/* mopen.c - test of multiple open() calls for same file 
   args:  filename, followed by 0 or more switches 
          -r  for O_RDONLY,  -w  for O_WRONLY,  -rw  for O_RDWR
   this program attempts to open arg1 once for each switch supplied, 
   but always at least twice.  Default flag is O_RDONLY */

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

#define MAXSTRING 100 /* maximum size for strings */

/* try_open
     2 args:  file name (string), value for flags 
     return:  return value from open
     state change:  return from open() is printed on standard output */
int try_open(char *filename, int FLAGS)
{
  char *flagstr;  /* representation of FLAGS as a string */
  int ret_val;  /* return value from open() */

  switch (FLAGS) {
  case O_RDONLY:  flagstr = "O_RDONLY"; break;
  case O_WRONLY:  flagstr = "O_WRONLY"; break;
  case O_RDWR:  flagstr = "O_RDWR"; break;
  default:  printf("try_open:  unrecognized flag %d\n", FLAGS); exit(1); break;
  }
  printf("open(%s, %s) returned ", filename, flagstr);
  if ((ret_val = open(filename, FLAGS)) < 0) {
    printf("error %d\n", ret_val);
    perror("try_open: ");
 }
  else 
    printf("file descriptor %d\n", ret_val);
  return ret_val;
}

int main(int argc, char *argv[])
{
  char *filename;  /* name of file to be multiply opened */
  char *progname = argv[0];  /* name of this program */
  char *getlinebuff = NULL;
  size_t getlinelen = 0;

  if (argc == 1)
    { printf("usage:  %s filename [ -r|-w|-rw ] ...\n", progname); 
      exit(1); }
  /* at least one command-line arg was provided*/

  filename = argv[1];
  argv += 2;  argc -= 2;
  /* there are argc switches, beginning at argv[0] */

  switch (argc) {
  case 0:  
    try_open(filename, O_RDONLY); 
    try_open(filename, O_RDONLY);
    break;

  case 1:
    try_open(filename, O_RDONLY);

  default:
    while (*argv)
      {
	if (!strcmp("-r", argv[0]))
	  try_open(filename, O_RDONLY);
	else if (!strcmp("-w", argv[0]))
	  try_open(filename, O_WRONLY);
	else if (!strcmp("-rw", argv[0]))
	  try_open(filename, O_RDWR);
	else {
	  fprintf(stderr, "Unrecognized switch \"%s\" -- aborting\n", 
		  argv[0]);
	  exit(1);
	}
	/* switch was valid */
	argv++;
      }
    break;
  }
  printf("Enter commands using the following syntax:  (count < %d)\n",
	 MAXSTRING);
  printf("    read <fd> <count>\n    write <fd> <string>\n    quit\n");
  while (1) {
    char cmd[MAXSTRING];  /* command entered by user */
    int fd;  /* file descriptor entered by user */
    char buff[MAXSTRING];  /* a string buffer for I/O */
    int ret_val;  /* return value from a system call */

    printf("read write quit:  ");
    if ((ret_val = scanf("%s", cmd)) == EOF)
      exit(0);
    /* assert:  one word was read into cmd */

    /***** read command *****/
    if (!strcmp(cmd, "read")) {
      int count;  /* number of chars to read */

      scanf("%d %d", &fd, &count);
      if (count >= MAXSTRING) {
	printf("%d is too many characters -- try reading fewer than %d\n",
	       count, MAXSTRING);
	continue;
      }
      /* count is small enough */
      if ((ret_val = read(fd, buff, count)) < 0)
	printf("Error code %d returned\n", ret_val);
      else {
	buff[ret_val] = '\0';
	printf("%d bytes were read:  \"%s\"\n", ret_val, buff);
      }


    /***** write command *****/
    } else if (!strcmp(cmd, "write")) {
      scanf("%d ", &fd);
      int nchars = getline(&getlinebuff, &getlinelen, stdin);
      if ((ret_val = write(fd, getlinebuff, nchars-1)) < 0)
	printf("Error code %d returned\n", ret_val);
      else 
	printf("%d bytes written\n", ret_val);


    /***** quit command *****/
    } else if (!strcmp(cmd, "quit")) 
      break;


    else 
      printf("Unrecognized command %s\n", cmd);
  }

  free(getlinebuff);
  exit(0);
}