Question

I’m currently building a web-server which can receive request, and send back a response.
I’ve managed to embed a port of Google’s v8 JavaScript engine to c# (javascript.net) to my project and I want to parse a requested file and run the server-sided JavaScript code that in it. I decided that this code will be contained inside a 2-character brackets, <: for opening and :> for closing. I started to parse it with code I written but after encountering some problems which made the code more messy and probably not very efficient I decided to go ahead and try using RegEx (I had you study it because I’ve never used it before). BUT WAIT. After talking to my friend about it he send me this post RegEx match open tags except XHTML self-contained tags I understood that it isn’t a good idea…
So my question is, How do I parse such thing? (Taking efficiency and clean code into account, after all it’s a webserver).
Thanks in advance!

Answer 1

Ideally, what you’d want to do is hook into V8’s lexer so you don’t end up catching things inside of strings and such. I looked at the source to that .NET wrapper, however, and it looks like it doesn’t allow that much customization. Instead, you may want to create a small state machine. You’d probably want at least these states:

• Literal data (for stuff outside of your <: and :> tags)
• Left angle bracket (for once you’ve consumed a < and are waiting for a potential :)
• Script state (for stuff inside of your <: and :> tags)
• Script double-quote string state
• Script double-quote string escape state
• Script single-quote string state
• Script single-quote string escape state
• Script slash state (for comments and regular expressions¹)
• Script line comment state
• Script block comment state
• Script block comment star state
• Script regular expression state
• Script colon state (for when you’ve encountered a : and are unsure whether a > or something else is next)

It may not be so quick to write as a regular expression, but it would be able to handle code like this:

Hello, world!
<:
    document.write("At least you won't think the script :> ends there.");
:>

¹On second thought, it’s probably not so easy to detect regular expressions.