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

Verify the path exists and is readable: ls -l and test -r before invoking djpeg.

%s: can't open %s\n

Error message

%s: can't open %s\n

What it means

djpeg could not open the specified input file for binary reading. The program calls fopen(argv[file_index], READ_BINARY) and receives NULL, indicating the path is inaccessible. This is a hard failure: the process calls exit(EXIT_FAILURE) immediately after printing the message.

Source

Thrown at TMessagesProj/jni/mozjpeg/djpeg.c:587

  } else {
    if (file_index != argc - 1) {
      fprintf(stderr, "%s: must name one input and one output file\n",
              progname);
      usage();
    }
  }
#else
  /* Unix style: expect zero or one file name */
  if (file_index < argc - 1) {
    fprintf(stderr, "%s: only one input file\n", progname);
    usage();
  }
#endif /* TWO_FILE_COMMANDLINE */

  /* Open the input file. */
  if (file_index < argc) {
    if ((input_file = fopen(argv[file_index], READ_BINARY)) == NULL) {
      fprintf(stderr, "%s: can't open %s\n", progname, argv[file_index]);
      exit(EXIT_FAILURE);
    }
  } else {
    /* default input file is stdin */
    input_file = read_stdin();
  }

  /* Open the output file. */
  if (outfilename != NULL) {
    if ((output_file = fopen(outfilename, WRITE_BINARY)) == NULL) {
      fprintf(stderr, "%s: can't open %s\n", progname, outfilename);
      exit(EXIT_FAILURE);
    }
  } else {
    /* default output file is stdout */
    output_file = write_stdout();
  }

View on GitHub (pinned to 45ab8f4308)

Solutions

Verify the path exists and is readable: ls -l <path> and test -r <path> before invoking djpeg.
Use an absolute path or resolve relative to the known base directory instead of relying on the process cwd.
Confirm the file is a regular file, not a directory: [ -f <path> ].
Check filesystem mount and permissions (chmod/chown or Android sandbox grants).

Example fix

// before
./djpeg missing.jpg > out.ppm
// after - validate then run
test -f "$IN" || { echo "missing $IN"; exit 1; }
./djpeg "$IN" > out.ppm

Defensive patterns

Strategy: validation

Validate before calling

#include <sys/stat.h>
int can_read_input(const char *p) {
  struct stat st;
  if (stat(p, &st) != 0) return 0;          /* missing */
  if (!S_ISREG(st.st_mode)) return 0;        /* not a file */
  return access(p, R_OK) == 0;
}
/* call before exec djpeg with argv[file_index] */

Prevention

Resolve input paths to absolute form before invoking djpeg.
In shell wrappers, gate on test -f && test -r before running.
On Android, confirm the storage permission grant and content URI resolution.

When it happens

Trigger: Invoking djpeg with a path that does not exist, points to a directory instead of a file, lacks read permission, or is on an unmounted/unavailable filesystem. Triggered only when an explicit filename argument is given (file_index < argc); stdin is not involved here.

Common situations: Typo in the JPEG path, relative path evaluated from the wrong working directory, Android NDK build running with restrictive SELinux/AppArmor policies, file deleted between argument parsing and open, or a glob/variable expanding to a directory name.

Related errors

AI-assisted analysis of DrKLO/Telegram@45ab8f4308 (2026-08-14). Data as JSON: /api/errors/a3ad9a329ab38dfc. Report an issue: GitHub.