[Dovecot] coding techniques

[David Lee]

Whilst debugging a problem in dovecot LDA over the last few days, I came
across two different issues in coding techniques.

(Note: Please don't take this negatively; my intent is both positive and
constructive!)

The front page of the website www.dovecot.org says:
  "it uses several coding techniques to avoid most of the common pitfalls"

So I hope it is OK to follow the spirit of that with some suggestions.


The two issues I encountered both seem to be fairly easy holes to fall
into, and yet equally easy to avoid in the first place by using
established C practices.

Firstly, many 'if' statements having a single statement (whether in then
or else part) are currently written in a short-cut fashion:

   if (condition)
      statement 1;
   else
      statement 2;

This, though technically legal, is potentially lethal when inserting (say)
debugging statements.  Without diligence it is all to easy to produce:

   if (condition)
      debug 1a;
      statement 1;
      debug 1b;
   else
      debug 2a;
      statement 2;
      debug 2b;

A simple edit that looks, layout-wise, as if it would do the right thing
(and do in Python!); but actually radically changes the execution flow.
(This is left as an exercise to the reader... to demonstrate the point.)

Could I suggest that the relevant brackets be always used as a matter of
course?  Something like:

   if (condition) {
      statement 1;
   } else {
      statement 2;
   }

Then the insertion of debug statements doesn't inflict surprise.

(No, I didn't fall into this hole.  But it is a trap waiting to happen.)


Secondly, code duplication.  To give one example: 'get_var_expand_table()'
appears in both 'deliver/deliver.c' and 'master/mail-process.c'.  (There
is also a similar looking function in 'auth/auth-request.c'.)  Perhaps
consideration should be given to merging such instances.  For instance, my
woes with "%i"-expansion being treated differently in mail-reading and
mail-delivery would likely never have arisen if common code had been used.

I hope that helps (constructively!).

Best wishes.



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