Hook on a HWND
-
Hello, I'm writting a C++ DLL Hook to read any message to any program, so I'm using SetWindowsHookEx(WH_CALLWNDPROC, CallWndProc, handleInstance, 0); Then, in my CallWndProc, I need to filter the data coming so I can read the messages from the window I want, but it's not working as expected. During my tests, I wanted to read the messages from the HWND 0x00020afa, so if I put in the CallWndProc:
LRESULT CALLBACK CallWndProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if(nCode < 0)
return CallNextHookEx(handleHook, nCode, wParam, lParam);CWPSTRUCT\* cwpstruct = (CWPSTRUCT\*)lParam; if((HWND)0x00020afa == cwpstruct->hwnd) { MessageBox(NULL, "TEST","LOL",MB\_OK); } return CallNextHookEx(handleHook, nCode, wParam, lParam);}
I would get the message boxes popping like crazy, but then I decided to add a global HWND to my dll:
HWND hWindow;And then a stupid function to set it:VOID __stdcall HookHwnd(HWND hWnd)
{
hWindow = hWnd;
}So I can choose which HWND i want to track with
if(hWindow == cwpstruct->hwnd)instead ofif((HWND)0x00020afa == cwpstruct->hwnd)... But it doesn't work. Am I doing something wrong here? I'm new to the dll world. Also, is this the correct way to read the messages from a window? Thanks! -
Hello, I'm writting a C++ DLL Hook to read any message to any program, so I'm using SetWindowsHookEx(WH_CALLWNDPROC, CallWndProc, handleInstance, 0); Then, in my CallWndProc, I need to filter the data coming so I can read the messages from the window I want, but it's not working as expected. During my tests, I wanted to read the messages from the HWND 0x00020afa, so if I put in the CallWndProc:
LRESULT CALLBACK CallWndProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if(nCode < 0)
return CallNextHookEx(handleHook, nCode, wParam, lParam);CWPSTRUCT\* cwpstruct = (CWPSTRUCT\*)lParam; if((HWND)0x00020afa == cwpstruct->hwnd) { MessageBox(NULL, "TEST","LOL",MB\_OK); } return CallNextHookEx(handleHook, nCode, wParam, lParam);}
I would get the message boxes popping like crazy, but then I decided to add a global HWND to my dll:
HWND hWindow;And then a stupid function to set it:VOID __stdcall HookHwnd(HWND hWnd)
{
hWindow = hWnd;
}So I can choose which HWND i want to track with
if(hWindow == cwpstruct->hwnd)instead ofif((HWND)0x00020afa == cwpstruct->hwnd)... But it doesn't work. Am I doing something wrong here? I'm new to the dll world. Also, is this the correct way to read the messages from a window? Thanks!Hi Tony_P Whenever you install a hook, the DLL gets injected into the process' memory. So, each process will have all together different global variable 'hWindow'. To avoid this you'll have to use the concept of data sharing among the DLLs/Process. Following links may help you. Data Sharing Among DLL/Process[^] Hooking Sample[^]
-Malli...! :rose:****
-
Hello, I'm writting a C++ DLL Hook to read any message to any program, so I'm using SetWindowsHookEx(WH_CALLWNDPROC, CallWndProc, handleInstance, 0); Then, in my CallWndProc, I need to filter the data coming so I can read the messages from the window I want, but it's not working as expected. During my tests, I wanted to read the messages from the HWND 0x00020afa, so if I put in the CallWndProc:
LRESULT CALLBACK CallWndProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if(nCode < 0)
return CallNextHookEx(handleHook, nCode, wParam, lParam);CWPSTRUCT\* cwpstruct = (CWPSTRUCT\*)lParam; if((HWND)0x00020afa == cwpstruct->hwnd) { MessageBox(NULL, "TEST","LOL",MB\_OK); } return CallNextHookEx(handleHook, nCode, wParam, lParam);}
I would get the message boxes popping like crazy, but then I decided to add a global HWND to my dll:
HWND hWindow;And then a stupid function to set it:VOID __stdcall HookHwnd(HWND hWnd)
{
hWindow = hWnd;
}So I can choose which HWND i want to track with
if(hWindow == cwpstruct->hwnd)instead ofif((HWND)0x00020afa == cwpstruct->hwnd)... But it doesn't work. Am I doing something wrong here? I'm new to the dll world. Also, is this the correct way to read the messages from a window? Thanks!Tony_P wrote:
Am I doing something wrong here?
