/*

This software is copyrighted by David N. Welton <davidw@dedasys.com>.
The following terms apply to all files associated with the software
unless explicitly disclaimed in individual files.

The authors hereby grant permission to use, copy, modify, distribute,
and license this software and its documentation for any purpose,
provided that existing copyright notices are retained in all copies
and that this notice is included verbatim in any distributions. No
written agreement, license, or royalty fee is required for any of the
authorized uses.  Modifications to this software may be copyrighted by
their authors and need not follow the licensing terms described here,
provided that the new terms are clearly indicated on the first page of
each file where they apply.

IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND
NON-INFRINGEMENT.  THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, AND
THE AUTHORS AND DISTRIBUTORS HAVE NO OBLIGATION TO PROVIDE
MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.

*/

/*
  Compile:
  gcc -shared -o TclDNS.so TclDNS.c

  From Tcl:

  tclsh8.3 [~/workshop/TclDNS]load ./TclDNS.so
  tclsh8.3 [~/workshop/TclDNS]dnslookup 198.186.203.20
  klecker.debian.org
*/

#include <tcl.h>
#include <netdb.h>

/*
 *-----------------------------------------------------------------------------
 *
 * TclDNS -- DNS lookups from Tcl.
 *
 * Accepts a dotted quad IP number, and returns either the same
 * string, if no lookup could be performed, or the resolved domain
 * name of the IP address.
 *
 *-----------------------------------------------------------------------------
 */
int Lookup(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[])
{
    char *address = NULL;
    Tcl_Obj *result = NULL;
    struct hostent *clienthost;
    struct hostent *hostname;
    if (objc != 2)
    {
	Tcl_WrongNumArgs(interp, 1, objv, "address");
	return TCL_ERROR;
    }
    address = Tcl_GetString(objv[1]);
    clienthost = gethostbyname(address);

    if (clienthost == NULL) {
	result = Tcl_NewStringObj(address, -1);
    } else {
	result = Tcl_NewStringObj(clienthost->h_name, -1);
	hostname = gethostbyaddr(clienthost->h_addr, 4, AF_INET);
	if (hostname != NULL) {
	    result = Tcl_NewStringObj(hostname->h_name, -1);
	}
    }

    Tcl_SetObjResult(interp, result);
    return TCL_OK;
}

int Tcldns_Init(Tcl_Interp *interp)
{
    Tcl_CreateObjCommand(interp, "dnslookup", Lookup,
			 (ClientData) NULL, (Tcl_CmdDeleteProc *) NULL);
    return TCL_OK;
}