/*--------------------------------------------------------------------*/
/* testdupforkexecpipe.c                                              */
/* Author: Iasonas Petras                                             */
/*--------------------------------------------------------------------*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>

/*--------------------------------------------------------------------*/

/* Demonstrate the fork(), creat(), close(), pipe() and dup() 
   system-level functions. As usual, argc is the command-line 
   argument count, and
   argv contains the command-line arguments. Return 0. */

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

   pid_t iPid;
   int iRet;
   int ChildToParent[2];
   enum {BUFFERSIZE=50};
   char cbuffer[BUFFERSIZE];


   printf("%d parent\n", (int)getpid());

   if(pipe(ChildToParent)) {perror(argv[0]); exit(EXIT_FAILURE); }

   iRet = fflush(NULL);
   if (iRet == EOF) {perror(argv[0]); exit(EXIT_FAILURE); }

   iPid = fork();
   if (iPid == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

   if (iPid == 0)
   {
      char *apcArgv[2];
      int iRet;

      /* Redirect stdout to the "out part" of the pipe */

      iRet = close(1);
      if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

      iRet = dup(ChildToParent[1]);
      if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

      /* Close the pipe */

      iRet = close(ChildToParent[0]);
      if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

      iRet = close(ChildToParent[1]);
      if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

      apcArgv[0] = "date";
      apcArgv[1] = NULL;
      execvp("date", apcArgv);
      perror(argv[0]);
      exit(EXIT_FAILURE);
   }

   iPid = wait(NULL);
   if (iPid == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

   /* This code is executed by only the parent process. */

   iRet = close(ChildToParent[1]);
   if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

   iRet = close(0);
   if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

   iRet = dup(ChildToParent[0]);
   if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }      

   iRet = close(ChildToParent[0]);
   if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }


   /* Read in a string from stdin (alies the read part
      of the pipe) */
   (void) read(0, cbuffer, sizeof(cbuffer));
   printf("Current date: %s (In Parent process %d)\n", cbuffer, getpid());
   
   return 0;
}

/*--------------------------------------------------------------------*/

/* Sample execution:

$ gcc217 testdupforkexecpipe.c -o testdupforkexecpipe
$ ./testdupforkexecpipe
2018 parent
Current date: Thu Dec 14 12:55:14 EST 2017
 (In Parent process 2018)


*/