What causes "%s: can't open %s " in DrKLO/Telegram?

Verify the file exists and is readable: ls -la or test -r .

%s: can't open %s

Error message

%s: can't open %s

What it means

rdjpgcom attempts to fopen the user-specified input file in binary read mode (READ_BINARY). If fopen returns NULL, the file could not be opened -- typically because it does not exist, permissions are insufficient, or the path is a directory. The program prints this error with the file path and exits with EXIT_FAILURE.

Source

Thrown at TMessagesProj/jni/mozjpeg/rdjpgcom.c:487

      break;                    /* not switch, must be file name */
    arg++;                      /* advance over '-' */
    if (keymatch(arg, "verbose", 1)) {
      verbose++;
    } else if (keymatch(arg, "raw", 1)) {
      raw = 1;
    } else
      usage();
  }

  /* Open the input file. */
  /* Unix style: expect zero or one file name */
  if (argn < argc - 1) {
    fprintf(stderr, "%s: only one input file\n", progname);
    usage();
  }
  if (argn < argc) {
    if ((infile = fopen(argv[argn], READ_BINARY)) == NULL) {
      fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
      exit(EXIT_FAILURE);
    }
  } else {
    /* default input file is stdin */
#ifdef USE_SETMODE              /* need to hack file mode? */
    setmode(fileno(stdin), O_BINARY);
#endif
#ifdef USE_FDOPEN               /* need to re-open in binary mode? */
    if ((infile = fdopen(fileno(stdin), READ_BINARY)) == NULL) {
      fprintf(stderr, "%s: can't open stdin\n", progname);
      exit(EXIT_FAILURE);
    }
#else
    infile = stdin;
#endif
  }

  /* Scan the JPEG headers. */

View on GitHub (pinned to 45ab8f4308)

Solutions

Verify the file exists and is readable: ls -la <path> or test -r <path>.
Check the full path for typos and correct relative/absolute path usage.
Fix file permissions: chmod +r <path> or ensure the running user has access.
If the path is a directory, remove it or pass the actual file path.

Example fix

# before
rdjpgcom /wrong/path/image.jpg
# after
rdjpgcom ./images/image.jpg

Defensive patterns

Strategy: validation

Validate before calling

# Check file exists and is readable before invoking rdjpgcom
if [ ! -r "$input" ]; then
  echo "Error: cannot read $input" >&2
  exit 1
fi
rdjpgcom "$input"

Prevention

Use test -r <path> to verify readability before passing to CLI tools.
Use absolute paths to avoid working-directory ambiguity.
Check file permissions with ls -la when debugging access errors.

When it happens

Trigger: Passing a file path that does not exist; a path with insufficient read permissions; a path that is a directory rather than a file; a path with incorrect escaping or quoting in the shell.

Common situations: Typo in the filename; relative path used from the wrong working directory; file on an unmounted or disconnected volume; file owned by another user with no read access; Android environment where the path is in a protected directory.

Related errors

AI-assisted analysis of DrKLO/Telegram@45ab8f4308 (2026-08-14). Data as JSON: /api/errors/57bc379aab0e35f2. Report an issue: GitHub.