Monday, September 10, 2007

More fooling around with scripting

Over the weekend I wrote a scripting engine for windows in c#. It doesn't do anything yet, it just implements the scripting API. The only problem is that it doesn't completely work. It doesn't completely fail, either. That's weird because I'd expect an all or nothing response. When I run the script under the cscript host, it creates an instance of the engine and calls the SetScriptSite and InitNew methods. Then it craps out with an error `CScript Error: Can't find script engine "LScript" for script. I suspect the actual error message is a red herring. I bet that the engine initialization code is located in a try/catch/finally block and the message comes from that block. What is weird is that since the SetScriptSite and InitNew methods are being invoked, it is clear that a whole lot of the machinery is working. Clearly the CLR runtime is being loaded, the engine assembly is loaded, the engine class is created and the com-callable wrapper for both the IActiveScript and IActiveScriptParse interfaces is being correctly created and delivered to the script host. So why does it fail? I ran the server from two different hosts: CScript and from within Internet Explorer. Both seem to be able to call the first few methods. A hint is that the next method each should call is AddNamedItem. Neither host seems to invoke that. I can't see what cscript is trying to do (the stack trace is truncated), so I wrote my own scripting host in C++. Unfortunately it seems to work with no problem. I also tried Hugh Brown's NullScript engine, and that seems to work just fine, too. For a while I thought I was on to something because I noticed that a typelib that was being generated was missing some entries. It made no difference when I corrected the problem, though. In any case, I put the code up at and I'll probably play with it a bit more before I give up completely.