/* sig_src - tells you the source PID of a SIGHUP signal
 *
 * Steps:
 * 1. rename your target_program to target_program_real.
 * 2. The compile this program and name it target_program
 * 3. Go! sig_src (pretending to be target_program) will 
 *    launch your real target program, while standing by to
 *    intercept the SIGHUP
 *  
 *
 * Written by Marc Randolph (mrand)
 * This source code is provided for unrestricted use.
 * Users may copy or modify this source code without charge.
 * 
 * Rev history
 *   2.0  - 12 May 2009 - release to the wild
 *
 */

#define __USE_GNU
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <signal.h>



static void sigHandler ( int sig, siginfo_t *info, void *data ) {

  if ( info == NULL ) {

    fprintf ( stderr,
	      "signal: [%d]\n",
	      sig );

    return;

  } else {

    fprintf ( stderr,
	      "signo: [%d], errno: [%d], code: [%d], pid: [%d], uid: [%d]\n",
	      info->si_signo,  /* same as sig */
	      info->si_errno,
	      info->si_code,
	      info->si_pid,
	      info->si_uid );
  }
}

int main ( int argc, char *argv[] ) {

  char *suffix = "_real\0";
  char *args, *args_save;
  int argc_cnt, i;
  int char_cnt = 0;
  struct sigaction act;
  pid_t child_pid;

  memset ( &act, '\0', sizeof ( struct sigaction ) );

  /* Set up signal handler to catch SIGHUP */
  act.sa_sigaction = &sigHandler;
  act.sa_flags |= SA_SIGINFO;
  sigemptyset ( &act.sa_mask );
  sigaction ( SIGHUP, &act, NULL );


  /* count the number of characters in the argv list */
  for (argc_cnt = 0; argc_cnt < argc; argc_cnt++)
    char_cnt += strlen ( argv[argc_cnt] );

  /* calloc ( number of characters in argv + suffix + spaces + a null ) */
  args = calloc ( char_cnt + strlen ( suffix ) + argc_cnt + 1, 1);
  args_save = args;

  if (NULL == args) {
    fprintf(stderr, "No memory allocated.  Aborted.\n");
    exit ( 1 );
  }

  char_cnt = 0;

  /* Now combine argv list into a single null terminated string */
  for (argc_cnt = 0; argc_cnt < argc; argc_cnt++) {
    args = mempcpy ( args, argv[argc_cnt], strlen( argv[argc_cnt] ) );

    /* Special case: append first arg (our program name) with suffix */
    if (0 == argc_cnt)
      args = mempcpy (args, suffix, strlen(suffix) );

    *args++ = ' ';  /* add a space between every argument */
  }

  /* memory was null terminated to begin with */

  fprintf(stderr, "Executing (%s)\n", args_save);
#if 1
  child_pid = fork();
  if (0 == child_pid) {  /* child */
    system(args_save);
  } else {
    //    free(args);
    while (1)
      pause();
  }
#endif
  return ( 0 );

}