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utils-std

Collection of commonly available Unix tools git clone https://anongit.hacktivis.me/git/utils-std.git/

mesg.c (1837B)

    

  1. // utils-std: Collection of commonly available Unix tools
  2. // SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
  3. // SPDX-License-Identifier: MPL-2.0
  5. #define _POSIX_C_SOURCE 200809L
  6. #include <errno.h>
  7. #include <stdio.h>
  8. #include <string.h>
  9. #include <sys/stat.h> // stat, chmod
  10. #include <unistd.h>   // ttyname
  12. int
  13. main(int argc, char *argv[])
  14. {
  15. 	argc -= 1;
  16. 	argv += 1;
  18. 	if(argc > 1)
  19. 	{
  20. 		fprintf(stderr, "mesg: error: Expected either 0 or 1 argument, got %d\n", argc);
  21. 		return 2;
  22. 	}
  24. 	if(argc == 1)
  25. 	{
  26. 		if(argv[0][0] == '\0')
  27. 		{
  28. 			fputs("mesg: error: argument is empty, expected 'y' or 'n'\n", stderr);
  29. 			return 2;
  30. 		}
  31. 		if(argv[0][1] != '\0')
  32. 		{
  33. 			fputs("mesg: error: argument is too long, expected 'y' or 'n'\n", stderr);
  34. 			return 2;
  35. 		}
  36. 		if(argv[0][0] != 'y' && argv[0][0] != 'n')
  37. 		{
  38. 			fprintf(stderr, "mesg: error: unknown argument '%s', expected 'y' or 'n'\n", argv[0]);
  39. 			return 2;
  40. 		}
  41. 	}
  43. 	char *tty = ttyname(STDIN_FILENO);
  44. 	if(!tty) ttyname(STDOUT_FILENO);
  45. 	if(!tty) ttyname(STDERR_FILENO);
  46. 	if(!tty)
  47. 	{
  48. 		fputs("mesg: error: Could not determine TTY from stdin/stdout/stderr\n", stderr);
  49. 		return 2;
  50. 	}
  52. 	struct stat tty_st;
  53. 	if(stat(tty, &tty_st) < 0)
  54. 	{
  55. 		fprintf(
  56. 		    stderr, "mesg: error: Failed getting file status from '%s': %s\n", tty, strerror(errno));
  57. 		return 2;
  58. 	}
  60. 	if(argc == 0)
  61. 	{
  62. 		if((tty_st.st_mode & 0022) == 0022)
  63. 		{
  64. 			fputs("messages allowed\n", stdout);
  65. 			return 0;
  66. 		}
  68. 		fputs("messages denied\n", stdout);
  69. 		return 1;
  70. 	}
  72. 	mode_t new_mode = tty_st.st_mode;
  73. 	if(argv[0][0] == 'y')
  74. 		new_mode |= 0022;
  75. 	else
  76. 		new_mode &= ~0022;
  78. 	if(chmod(tty, new_mode) < 0)
  79. 	{
  80. 		fprintf(stderr,
  81. 		        "mesg: error: Failed setting new mode (0%03o) on terminal '%s': %s\n",
  82. 		        new_mode,
  83. 		        tty,
  84. 		        strerror(errno));
  85. 		return 2;
  86. 	}
  88. 	return 0;
  89. }