Regex length validation: Ignore leading and trailing whitespaces

Question

I'm trying to limit our users between 5 and 1024 characters per post.

We are currently using asp.net RegularExpressionValidator for this.

This is kinda working if I set the expression to the following:

body.ValidationExpression = string.Format("^[\\s\\S]{{{0},{1}}}$",
        MinimumBodyLength,
        MaximumBodyLength);

However, this does not take NewLines and leading/tailing/multiple spaces into account. So users can type stuff like: Ok (three spaces) . (dot), and it will still be validated because three spaces count as characters. The same goes for newlines. We can also type a single . (dot) followed by 5 spaces/newlines.

I have tried multiple regex variations I've found around the web, but none seem to fit my needs exactly. I want them to type minimum 5 characters, and maximum 3000 characters, but I don't really care how many newLines and spaces they use.

To clearify, I want people to be able to type:

Hi,
My name is ben

I do not want them to be able to type:

Hi                  .

or

A              B

(lots of newlines or spaces)

It is possible that regex might not be the way to go? If so, how can I search and replace on the string before the regex evaluates (while still catch it in the validator with the old expression)?

Answer 1

Use the regex below:

body.ValidationExpression = string.Format("^((\S)|((\s+|\n+|(\r\n)+)+\S)|(\S(\s+|\n+|(\r\n)+))+){{{0},{1}}}$",
    MinimumBodyLength,
    MaximumBodyLength);

It treats as single entity either a single character or single character after (or before) any number of whitespace characters.