What causes "Comment text may not exceed %u bytes " in DrKLO/Telegram?

Keep comment text under 65000 bytes; for larger payloads use -cfile with a file instead.

Comment text may not exceed %u bytes

Error message

Comment text may not exceed %u bytes

What it means

When -comment is given a value whose first character is a double-quote, wrjpgcom assumes an MS-DOS-style quoted string and allocates a MAX_COM_LENGTH (65000) byte buffer to reassemble it. This error fires when even the very first token is too long: strlen(argv[argn]) + 2 >= MAX_COM_LENGTH. The +2 accounts for the appended space and terminator used while concatenating further tokens. The process exits EXIT_FAILURE.

Source

Thrown at TMessagesProj/jni/mozjpeg/wrjpgcom.c:451

      keep_COM = 0;
    } else if (keymatch(arg, "cfile", 2)) {
      if (++argn >= argc) usage();
      if ((comment_file = fopen(argv[argn], "r")) == NULL) {
        fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
        exit(EXIT_FAILURE);
      }
    } else if (keymatch(arg, "comment", 1)) {
      if (++argn >= argc) usage();
      comment_arg = argv[argn];
      /* If the comment text starts with '"', then we are probably running
       * under MS-DOG and must parse out the quoted string ourselves.  Sigh.
       */
      if (comment_arg[0] == '"') {
        comment_arg = (char *)malloc((size_t)MAX_COM_LENGTH);
        if (comment_arg == NULL)
          ERREXIT("Insufficient memory");
        if (strlen(argv[argn]) + 2 >= (size_t)MAX_COM_LENGTH) {
          fprintf(stderr, "Comment text may not exceed %u bytes\n",
                  (unsigned int)MAX_COM_LENGTH);
          exit(EXIT_FAILURE);
        }
        strcpy(comment_arg, argv[argn] + 1);
        for (;;) {
          comment_length = (unsigned int)strlen(comment_arg);
          if (comment_length > 0 && comment_arg[comment_length - 1] == '"') {
            comment_arg[comment_length - 1] = '\0'; /* zap terminating quote */
            break;
          }
          if (++argn >= argc)
            ERREXIT("Missing ending quote mark");
          if (strlen(comment_arg) + strlen(argv[argn]) + 2 >=
              (size_t)MAX_COM_LENGTH) {
            fprintf(stderr, "Comment text may not exceed %u bytes\n",
                    (unsigned int)MAX_COM_LENGTH);
            exit(EXIT_FAILURE);
          }

View on GitHub (pinned to 45ab8f4308)

Solutions

Keep comment text under 65000 bytes; for larger payloads use -cfile with a file instead.
If the text legitimately exceeds the limit, store it in a file and pass -cfile <file>.
Trim or chunk the comment source before constructing the argv.

Example fix

// before
wrjpgcom -comment "$(cat huge.txt)" photo.jpg
// after
wrjpgcom -cfile huge.txt photo.jpg

Defensive patterns

Strategy: validation

Validate before calling

#define MAX_COM_LENGTH 65000L
/* before building argv, check the quoted comment's first token length */
if (comment[0] == '"' && strlen(comment) + 2 >= (size_t)MAX_COM_LENGTH) {
    /* route long comments through -cfile instead */
}

Prevention

Treat any comment >= ~64KB as a file payload, not an argv string.
Bound user-supplied comment length at the input boundary.
Prefer -cfile for programmatically generated comments.

When it happens

Trigger: Running `wrjpgcom -comment "<very long string>"` where the single quoted token (minus trailing quote considerations) already reaches/exceeds 64998 bytes, so no further tokens could ever fit.

Common situations: Piping a huge blob into a shell-quoted -comment argument, accidentally passing a file's full contents as an argument, or a script concatenating unbounded user input into the comment.

Related errors

AI-assisted analysis of DrKLO/Telegram@45ab8f4308 (2026-08-14). Data as JSON: /api/errors/6be5f6232a02e7f7. Report an issue: GitHub.