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

#define _POSIX_SOURCE 1 /* for fdopen */
#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 when you wrap a file around a pipe. 
   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];
   FILE *psFileChildToParent;
   enum {BUFFERSIZE=50};
   char pcDay[BUFFERSIZE], pcYear[BUFFERSIZE], pcMonth[BUFFERSIZE],
      pcNumDay[BUFFERSIZE], pcTime[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 the pipe */

   psFileChildToParent = fdopen(0, "r");

   fscanf(psFileChildToParent, "%s %s %s %s EST %s", pcDay, pcMonth,
          pcNumDay, pcTime, pcYear);
   printf("Day: %s\n", pcDay);
   printf("Month: %s\n", pcMonth);
   printf("NumDay: %s\n", pcNumDay);
   printf("Time: %s\n", pcTime);
   printf("Year: %s\n", pcYear);

   fclose(psFileChildToParent);

   return 0;
}

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

/* Sample execution:

$ gcc217 testpipewrapfile.c -o testpipewrapfile
$ ./testpipewrapfile
26247 parent
Day: Mon
Month: Dec
NumDay: 11
Time: 18:46:15
Year: 2017
*/