Python Win32Gui automation - Send WM_COPYDATA to get data from BSPlayer

Question

I am desperately trying to automate BSPlayer from my script. I was successful in sending simple command ids to the BSPlayer window(volume up/down, play/pause, etc.), however I am not able to get the file name back.

Here is the BSPlayer API. I was able to emulate in python the first parts, however the WM_COPYDATA doesn't work.

Here is my Python code:

copyDataCmd = COPYDATASTRUCT()
copyDataCmd.dwData = self.BSP_GetFileName
copyDataCmd.lpData = ""
copyDataCmd.cbData = 4                
win32gui.SendMessage(self.playerWindowHandler, win32con.WM_COPYDATA, 
                     ownHandler, copyDataCmd);

Obviously .lpData returns "" ...

What I am trying to emulate:

cds:TCOPYDATASTRUCT; 
buf:array[0..MAX_PATH-1] of char; 
adr:pointer; // 
adr:=@buf; 
cds.dwData:=BSP_GetFileName; 
cds.lpData:=@adr; 
cds.cbData:=4; 
SendMessage(bsp_hand,WM_COPYDATA,appHWND,lParam(@cds)); 
// available in BSPlayer version 0.84.484+ // 
// appHWND is calling application window handle 
// File name will be copied to buf // 
// Get open file name 
BSP_GetFileName = $1010B;

To be more verbose, I am trying to get the filename from a BSPlayer window. For this I am trying to emulate the code above. I expect a buffer of some sort to be filled with my desired string, but it comes up empty. So, again, I want the Python equivalent of the code just above.

For example this code was emulated succesfully:

status := SendMessage(bsp_hand,WM_BSP_CMD,BSP_GetStatus,0); 
// available in BSPlayer version 0.84.484+ // 
// Return player status // 0 - STOP // 1 - PAUSE 
// 2 - PLAY // 4 - No movie   open        
BSP_GetStatus = $10102; 

Thanks in advance!

Answer 1

You cannot replicate that WM_COPYDATA in your Python code. It can only be used in-proc, for example for plugins.

The example Delphi code is written under the assumption that the call to WM_COPYDATA is made from the same process as the window which receives the message. That's because the WM_COPYDATA is used to copy a pointer, and pointers are only valid inside the process which allocated the memory. You cannot send a pointer across a process boundary.

In my opinion, the designers of the interface are abusing WM_COPYDATA. It is meant to be used to solve the exact problem of transferring data between processes. It is the simplest most lightweight inter-process communication available. To then use it to transfer a pointer rather defeats the process.