Accessing unregistered COM objects from python via a registered TLB

Question

I have three pieces of code that i'm working with at the moment:

• A closed source application (Main.exe)
• A closed source VB COM object implemented as a dll (comobj.dll)
• Code that I am developing in Python

comobj.dll hosts a COM object (lets say, 'MainInteract') that I would like to use from Python. I can already use this object perfectly fine from IronPython, but due to other requirements I need to use it from regular Python. I believe the best method here is to use win32com, but I can't quite make any headway at all.

First, some working IronPython code:

import clr
import os
import sys

__dir__ = os.path.dirname(os.path.realpath(__file__))
sys.path.insert(0, __dir__)
sys.path.append(r"C:\Path\To\comobj.dll") #This is where the com object dll actually is

clr.AddReferenceToFileAndPath(os.path.join(__dir__, r'comobj_1_1.dll')) #This is the .NET interop assembly that was created automatically via SharpDevelop's COM Inspector

from comobj_1_1 import clsMainInteract

o = clsMainInteract()
o.DoStuff(True)

---

And now the code that I attempted in regular Python:

>>> import win32com.client
>>> win32com.client.Dispatch("{11111111-comobj_guid_i_got_from_com_inspector}")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python26\lib\site-packages\win32com\client\__init__.py", line 95, in Dispatch
    dispatch, userName = dynamic._GetGoodDispatchAndUserName(dispatch,userName,clsctx)
  File "C:\Python26\lib\site-packages\win32com\client\dynamic.py", line 104, in _GetGoodDispatchAndUserName
    return (_GetGoodDispatch(IDispatch, clsctx), userName)
  File "C:\Python26\lib\site-packages\win32com\client\dynamic.py", line 84, in _GetGoodDispatch
    IDispatch = pythoncom.CoCreateInstance(IDispatch, None, clsctx, pythoncom.IID_IDispatch)
 pywintypes.com_error: (-2147221164, 'Class not registered', None, None)

I have also attempted using the friendly name of the TLB:

>>> import win32com.client
>>> win32com.client.Dispatch("Friendly TLB Name I Saw")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python26\lib\site-packages\win32com\client\__init__.py", line 95, in Dispatch
dispatch, userName = dynamic._GetGoodDispatchAndUserName(dispatch,userName,clsctx)
  File "C:\Python26\lib\site-packages\win32com\client\dynamic.py", line 104, in _GetGoodDispatchAndUserName
return (_GetGoodDispatch(IDispatch, clsctx), userName)
  File "C:\Python26\lib\site-packages\win32com\client\dynamic.py", line 84, in _GetGoodDispatch
    IDispatch = pythoncom.CoCreateInstance(IDispatch, None, clsctx, pythoncom.IID_IDispatch)
pywintypes.com_error: (-2147221005, 'Invalid class string', None, None)

In fact, the only success I've had was this:

import pythoncom
tlb = pythoncom.LoadRegTypeLib("{11111111-comobj_guid_i_got_from_com_inspector}",1,1,0)
>>> tlb
<PyITypeLib at 0x00AD7D78 with obj at 0x0025EDF0>
>>> tlb.GetDocumentation(1)
(u'clsMainInteract', None, 0, None)

But i'm not sure how to go from there to getting an object. I think my problem is that I need to load the dll into my process and get it to register itself with my process's COM source, so I can properly CoCreateInstance / win32com.client.Dispatch() on it.

I have also seen Activation Contexts referenced, especially when talking about 'no registration COM', but typically in a sentences like "Windows will create a context for you if you specify the right stuff in your .manifest files". I'd like to avoid manifest files if possible, as one would be required in the same folder as the (closed source) COM object dll, and i'd rather not drop any files in that directory if I can avoid it.

Thanks for the help.

