gethost.c revision ec5347e2c775f027573ce5648b910361aa926c01
/*
* Copyright (C) 2004, 2005 Internet Systems Consortium, Inc. ("ISC")
* Copyright (C) 2000, 2001 Internet Software Consortium.
*
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
* OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
/* $Id: gethost.c,v 1.33 2007/06/18 23:47:51 tbox Exp $ */
/*! \file */
/**
* 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>.
*
* \code
* 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
* \endcode
*
* The members of this structure are:
*
* \li h_name:
* The official (canonical) name of the host.
*
* \li h_aliases:
* A NULL-terminated array of alternate names (nicknames) for the
* host.
*
* \li h_addrtype:
* The type of address being returned -- PF_INET or PF_INET6.
*
* \li h_length:
* The length of the address in bytes.
*
* \li 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
* 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 hostent for 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.
*
* \section gethost_return 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
*
* \li #HOST_NOT_FOUND:
* The host or address was not found.
*
* \li #TRY_AGAIN:
* A recoverable error occurred, e.g., a timeout. Retrying the
* lookup may succeed.
*
* \li #NO_RECOVERY:
* A non-recoverable error occurred.
*
* \li #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() 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.
*
* \section gethost_see See Also
*
* gethostent(), \link getipnode.c getipnode\endlink, lwres_hstrerror()
*
* \section gethost_bugs 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
* don't, either.
*/
#include <config.h>
#include <errno.h>
#include <string.h>
#include "assert_p.h"
#define LWRES_ALIGNBYTES (sizeof(char *) - 1)
#define LWRES_ALIGN(p) \
(((unsigned long)(p) + LWRES_ALIGNBYTES) &~ LWRES_ALIGNBYTES)
/*% Always looks for an IPv4 address. */
struct hostent *
lwres_gethostbyname(const char *name) {
return (he);
}
/*% Looks for either an IPv4 or IPv6 address. */
struct hostent *
return (he);
}
/*% Reverse lookup of addresses. */
struct hostent *
return (he);
}
/*% Stub function. Always returns failure. */
struct hostent *
lwres_gethostent(void) {
return (NULL);
}
/*% Stub function. Always returns failure. */
void
lwres_sethostent(int stayopen) {
/*
* Empty.
*/
}
/*% Stub function. Always returns failure. */
void
lwres_endhostent(void) {
/*
* Empty.
*/
}
/*% Thread-safe function for forward lookups. */
struct hostent *
{
int res;
return (NULL);
if (res != 0) {
return (NULL);
}
return (resbuf);
}
/*% Thread-safe reverse lookup. */
struct hostent *
int *error)
{
int res;
return (NULL);
if (res != 0) {
return (NULL);
}
return (resbuf);
}
/*% Stub function. Always returns failure. */
struct hostent *
*error = 0;
return (NULL);
}
/*% Stub function. Always returns failure. */
void
lwres_sethostent_r(int stayopen) {
/*
* Empty.
*/
}
/*% Stub function. Always returns failure. */
void
lwres_endhostent_r(void) {
/*
* Empty.
*/
}
static int
char *cp;
char **ptr;
int i, n;
/*
* Find out the amount of space required to store the answer.
*/
}
}
return (-1);
}
/*
* Copy address size and type.
*/
/*
* Copy address list.
*/
cp += n;
}
ptr++;
/*
* Copy official name.
*/
cp += n;
/*
* Copy aliases.
*/
cp += n;
}
return (0);
}