The fix wasn't easy, or C precedence bites

For the past decade now, I've done a Christmas release for mod_blog (only missing the years 2019 and 2023), just beacuse. I was poking around the codebase looking for changes I could make for Christmas this year, and well, I got a bit impatient and have just now released a version in time for Halloween. And it's scary—I'm removing features!

I've removed features in the past, like no longer supporting “ping servers” when it became clear it wasn't worth it, or automatically updating Linked­Tik­Face­My­Insta­Pin­Me­Gram­We­Tok­In­Book­Space­Trest when Insta­Pin­Tik­My­Linked­Face­Me­Trest­Book­Gram­We­In­Space­Tok changed how it works often enough to make it annoying for me to continue. But this time … this time it's different. This is removing functionality that has existed in the code base since the beginning!

To make it easier to write entries, I had code within mod_blog to process the input—mostly what existed was to convert sequences like ``quoted'' to “quoted” and “...” to “…”, but with an option to add <P> tags around logical paragraphs. But given that I now use my own markup language, I rarely used the web interface (like, I can count on my fingers the number of times I've used it and still have a few left over should give an indication of how little I use it) and the code just sat there, unused. So unused that in fixing one bug I introduced another bug in the code I fixed!

To recap, here's the original code:

char UrlDecodeChar(char **psrc)
{
  char *src;
  char  c;
  
  assert(psrc  != NULL);
  assert(*psrc != NULL);
  
  src = *psrc;
  c   = *src++;
  if (c == '+')
    c = ' ';
  else if (c == '%')
  {
    assert(isxdigit(*src));
    assert(isxdigit(*(src+1)));
    c    = ctohex(*src) * 16 + ctohex(*(src+1));
    src += 2;
  }
  *psrc = src;
  return(c);
}

and the “fixed” version:

char UrlDecodeChar(char **psrc)
{
  char *src;
  char  c;
  
  assert(psrc  != NULL);
  assert(*psrc != NULL);
  
  src = *psrc;
  c   = *src++;
  if (c == '+')
    c = ' ';
  else if (c == '%')
  {
    if (!isxdigit(*src))   return '\0';
    if (!isxdigit(*src+1)) return '\0';
    c    = ctohex(*src) * 16 + ctohex(*(src+1));
    src += 2;
  }
  *psrc = src;
  return(c);
}

I don't fault you if you can't spot the bug. I only found it when testing the web interface to ensure it wasn't completely broken with the conversion code removed (instead it's now only mostly broken but that's an interesting case in and of itself and requires its own post). The bug is in this line of code:

if (!isxdigit(*src+1)) return '\0';

The issue is due to C's precedence rules and dereferencing rules. The code above is parsed as src[0] + 1 instead of the src[1] that I was intending. When I modified the function, changing the calls to assert() into actual code to return an error (I typed in the new code as that's faster than modifying the existing code) I … kind of missed that.

Oh, who am I kidding? I totally missed that. But because I don't use the web interface this bug went unnoticed. Sigh.

For the record, I changed the code to read:

if (!isxdigit(src[0])) return '\0';
if (!isxdigit(src[1])) return '\0';
c    = ctohex(src[0]) * 16 + ctohex(src[1]);

Another long time feature I've removed is email notification. I added it early on where you could submit your email address to get notified of posts, but spammers and a lack of outside interest pretty much put the kibosh on that. As I still have three users of the email notification (one is me, one is Bunny, and one is one other person whom I'm not sure still reads the emails but they haven't bounced yet) I don't want to drop support completely, so now the email notifications are sent via the hook mechanism I added a few years ago.

In total, I removed over 3,000 lines of code from mod_blog. Granted, over 2,000 of them were in one function that was removed, but still, it's 3,000 lines of code I don't have to worry about any more.

Still, it's a bit scary to remove features that have been there for so long, and thus, a Halloween release.

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