This repository contains the source code and Makefile necessary to compile the IExaDemo Local COM Server. This COM server is the base playground for our blog article https://blog.exatrack.com/STUBborn/ about DCOM & ALPC.

It can also be of use for anyone looking to develop a working COM server in C and explore the inner working of LRPC/DCOM in a local computer. This project also aims to be a good example of a standalone Makefile for COM server & proxy compilation from the .idl and .c implementation files. The code should compile in both 32 bits & 64 bits.

A simple python client is also provided in client.py as an example of use.

This code exposes the IExaDemo interface (45786100-1111-2222-3333-445500000001) and should be installed as a EXA_DEMO_SRV_CLSID (45786100-4343-4343-4343-434343434343).

This project is meant to be compiled (and was tested) with VCForPython27.msi (Microsoft Visual C++ Compiler for Python 2.7 9.0.0.30729). This package is a good way to install a fully working Windows compilation chain without any heavy IDE & visual studio package :)

VCForPython27.msi (sha256: 070474DB76A2E625513A5835DF4595DF9324D820F9CC97EAB2A596DCBC2F5CBF) can be found here : https://github.com/ExaTrack/COM_IExaDemo/releases/download/VCForPython27-publish/VCForPython27.msi

Once installed, the x64 environment can be started from a cmd.exe with the command line:

cmd.exe /k "%LOCALAPPDATA%\Programs\Common\Microsoft\Visual C++ for Python\9.0\vcvarsall.bat" x64

Example:

cmd> cmd.exe /k "%LOCALAPPDATA%\Programs\Common\Microsoft\Visual C++ for Python\9.0\vcvarsall.bat" x64
Setting environment for using Microsoft Visual Studio 2008 x64 tools.
cmd>

The server and proxy DLL can then be compiled by launching nmake from the project directory in the previously open cmd.

Example:

C:\Users\WDAGUtilityAccount\Desktop\COM_IExaDemo>nmake

Microsoft (R) Program Maintenance Utility Version 9.00.30729.01
Copyright (C) Microsoft Corporation.  All rights reserved.

        midl /out .\dist\amd64 src\iexademo.idl
[...]
Generated .\dist\amd64\IExaDemo_server_64.exe
Generated .\dist\amd64\IExaDemo_proxy_64.dll

The same thing can be done for a 32bits client & proxy dll with the following initial cmd.exe command line:

cmd.exe /k "%LOCALAPPDATA%\Programs\Common\Microsoft\Visual C++ for Python\9.0\vcvarsall.bat" x86

In this case : the resulting files will be:

• .\dist\x86\IExaDemo_server_32.exe
• .\dist\x86\IExaDemo_proxy_32.dll

The makefile also offers the following rules:

• nmake server to only compile the server
• nmake proxy to only compile the proxy DLL

The default rule of the makefile (all) only build the binaries. Three other rules allow installing them from the makefile:

• nmake install_server to install the server via reg add
• nmake install_proxy to install the proxy DLL with regsrv32
• nmake install to install both

The installation must be done in an administrator shell, as it will write to HKEY_CLASS_ROOT.

Question: If someone knows how to generate a proxy DLL with a DllRegisterServer method using HKEY_CURRENT_USER, I would be glad to have some feedback !

To test the python COM client, a version of Python should be installed (2.7 or 3.6+) as well as PythonForWindows. This module can be installed using py -m pip install PythonForWindows.

The client can then be tested using:

py client.py

The code output should look like:

COM_IExaDemo> py client.py
CreateInstance 45786100-4343-4343-4343-434343434343
    OK: Got an IUnknown: <IUnknown at 0x1bb11c1d948>
QueryInterface: IExaDemo.IID: 45786100-1111-2222-3333-445500000001
    OK: <IExaDemo at 0x1bb11c1dbc8>
Adding stuff:
    iexademo.add(0x41414141, 0x01010101) == 0x42424242

Another window (The IExaDemo_server.exe one) should pop-up and print a lot of stuff :) If this doesn't work, check that your python bitness match the bitness of the proxy DLL you compiled and installed.

The interface presented by the COM server, directly inherit IUnknown and present two additional methods:

HRESULT add(
    [in] unsigned int x,
    [in] unsigned int y,
    [out] unsigned int *res
);

HRESULT print(
    [in][string] wchar_t* msg);

Calling these methodes from any COM client should result in some debug priting in the server console.

Example entered at the end of py -i client.py:

# Python
>>> iexademo.add(0x12345678, 0x11111111, result)
# IExaDemo_server.exe OUTPUT:
CALL:IExaDemoImplem_add
[IExaDemoImplem_add] 0x12345678 + 0x11111111 = 0x23456789

# Python
>>> iexademo.print("My string parameter !")
67372036
# IExaDemo_server.exe OUTPUT:
CALL:IExaDemoImplem_print
[IExaDemoImplem_print] Msg: <My string parameter !>

• https://learn.microsoft.com/en-us/windows/win32/com/registering-com-servers
• https://learn.microsoft.com/en-us/previous-versions/windows/desktop/automat/hello-sample
• https://www.codeproject.com/Articles/8679/Building-a-LOCAL-COM-Server-and-Client-A-Step-by-S
• https://www.codeproject.com/Articles/13601/COM-in-plain-C#CLASS
• https://github.com/hakril/PythonForWindows