S22.Imap | NET library component for communicating with IMAP servers

You can read this blog post that explains what most C# MIME parsers get wrong and why MimeKit can handle multiple charset encodings.

https://jeffreystedfast.blogspot.com/2013/09/time-for-rant-on-mime-parsers.html https://jeffreystedfast.blogspot.com/2013/08/why-decoding-rfc2047-encoded-headers-is.html

Since the StackOverflow moderators will likely complain about posting a link, here's a copy & paste of the content:

Warning: Viewer discretion is advised.

Where should I begin?

I guess I should start by saying that I am obsessed with MIME and, in particular, MIME parsers. No, really. I am obsessed. Don't believe me? I've written and/or worked on several MIME parsers at this point. It started off in my college days working on Spruce which had a horrendously bad MIME parser, and so as you read farther along in my rant about shitty MIME parsers, keep in mind: I've been there, I've written a shitty MIME parser.

As a handful of people are aware, I've recently started implementing a C# MIME parser called MimeKit. As I work on this, I've been searching around on GitHub and Google to see what other MIME parsers exist out there to find out what sort of APIs they provide. I thought perhaps I'll find one that offers a well-designed API that will inspire me. Perhaps, by some miracle, I'd find one that was actually pretty good that I could just contribute to instead of writing my own from scratch (yea, wishful thinking). Instead, all I have found are poorly designed and implemented MIME parsers, many probably belong on the front page of the Daily WTF.

I guess I'll start with some softballs.

First, there's the fact that every single one of them were written as System.String parsers. Don't be fooled by the ones claiming to be "stream parsers", because all any of those did was to slap a TextReader on top of the byte stream and start using reader.ReadLine(). What's so bad about that, you ask? For those not familiar with MIME, I'd like for you to take a look at the raw email sources in your inboxes particularly if you have correspondence with anyone outside of the US. Hopefully most of your friends and colleagues are using more-or-less MIME compliant email clients, but I guarantee you'll find at least a few emails with raw 8bit text.

Now, if the language they were using was C or C++, they might be able to get away with doing this because they'd technically be operating on byte arrays, but with Java and C#, a 'string' is a unicode string. Tell me: how does one get a unicode string from a raw byte array?

Bingo. You need to know the charset before you can convert those bytes into unicode characters.

To be fair, there's really no good way of handling raw 8bit text in message headers, but by using a TextReader approach, you are really limiting the possibilities.

Next up is the ReadLine() approach. One of the 2 early parsers in GMime (pan-mime-parser.c back in the version 0.7 days) used a ReadLine() approach, so I understand the thinking behind this. And really, there's nothing wrong with this approach as far as correctness goes, it's more of a "this can never be fast" complaint. Of the two early parsers in GMime, the pan-mime-parser.c backend was horribly slow compared to the in-memory parser. Of course, that's not very surprising. More surprising to me at the time was that when I wrote GMime's current generation of parser (sometime between v0.7 and v1.0), it was just as fast as the in-memory parser ever was and only ever had up to 4k in a read buffer at any given time. My point is, there are far better approaches than ReadLine() if you want your parser to be reasonably performant... and why wouldn't you want that? Your users definitely want that.

Okay, now come the more serious problems that I encountered in nearly all of the mime parser libraries I found.

I think that every single mime parser I've found so far uses the "String.Split()" approach for parsing address headers and/or for parsing parameter lists on headers such as Content-Type and Content-Disposition.

Here's an example from one C# MIME parser: