte order.
lwres_getipnodebyname()
looks up addresses of protocol family
af
for the hostname
name. The
flags
parameter contains ORed flag bits to specify the types of addresses that are searched for, and the types of addresses that are returned. The flag bits are:
AI_V4MAPPED
This is used with an
af
of AF_INET6, and causes IPv4 addresses to be returned as IPv4-mapped IPv6 addresses.
AI_ALL
This is used with an
af
of AF_INET6, and causes all known addresses (IPv6 and IPv4) to be returned. If AI_V4MAPPED is also set, the IPv4 addresses are return as mapped IPv6 addresses.
AI_ADDRCONFIG
Only return an IPv6 or IPv4 address if here is an active network interface of that type. This is not currently implemented in the BIND 9 lightweight resolver, and the flag is ignored.
AI_DEFAULT
This default sets the
AI_V4MAPPED
and
AI_ADDRCONFIG
flag bits.
lwres_getipnodebyaddr()
performs a reverse lookup of address
src
which is
len
bytes long.
af
denotes the protocol family, typically
PF_INET
or
PF_INET6.
lwres_freehostent()
releases all the memory associated with the
struct hostent
pointer
he. Any memory allocated for the
h_name,
h_addr_list
and
h_aliases
is freed, as is the memory for the
hostent
structure itself.
RETURN VALUES
If an error occurs,
lwres_getipnodebyname()
and
lwres_getipnodebyaddr()
set
*error_num
to an appropriate error code and the function returns a
NULL
pointer. The error codes and their meanings are defined in
<lwres/netdb.h>:
HOST_NOT_FOUND
No such host is known.
NO_ADDRESS
The server recognised the request and the name but no address is available. Another type of request to the name server for the domain might return an answer.
TRY_AGAIN
A temporary and possibly transient error occurred, such as a failure of a server to respond. The request may succeed if retried.
NO_RECOVERY
An unexpected failure occurred, and retrying the request is pointless.
lwres_hstrerror(3)
translates these error codes to suitable error messages.
SEE ALSO
RFC2553(),
lwres(3),
lwres_gethostent(3),
lwres_getaddrinfo(3),
lwres_getnameinfo(3),
lwres_hstrerror(3).
COPYRIGHT
Copyright 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC")
Copyright 2000, 2001, 2003 Internet Software Consortium.
