[ragel-users] Intermediate match wrongly assumed as valid

[Iñaki Baz Castillo]

Hi,

After many years using my Ragel based IPv6 parser, I've found a bug. I
think I've also understood the problem and simplified the code as much
as possible.

Let's assume this simple grammar:

--------------------
foo = "12345" | "123";
-------------------

The parser.rl has a function that receives a char* data pointer and a
size_t len. It includes the Ragel %% lines as usual. At the end of the
function it checks:

--------------------
// Ensure that the parsing has consumed all the given length.
if (len == p - data)
  return true;
else
  return false;
--------------------

The problem is that, when the input is "1234", the parser returns true.

I think I understand the problem:

- The parser first matches "123" which is valid.
- It continues and matches "1234".
- At this time it has consumed 4 chars.
- It exits now because there is no more chars in the input.
- However it did match "123" so the Ragel action was executed.

May I know how to avoid this problem and make the parser function
return false in this case?

Thanks a lot.



-- 
Iñaki Baz Castillo
<ibc at aliax.net>