PyXPCOM^? Hacking

First goal: get to the repository from inside xpcshell

xpcshell is the javascript equivalent of running python from the command line - you get a little interactive shell. From there, you can get to any XPCOM-enabled components like this:

js> c = Components.classes["componentname"].createInstance()
(... information about the component ... )
js> 

My goal was to be able to open the chandler repository from xpcshell

Building mozilla against our python turned out to be a little tricky. The irony was in the end I think all I really needed was the ActiveState^? Python, with our Python directory.

Once mozilla was built, the challenge was getting it to see our python. It seems that the ActiveState^? Python in c:\windows\system32\python24.dll is the one that will be seen by mozilla's dist\bin\components\pyloader.dll, because the windows search path involves looking first in the windows directory first before checking the PATH environment variable.

I hacked the hell out of the loader to get it to load out library, but to no avail. Finally I renamed c:\windows\system32\python24.dll and managed to get it to load our python24.dll. Then the problem is that Python itself has no way to know where its home is, so I had to set PYTHONHOME to chandler\release\bin. (setting PYTHONPATH did not help here) I'm guessing there's a way to do this with Py_Initialize or something.

In the end, it turned out that the ActiveState^? python24.dll works fine with our PYTHONHOME.

From there I set up some XPCOM components to allow me to get to python from JavaScript. First, nsIChandler.idl:

interface nsIChandler {
  void start();
};

Next, a python implementation:

import sys
sys.path.append('c:\alecf\tip\chandler\chandler');
sys.path.append('c:\alecf\tip\chandler\chandler\parcels');

from code import interact

class ChandlerMain:
    _com_interfaces_ = components.interfaces.nsIChandler
    _reg_clsid_ = "{9d6499dd-61b4-4510-9f33-0ad4a6cf6f41}"
    _reg_contractid_ = "Chandler"

    def start(self):
        interact()

I dumped this file in the components directory in mozilla.

Finally, I fired up xpcshell:

js> chandler = Components.classes["Chandler"].createInstance()
js> chandler.start()
Python 2.4.1 (#65, Mar 30 2005, 09:33:37) [MSC v.1310 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>>

Tada! Python running embedded inside of xpcshell, with full access to Chandler's repository!

I had to inherit from nsISupports to get my interface to work...

-- BrendanOConnor - 19 Aug 2005