copy_string error

[hailihu]

For a Landsat scene (LC81210622020202LGN00), force-l2ps exits with error "cannot copy, string too long.". This happens at line 699 of src/lower-level/gas-ll.c:
copy_string(source, NPOW_02, tokenptr)
because apparently tokenptr contains a too long string, printing it gives "MYD". This happens when reading a daily WVP_***.txt file where "MYD" is in the last column. Perhaps there is no end-of-string character for tokenptr? Anyways, replacing line 699 with:
strncpy(source, tokenptr, NPOW_02)
makes the preprocessing succeed.

[davidfrantz]

Hi Haili,

thanks for your suggestion. I really appreciate this.

But this is already fixed now with FORCE 3.5.2.

I would however suggest you not using your proposed fix as this is insecure (have a read here), and actually fails in this case.

The problem here is, that I forgot to replace the EOL character in the reading funtion, i.e. tokenptr = "MOD\n", should actually be tokenptr = "MOD\0"

This means that the copied string won't be null-terminated, which might cause other problems.

The copy_string function already did as you suggest, but adds a test whether the string is null-terminated after copying. As we were copying 4 (tokenptr = "MOD\n) instead of 3 characters (tokenptr = "MOD\0"), there was no space for the terminating NULL, and the function fails safely:

void copy_string(char *dst, size_t size, const char *src){

  strncpy(dst, src, size);
  if (dst[size-1] != '\0'){
    printf("cannot copy, string too long:\n%s\n", src);
    exit(1);
  }

  return;
}

The fix is to include this line here in src/lower-level/gas-ll.c in l. 682:

buffer[strcspn(buffer, "\r\n#")] = 0;

This even makes it safe to use a file with Windows EOL.

Cheers,

David

[hailihu]

Thanks David,
I tested 3.5.2 and it works now. It wasn't really a fix I proposed, just I workaround so I could identify the source of error and continue processing. Good you have a solid fix now, thanks!
Cheers, Haili