Safely insert line breaks into HTML

Question

I have an application allows a user to copy paste html into a form. This html gets sent as an email, and the email server will not allow more than 1000 characters per line. So, I'd like to insert line breaks (\r\n) into the html after the user has hit submit. How can I do this without changing the content?

My idea is this:

html.replace('<', '\r\n<');

But is that guaranteed to not change the result? Is '<' not allowed in attributes?

Edit: I'm actually thinking this will not work because the html could have a script block with something like if(x < 3). I guess what I need is an html pretty printer that works in either js or C#.

Answer 1

I am not sure how you are delivering your email... if it is handed off to a php script that then send it to a mail server or uses the mail() method, then this link might help.

http://php.net/manual/en/function.wordwrap.php

If not, can you clarify your question a bit?

Another simply thought, is that you could use: html.replace('','\r\n'); or: html.replace('',''+String.fromCharCode(13));//inserts a carriage return

However, since the will ideally be parsed in the browser, inserting "\r\n" may not be effective and may actually just display as "\r\n"....

Hope any of this is helpful.

Answer 2

Email MIME standard uses transfer encoding techniques to solve this problem. Ideally you would be using a mail library that takes care of this for you, so you can insert lines of any length.

Using the System.Net.Mail.MailMessage class in C#, you should be able to construct a normal message and it will transfer-encode it for you. If that doesn't work, you can also construct a multi-part message with a single System.Net.Mail.AlternativeView and set the transfer-encoding explicitly.

Here is a sample I am currently using (note it has a character encoding bug, so your body text must be a unicode string):

private void Send(string body, bool isHtml, string subject, string recipientAddress, string recipientName, string fromAddress)
{
    using (var message = new MailMessage(new MailAddress(fromAddress),
                                    new MailAddress(recipientAddress, recipientName)))
    {
        message.Subject = subject;
        var alternateView = AlternateView.CreateAlternateViewFromString(body, message.BodyEncoding,
                                                                        isHtml ? "text/html" : "text/plain");
        alternateView.TransferEncoding = TransferEncoding.QuotedPrintable;
        message.AlternateViews.Add(alternateView);

        var client = new SmtpClient();

        client.Send(message);
    }
}

Answer 3

If you Base64 encode the content, then you can break up the content into however many lines you want.

Answer 4

You're getting into dangerous territory attempting to parse HTML with a replace function. The easiest method would be to just display a warning box on the form that tells the user that lines cannot be longer than 1000 characters, and return an error message if they attempt to submit content with lines over that length.

Otherwise, you could insert a linebreak after X number of characters, and insert some special markup (like <!--AUTO-LINEBREAK-->, or similar) that informs whoever is receiving the e-mail that an automatic line break was inserted.

Answer 5

Hi,
Add normal line breaks where you think they should be. For example:

Off the top of my head, find all <p>, <table>, <tr>,<td>,<br>, and <div> tags and add a \r\n right before them.

Once that is done, loop through all the lines one more time. If there are any that are still 1000+ characters long, I would insert a \r\n in the whitespace.

Aslo, you should be removing any script tags from the HTML email body. Having script tags can cause all types of problems (marked as spam, marked as a virus, blocked, etc..).

hth,
Dave