Answer 1

For a useful utility module that wraps the object-from-DLL case, as well as others, see https://gist.github.com/4219140

__all__ = (
    ####### Class Objects

    #CoGetClassObject - Normal, not wrapped
    'CoDllGetClassObject', #Get ClassObject from a DLL file

    ####### ClassFactory::CreateInstance Wrappers

    'CoCreateInstanceFromFactory', #Create an object via IClassFactory::CreateInstance
    'CoCreateInstanceFromFactoryLicenced', #Create a licenced object via IClassFactory2::CreateInstanceLic

    ###### Util

    'CoReleaseObject', #Calls Release() on a COM object

    ###### Main Utility Methods

    #'CoCreateInstance', #Not wrapped, normal call
    'CoCreateInstanceLicenced', #CoCreateInstance, but with a licence key

    ###### Hacky DLL methods for reg-free COM without Activation Contexts, manifests, etc
    'CoCreateInstanceFromDll', #Given a dll, a clsid, and an iid, create an object
    'CoCreateInstanceFromDllLicenced', #Given a dll, a clsid, an iid, and a license key, create an object
)

IID_IClassFactory2 = "{B196B28F-BAB4-101A-B69C-00AA00341D07}"

from uuid import UUID
from ctypes import OleDLL, WinDLL, c_ulong, byref, WINFUNCTYPE, POINTER, c_char_p, c_void_p
from ctypes.wintypes import HRESULT
import pythoncom
import win32com.client

import logging
log = logging.getLogger(__name__)


def _raw_guid(guid):
    """Given a string GUID, or a pythoncom IID, return the GUID laid out in memory suitable for passing to ctypes"""
    return UUID(str(guid)).bytes_le

proto_icf2_base = WINFUNCTYPE(HRESULT,
    c_ulong,
    c_ulong,
    c_char_p,
    c_ulong,
    POINTER(c_ulong),
)
IClassFactory2__CreateInstanceLic = proto_icf2_base(7, 'CreateInstanceLic', (
    (1, 'pUnkOuter'),
    (1 | 4, 'pUnkReserved'),
    (1, 'riid'),
    (1, 'bstrKey'),
    (2, 'ppvObj'),
    ), _raw_guid(IID_IClassFactory2))

#--------------------------------
#--------------------------------

def _pc_wrap(iptr, resultCLSID=None):
    #return win32com.client.__WrapDispatch(iptr)
    log.debug("_pc_wrap: %s, %s"%(iptr, resultCLSID))
    disp = win32com.client.Dispatch(iptr, resultCLSID=resultCLSID)
    log.debug("_pc_wrap: %s (%s)", disp.__class__.__name__, disp)
    return disp

def CoCreateInstanceFromFactory(factory_ptr, iid_interface=pythoncom.IID_IDispatch, pUnkOuter=None):
    """Given a factory_ptr whose interface is IClassFactory, create the instance of clsid_class with the specified interface"""
    ClassFactory = pythoncom.ObjectFromAddress(factory_ptr.value, pythoncom.IID_IClassFactory)
    i = ClassFactory.CreateInstance(pUnkOuter, iid_interface)
    return i

def CoCreateInstanceFromFactoryLicenced(factory_ptr, key, iid_interface=pythoncom.IID_IDispatch, pUnkOuter=None):
    """Given a factory_ptr whose interface is IClassFactory2, create the instance of clsid_class with the specified interface"""
    requested_iid = _raw_guid(iid_interface)

    ole_aut = WinDLL("OleAut32.dll")
    key_bstr = ole_aut.SysAllocString(unicode(key))
    try:
        obj = IClassFactory2__CreateInstanceLic(factory_ptr, pUnkOuter or 0, c_char_p(requested_iid), key_bstr)
        disp_obj = pythoncom.ObjectFromAddress(obj, iid_interface)
        return disp_obj
    finally:
        if key_bstr:
            ole_aut.SysFreeString(key_bstr)

