[Cryptography] GOTO Considered Harmful

[Derek Atkins]

On Fri, February 28, 2014 1:07 pm, Patrick Chkoreff wrote:
> I refactored Apple's code:
>
> http://fexl.com/goto-considered-harmful
>
> You're welcome.

Sorry, Patrick, but your code doesn't work, either.  Indeed, your code can
be made to return success by having 'failed' turned on at the beginning. 
Then you'll hit the line:

    failed ||= ((err = SSLHashSHA1.final(&hashCtx, &hashOut)) != 0);

Which will most likely set err to OK (because, honestly, SHA1 final never
fails.  Then it will fall though to:

    return err;

Eh viola, no error code returned.

A better approach would be a set of:

do {
  ...
} while (0);

sections.  E.g.

  do {
     if ((err = ReadyHash(&SSLHashMD5, &hashCtx)) != 0) break;
     ...
  while (0);

Or:

  if (!err) err = ReadyHash(&SSLHashSHA1, &hashCtx);
  if (!err) ....


This way you will always make sure you return an error, and you are
guaranteed to return the first error you hit.

Or drop the code and use C++ exceptions ;)

-derek

-- 
       Derek Atkins                 617-623-3745
       derek at ihtfp.com             www.ihtfp.com
       Computer and Internet Security Consultant