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LWRES_GETHOSTENT(3)
NAME
lwres_gethostbyname, lwres_gethostbyname2, lwres_gethostbyaddr,
lwres_gethostent, lwres_sethostent, lwres_endhostent,
lwres_gethostbyname_r, lwres_gethostbyaddr_r, lwres_gethostent_r,
lwres_sethostent_r, lwres_endhostent_r - lightweight resolver get network
host entry
SYNOPSIS
#include <lwres/netdb.h>
struct hostent * lwres_gethostbyname(const char *name);
struct hostent * lwres_gethostbyname2(const char *name, int af);
struct hostent * lwres_gethostbyaddr(const char *addr, int len, int type);
struct hostent * lwres_gethostent(void);
void lwres_sethostent(int stayopen);
void lwres_endhostent(void);
struct hostent * lwres_gethostbyname_r(const char *name, struct hostent
*resbuf, char *buf, int buflen, int *error);
struct hostent * lwres_gethostbyaddr_r(const char *addr, int len, int type,
struct hostent *resbuf, char *buf, int buflen, int *error);
struct hostent * lwres_gethostent_r(struct hostent *resbuf, char *buf, int
buflen, int *error);
void lwres_sethostent_r(int stayopen);
void lwres_endhostent_r(void);
DESCRIPTION
These functions provide hostname-to-address and address-to-hostname lookups
by means of the lightweight resolver. They are similar to the standard
gethostent(3) functions provided by most operating systems. They use a
struct hostent which is usually 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 - 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.
For backward compatibility with very old software, h_addr is the first
address in h_addr_list.
lwres_gethostent(), lwres_sethostent(), lwres_endhostent(),
lwres_gethostent_r(), lwres_sethostent_r() and lwres_endhostent_r() provide
iteration over the known host entries on systems that provide such
functionality through facilities like /etc/hosts or NIS. The lightweight
resolver does not currently implement these functions; it only provides
them as stub functions that always return failure.
lwres_gethostbyname() and lwres_gethostbyname2() look up the hostname name.
lwres_gethostbyname() always looks for an IPv4 address while
lwres_gethostbyname2() looks for an address of protocol family af: either
PF_INET or PF_INET6 - IPv4 or IPV6 addresses respectively. Successful calls
of the functions return a struct hostentfor the name that was looked up.
NULL is returned if the lookups by lwres_gethostbyname() or
lwres_gethostbyname2() fail.
Reverse lookups of addresses are performed by lwres_gethostbyaddr(). addr
is an address of length len bytes and protocol family type - PF_INET or
PF_INET6. lwres_gethostbyname_r() is a thread-safe function for forward
lookups. If an error occurs, an error code is returned in *error. resbuf
is a pointer to a struct hostent which is initialised by a successful call
to lwres_gethostbyname_r() . buf is a buffer of length len bytes which is
used to store the h_name, h_aliases, and h_addr_list elements of the struct
hostent returned in resbuf. Successful calls to lwres_gethostbyname_r()
return resbuf, which is a pointer to the struct hostent it created.
lwres_gethostbyaddr_r() is a thread-safe function that performs a reverse
lookup of address addr which is len bytes long and is of protocol family
type - PF_INET or PF_INET6. If an error occurs, the error code is returned
in *error. The other function parameters are identical to those in
lwres_gethostbyname_r(). resbuf is a pointer to a struct hostent which is
initialised by a successful call to lwres_gethostbyaddr_r(). buf is a
buffer of length len bytes which is used to store the h_name, h_aliases,
and h_addr_list elements of the struct hostent returned in resbuf.
Successful calls to lwres_gethostbyaddr_r() return resbuf, which is a
pointer to the struct hostent() it created.
RETURN VALUES
The functions lwres_gethostbyname(), lwres_gethostbyname2(),
lwres_gethostbyaddr(), and lwres_gethostent() return NULL to indicate an
error. In this case the global variable lwres_h_errno will contain one of
the following error codes defined in <lwres/netdb.h>:
HOST_NOT_FOUND
The host or address was not found.
TRY_AGAIN
A recoverable error occurred, e.g., a timeout. Retrying the lookup
may succeed.
NO_RECOVERY
A non-recoverable error occurred.
NO_DATA
The name exists, but has no address information associated with it (or
vice versa in the case of a reverse lookup). The code NO_ADDRESS is
accepted as a synonym for NO_DATA for backwards compatibility.
lwres_hstrerror(3) translates these error codes to suitable error messages.
lwres_gethostent() and lwres_gethostent_r() always return NULL.
Successful calls to lwres_gethostbyname_r() and lwres_gethostbyaddr_r()
return resbuf, a pointer to the struct hostent that was initialised by
these functions. They return NULL if the lookups fail or if buf was too
small to hold the list of addresses and names referenced by the h_name,
h_aliases, and h_addr_list elements of the struct hostent. If buf was too
small, both lwres_gethostbyname_r() and lwres_gethostbyaddr_r() set the
global variable errno to ERANGE.
SEE ALSO
gethostent(3), lwres_getipnode(3), lwres_hstrerror(3)
BUGS
lwres_gethostbyname(), lwres_gethostbyname2(), lwres_gethostbyaddr() and
lwres_endhostent() are not thread safe; they return pointers to static data
and provide error codes through a global variable. Thread-safe versions
for name and address lookup are provided by lwres_gethostbyname_r(), and
lwres_gethostbyaddr_r() respectively.
The resolver daemon does not currently support any non-DNS name services
such as /etc/hosts or NIS, consequently the above functions don't, either.
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