SendIpcMessage under Win9X

zcecil · Post by **zcecil** » Mon Oct 04, 2004 9:56 am

I have a problem using SendIpcMessage under win9x.(the same code works under windows 2k/xp)
The hook dll:

typedef struct LFAStruct {
		BYTE type;
		CHAR from[4096+1];
		CHAR to[4096+1];
} *PLFAStruct;

bool SomeFunction( BYTE type, LPCSTR from, LPCSTR to )
{
	LFAStruct lfa;
	lfa.type = type;
	lstrcpynA( lfa.from, from, 4096);
	lstrcpynA( lfa.to, to, 4096);

	SendIpcMessage( "IPCNAME", &lfa, sizeof(lfa));

	return true;

}

the receiving app

Code: Select all

typedef struct LFAStruct {
		BYTE type;
		CHAR from[4096+1];
		CHAR to[4096+1];
} *PLFAStruct;

void WINAPI IpcHandler(LPSTR  pIpc,
                                PVOID   pMessageBuf,
                                UINT   dwMessageLen,
                                PVOID   pAnswerBuf,
                                UINT   dwAnswerLen)
{
    PLFAStruct lfa = (PLFAStruct)pMessageBuf;
    AnsiString msg ="[ipc]:[";
    msg = msg + lfa->from + "][";
    msg = msg + lfa->to + "]";
    Form1->Memo1->Lines->Add(msg);
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    if( !CreateIpcQueue( "IPCNAME", IpcHandler) ) {
        ShowMessage("create ipc queue failed");
        return;
    }

    InjectLibrary( ALL_SESSIONS | SYSTEM_PROCESSES, "hookdll.dll");
}

But the application can not receive anything from dll

Post by **madshi** » Tue Oct 05, 2004 6:32 am

Your IPC callback in the exe is called in the context of a secondary thread. The VCL is not thread safe. So using VCL in there seems dangerous to me. Anyway, I'm not sure whether that is the real problem.

Does your application freeze? Or do the IPC messages simply seem to get lost?

zcecil · Post by **zcecil** » Tue Oct 05, 2004 11:09 am

It does not freeze, the IPCHandler just doesn't get called.

Post by **madshi** » Tue Oct 05, 2004 12:23 pm

What happens if you reduce the IPC packet size? Win9x doesn't like too big IPC messages.

zcecil · Post by **zcecil** » Fri Oct 08, 2004 2:44 am

Thanks, it worked wher I reduce the IPC packet size

zcecil · Post by **zcecil** » Thu Oct 14, 2004 2:14 pm

sorry, problem again, this time it is under win xp.

i wrote a service program( running as LocalSystem) which inject the hook dll system-wide.
Then the service runs the application which CreateIpcQueue and waits for the dll to SendIpcMessage.

However, the application doesn't seem to receive anything from the dll.
I've tried running the application myself( as interactive user, local administrator), and it CAN receive ipc messages.

How can I fix this problem?
Thanks in advance.

Post by **madshi** » Thu Oct 14, 2004 2:35 pm

So you mean if that application is started from your service, then it doesn't work. But if you start it manually, then it does work? How do you know that it doesn't work? Are you logging the IPC message to a file or are you relying on message boxes?

zcecil · Post by **zcecil** » Fri Oct 15, 2004 1:53 am

Yes, I ShowMessage when the IPC handler is called, and I will log the messages to some files. I got no popup dialogs and no logs when the application is started from my service, but when I started it manually, it worked fine.

Post by **madshi** » Fri Oct 15, 2004 6:27 am

When your service starts the application, the app will most likely not run on the current desktop. So if you call ShowMessage there, the box will be invisible and nobody will close it. Get rid of those boxes, then it will probably work.