What is wrong with this Regex "^(.|\s){1,280}$"

Should be validating 1-280 input characters, but it hangs when more than 280 characters are input.

Clarification I am using the above regex to validate the length of input string to be 280 characters max开发者_JS百科imum. I am using asp:RegularExpressionValidator to do that.

There's nothing “wrong” with it per se, but it's horrendous because with most RE engines (you don't say which one you're using) when it doesn't match with the first thing it tries because it causes the engine to backtrack and try loads of different possibilities (none of which can ever cause a match). So it's not a hang, but rather just a machine that's trying to execute around 2²⁸⁰ operations to see if there's a match possible. Excuse me if I don't wait around for that!

Of course, it's theoretically possible for the RE compiler to merge the (.|\s) part of the RE into something it doesn't need to backtrack to deal with. Some RE engines do this (typically the more automata-theoretic ones) but many don't (the stack-based ones).

It is trying every possible combination of . and \s for each character trying to find a version of the pattern that matches the string.

. already matches any character, so (.|\s) is redundant. Further, if you just want to check what the length of the string is, then just do that - why are you pulling out regexes?

If you really want to use a regular expression, you could use .{1, 280}$ combined with the SingleLine option, so that the . metacharacter will match everything, including new lines (see here, Regular Expression API section).