#----------------------------------

def CoReleaseObject(obj_ptr):
    """Calls Release() on a COM object. obj_ptr should be a c_void_p"""
    if not obj_ptr:
        return
    IUnknown__Release = WINFUNCTYPE(HRESULT)(2, 'Release', (), pythoncom.IID_IUnknown)
    IUnknown__Release(obj_ptr)

#-----------------------------------

def CoCreateInstanceLicenced(clsid_class, key, pythoncom_iid_interface=pythoncom.IID_IDispatch, dwClsContext=pythoncom.CLSCTX_SERVER, pythoncom_wrapdisp=True, wrapas=None):
    """Uses IClassFactory2::CreateInstanceLic to create a COM object given a licence key."""
    IID_IClassFactory2 = "{B196B28F-BAB4-101A-B69C-00AA00341D07}"
    ole = OleDLL("Ole32.dll")
    clsid_class_raw = _raw_guid(clsid_class)
    iclassfactory2 = _raw_guid(IID_IClassFactory2)
    com_classfactory = c_void_p(0)

    ole.CoGetClassObject(clsid_class_raw, dwClsContext, None, iclassfactory2, byref(com_classfactory))
    try:
        iptr = CoCreateInstanceFromFactoryLicenced(
                factory_ptr = com_classfactory,
                key=key,
                iid_interface=pythoncom_iid_interface,
                pUnkOuter=None,
        )
        if pythoncom_wrapdisp:
            return _pc_wrap(iptr, resultCLSID=wrapas or clsid_class)
        return iptr
    finally:
        if com_classfactory:
            CoReleaseObject(com_classfactory)

#-----------------------------------------------------------
#DLLs

def CoDllGetClassObject(dll_filename, clsid_class, iid_factory=pythoncom.IID_IClassFactory):
    """Given a DLL filename and a desired class, return the factory for that class (as a c_void_p)"""
    dll = OleDLL(dll_filename)
    clsid_class = _raw_guid(clsid_class)
    iclassfactory = _raw_guid(iid_factory)
    com_classfactory = c_void_p(0)
    dll.DllGetClassObject(clsid_class, iclassfactory, byref(com_classfactory))
    return com_classfactory

def CoCreateInstanceFromDll(dll, clsid_class, iid_interface=pythoncom.IID_IDispatch, pythoncom_wrapdisp=True, wrapas=None):
    iclassfactory_ptr = CoDllGetClassObject(dll, clsid_class)
    try:
        iptr = CoCreateInstanceFromFactory(iclassfactory_ptr, iid_interface)
        if pythoncom_wrapdisp:
            return _pc_wrap(iptr, resultCLSID=wrapas or clsid_class)
        return iptr
    finally:
        CoReleaseObject(iclassfactory_ptr)

def CoCreateInstanceFromDllLicenced(dll, clsid_class, key, iid_interface=pythoncom.IID_IDispatch, pythoncom_wrapdisp=True, wrapas=None):
    iclassfactory2_ptr = CoDllGetClassObject(dll, clsid_class, iid_factory=IID_IClassFactory2)
    try:
        iptr = CoCreateInstanceFromFactoryLicenced(iclassfactory2_ptr, key, iid_interface)
        if pythoncom_wrapdisp:
            return _pc_wrap(iptr, resultCLSID=wrapas or clsid_class)
        return iptr
    finally:
        CoReleaseObject(iclassfactory2_ptr)

Answer 2

What I did to access Free Download Manager's type library was the following:

import pythoncom, win32com.client

fdm = pythoncom.LoadTypeLib('fdm.tlb')
downloads_stat = None

for index in xrange(0, fdm.GetTypeInfoCount()):
    type_name = fdm.GetDocumentation(index)[0]

    if type_name == 'FDMDownloadsStat':
        type_iid = fdm.GetTypeInfo(index).GetTypeAttr().iid
        downloads_stat = win32com.client.Dispatch(type_iid)
        break

downloads_stat.BuildListOfDownloads(True, True)
print downloads_stat.Download(0).Url

The code above will print the URL of the first download.