lwres_getipnodebyname, lwres_getipnodebyaddr, lwres_freehostent — lightweight resolver nodename / address translation API
#include <lwres/netdb.h>
struct hostent *
lwres_getipnodebyname( |
const char *name, |
| int af, | |
| int flags, | |
int *error_num); |
struct hostent *
lwres_getipnodebyaddr( |
const void *src, |
| size_t len, | |
| int af, | |
int *error_num); |
void
lwres_freehostent( |
struct hostent *he); |
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_nameThe official (canonical) name of the host.
h_aliasesA NULL-terminated array of alternate names (nicknames) for the host.
h_addrtypeThe type of address being returned - usually PF_INET or PF_INET6.
h_lengthThe length of the address in bytes.
h_addr_listA 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_ADDRCONFIGOnly 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.
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_FOUNDNo such host is known.
NO_ADDRESSThe 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_AGAINA temporary and possibly transient error occurred, such as a failure of a server to respond. The request may succeed if retried.
NO_RECOVERYAn unexpected failure occurred, and retrying the request is pointless.
lwres_hstrerror(3) translates these error codes to suitable error messages.