c# - Why Regex IsMatch() hangs

Question

I have an exepression to validate an email address:

string REGEX_EMAIL = @"^w+([.!#$\%&'*+-/=?^`{|}~]*w+)*@w+([.-]w+)*.w+([.-]w+)*$";

If address is correct IsMatch() method quickly shows true result. But if address string is long and wrong this method hangs.

What can I do to raise speed of this method?

Thanks.

Answer 1

You are experiencing catastrophic backtracking.

The simplified regex:

Regex regexObj = new Regex(@"^w+([-.!#$%&'*+/=?^`{|}~]*w+)*@w+([.-]w+)*.w+([.-]w+)*$");

Has potential problems e.g. ([.-]w+)*.

If the . is missing for example and you have a long string of characters before it then all possible combinations must be taken into account for your regex to find out that it actually fails.