Yes. Think of it this way... your DLL is being mapped into multiple applications each of which is executing inside its own Virtual Address Space[^]. This essentially means that each copy of the DLL has a different value for your global variable named hWindow. You need to implement a shared data section: How To Share Data Between Different Mappings of a DLL[^] This will allow all applications to read from the shared data section. Best Wishes, -David Delaune
-
Hi Tony_P Whenever you install a hook, the DLL gets injected into the process' memory. So, each process will have all together different global variable 'hWindow'. To avoid this you'll have to use the concept of data sharing among the DLLs/Process. Following links may help you. Data Sharing Among DLL/Process[^] Hooking Sample[^]
-Malli...! :rose:****
Even if each process has a different hWindow, wouldn't the function "HookHwnd" I created set every hWindow to the same value? Anyway, thank you for the links, I'm going to try this :)
-
Tony_P wrote:
Am I doing something wrong here?
Yes. Think of it this way... your DLL is being mapped into multiple applications each of which is executing inside its own Virtual Address Space[^]. This essentially means that each copy of the DLL has a different value for your global variable named hWindow. You need to implement a shared data section: How To Share Data Between Different Mappings of a DLL[^] This will allow all applications to read from the shared data section. Best Wishes, -David Delaune
Well it seems like this shared memory is the solution. I'm going to try it. Thank you!
-
Even if each process has a different hWindow, wouldn't the function "HookHwnd" I created set every hWindow to the same value? Anyway, thank you for the links, I'm going to try this :)
Tony_P wrote:
wouldn't the function "HookHwnd" I created set every hWindow to the same value
You could actually make it work this way. You use the RegisterWindowMessage Function[^] to create a unique window message and broadcast it using HWND_BROADCAST[^]. Just make sure that your window message is unique and its not in the WM_USER range so it will not conflict with custom window messages used internally in other applications. RegisterWindowMessage will return something in the range of MAXINTATOM-MAXWORD so you should be safe. In your DLL you could handle this custom message and set the local variable to a target window handle. And since you have both WPARAM and LPARAM this means you could target both PID and window handle. Essentially instructing the DLL "Process with PID x please monitor window n". This is a sort of hackish way of doing it in my opinion, the shared-data segment in my earlier post would probably be a better choice. You could instruct each DLL there also using a similar technique. The great thing about engineering software is there is always many paths to reach the goal. Best Wishes, -David Delaune
-
Tony_P wrote:
wouldn't the function "HookHwnd" I created set every hWindow to the same value
You could actually make it work this way. You use the RegisterWindowMessage Function[^] to create a unique window message and broadcast it using HWND_BROADCAST[^]. Just make sure that your window message is unique and its not in the WM_USER range so it will not conflict with custom window messages used internally in other applications. RegisterWindowMessage will return something in the range of MAXINTATOM-MAXWORD so you should be safe. In your DLL you could handle this custom message and set the local variable to a target window handle. And since you have both WPARAM and LPARAM this means you could target both PID and window handle. Essentially instructing the DLL "Process with PID x please monitor window n". This is a sort of hackish way of doing it in my opinion, the shared-data segment in my earlier post would probably be a better choice. You could instruct each DLL there also using a similar technique. The great thing about engineering software is there is always many paths to reach the goal. Best Wishes, -David Delaune
Wow! Thank you for sharing all this valuable information to me. Now back on Visual C++ :p