Re: Error handling (was Re: [ANN] Lua 5.3.0 (final) now available)

[Sean Conner <sean@...>]

It was thus said that the Great Andrew Starks once stated:
> 
> If you always error, you can
> pretend that errors never happen, until you can't. In a garbage
> collected language, the places where you need to clean the state up
> are pretty limited, so this may be more true of Lua than of C, or
> whathaveyou.

  But you can still leak resources if you don't clear your references.  I
just found such a bug at work at one place, and now I'm afraid of all the
paths I neglected to clean up references leading up to that point.  

  And the path is checking a SIP message for validity, so it's a lot of 

	if not this_header then
	  reply "you bozo!"
	end

	if this_header ~= "that" then
	  reply "you bozo!"
	end

  And I can't just toss an error here because there are two (or three, if
you squint) distinct phases to the processing:

	We've received the initial message, check for validity and send back
	ACK or NAK.
	
	Send a new message to something else (it may be the oritinal sender;
	it may not be), and wait for an ACK or NACK.

which is running as a coroutine, which has its own peculiarities.

  Handling errors in the first half is different from the second half (the
third phase is just skipping the second phase if we receive a particual
message).  

> `return nil, error_msg` forces you to write more code every time you
> call that function.

  But that's pretty much what I"m doing now.

  -spc (Off to check all the code paths now ... sigh)