How to write a data annotation to check if email address found in string and fail on it

Question

I have the following code but it's not quite working... Any ideas where i'm going wrong? It seems to be failing when there is a carriage return in the string? (see fiddles at bottom)

[RegularExpression(@"^((?!([\w!#$%&'*+\-/=?\^_`{|}~]+(\.[\w!#$%&'*+\-/=?\^_`{|}~]+)*@((([\-\w]+\.)+[a-zA-Z]{2,4})|(([0-9]{1,3}\.){3}[0-9]{1,3})))).)*$", ErrorMessage = "Please do not include an email address in your description.")]

Context

People are writing descriptions and also placing email addresses in them, for example:

"Hi there i'm bob, here is my email: example@exampele.com. Hope you havea great day at my party."

I need to check that string and see that there is an email, and then not allow it to be submitted. (I'm using Entity framework and data annotations alongside the jquery validation in ASP .NET MVC 5... This is why i mentioned Data annotation usage.

Note:

I took the inversion technique from here:

Jquery validation on matching 'password' and 'admin' not working

And the email validation from here:

Best Regular Expression for Email Validation in C#

Attempts:

The following string:

http://pastebin.com/00BE7tUW

will show the error, whereas this will not:

http://pastebin.com/i69uxzRf

So something is a little wrong in the expression considering there is no email in it?

Fiddle:
Not working: https://regex101.com/r/zL7xD7/1
Working: https://regex101.com/r/hJ8fJ9/1
Working with email: https://regex101.com/r/dB3cU2/1

Answer 1

Have you tried something like this:

    bool invalid = false;

       public bool IsValidEmail(string strIn)
       {
           invalid = false;
           if (String.IsNullOrEmpty(strIn))
              return false;

           // Use IdnMapping class to convert Unicode domain names. 
           try {
              strIn = Regex.Replace(strIn, @"(@)(.+)$", this.DomainMapper,
                                    RegexOptions.None, TimeSpan.FromMilliseconds(200));
           }
           catch (RegexMatchTimeoutException) {
             return false;
           }

            if (invalid)
               return false;

           // Return true if strIn is in valid e-mail format. 
           try {
              return Regex.IsMatch(strIn,
                    @"^(?("")("".+?(?<!\\)""@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])@))" +
                    @"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9][\-a-z0-9]{0,22}[a-z0-9]))$",
                    RegexOptions.IgnoreCase, TimeSpan.FromMilliseconds(250));
           }
           catch (RegexMatchTimeoutException) {
              return false;
           }
       }

   private string DomainMapper(Match match)
   {
      // IdnMapping class with default property values.
      IdnMapping idn = new IdnMapping();

      string domainName = match.Groups[2].Value;
      try {
         domainName = idn.GetAscii(domainName);
      }
      catch (ArgumentException) {
         invalid = true;
      }
      return match.Groups[1].Value + domainName;
   }

The IsValidEmail method returns true if the string contains a valid email address and false if it does not, but takes no other action.

To verify that the email address is valid, the IsValidEmail method calls the Regex.Replace(String, String, MatchEvaluator) method with the (@)(.+)$ regular expression pattern to separate the domain name from the email address. The third parameter is a MatchEvaluator delegate that represents the method that processes and replaces the matched text.

Then you would check the email address by doing something like:

IsValidEmail(emailAddress)

Does this work for you?

Answer 2

The . needed to be replaced by [\S\s]

[RegularExpression(@"^((?!([\w!#$%&'*+\-/=?\^_`{|}~]+(\.[\w!#$%&'*+\-/=?\^_`{|}~]+)*@((([\-\w]+\.)+[a-zA-Z]{2,4})|(([0-9]{1,3}\.){3}[0-9]{1,3}))))[\S\s])*$", ErrorMessage = "Please do not include an email address in your field description.")]

source: Regular expression is not matching new lines