Best way to parse string of email addresses

Question

So i am working with some email header data, and for the to:, from:, cc:, and bcc: fields the email address(es) can be expressed in a number of different ways:

F         


        

Answer 1

I decided that I was going to draw a line in the sand at two restrictions:

1. The To and Cc headers have to be csv parseable strings.
2. Anything MailAddress couldn't parse, I'm just not going to worry about it.

I also decided I'm just interested in email addresses and not display name, since display name is so problematic and hard to define, whereas email address I can validate. So I used MailAddress to validate my parsing.

I treated the To and Cc headers like a csv string, and again, anything not parseable in that way I don't worry about it.

private string GetProperlyFormattedEmailString(string emailString)
    {
        var emailStringParts = CSVProcessor.GetFieldsFromString(emailString);

        string emailStringProcessed = "";

        foreach (var part in emailStringParts)
        {
            try
            {
                var address = new MailAddress(part);
                emailStringProcessed += address.Address + ",";
            }
            catch (Exception)
            {
                //wasn't an email address
                throw;
            }
        }

        return emailStringProcessed.TrimEnd((','));
    }

EDIT

Further research has showed me that my assumptions are good. Reading through the spec RFC 2822 pretty much shows that the To, Cc, and Bcc fields are csv-parseable fields. So yeah it's hard and there are a lot of gotchas, as with any csv parsing, but if you have a reliable way to parse csv fields (which TextFieldParser in the Microsoft.VisualBasic.FileIO namespace is, and is what I used for this), then you are golden.

Edit 2

Apparently they don't need to be valid CSV strings...the quotes really mess things up. So your csv parser has to be fault tolerant. I made it try to parse the string, if it failed, it strips all quotes and tries again:

public static string[] GetFieldsFromString(string csvString)
    {
        using (var stringAsReader = new StringReader(csvString))
        {
            using (var textFieldParser = new TextFieldParser(stringAsReader))
            {
                SetUpTextFieldParser(textFieldParser, FieldType.Delimited, new[] {","}, false, true);

                try
                {
                    return textFieldParser.ReadFields();
                }
                catch (MalformedLineException ex1)
                {
                    //assume it's not parseable due to double quotes, so we strip them all out and take what we have
                    var sanitizedString = csvString.Replace("\"", "");

                    using (var sanitizedStringAsReader = new StringReader(sanitizedString))
                    {
                        using (var textFieldParser2 = new TextFieldParser(sanitizedStringAsReader))
                        {
                            SetUpTextFieldParser(textFieldParser2, FieldType.Delimited, new[] {","}, false, true);

                            try
                            {
                                return textFieldParser2.ReadFields().Select(part => part.Trim()).ToArray();
                            }
                            catch (MalformedLineException ex2)
                            {
                                return new string[] {csvString};
                            }
                        }
                    }
                }
            }
        }
    }

The one thing it won't handle is quoted accounts in an email i.e. "Monkey Header"@stupidemailaddresses.com.

And here's the test:

[Subject(typeof(CSVProcessor))]
public class when_processing_an_email_recipient_header
{
    static string recipientHeaderToParse1 = @"""Lastname, Firstname"" " + "," +
                                           @", testto1@domain.com, testto2@domain.com" + "," +
                                           @", test3@domain.com" + "," +
                                           @"""""Yes, this is valid""""@[emails are hard to parse!]" + "," +
                                           @"First, Last , name@domain.com, First Last "
                                           ;

    static string[] results1;
    static string[] expectedResults1;

    Establish context = () =>
    {
        expectedResults1 = new string[]
        {
            @"Lastname",
            @"Firstname ",
            @"",
            @"testto1@domain.com",
            @"testto2@domain.com",
            @"",
            @"test3@domain.com",
            @"Yes",
            @"this is valid@[emails are hard to parse!]",
            @"First",
            @"Last ",
            @"name@domain.com",
            @"First Last "
        };
    };

    Because of = () =>
    {
        results1 = CSVProcessor.GetFieldsFromString(recipientHeaderToParse1);
    };

    It should_parse_the_email_parts_properly = () => results1.ShouldBeLike(expectedResults1);
}