Real-Time Console Output Redirection

#define WIN32_LEAN_AND_MEAN		// Exclude rarely-used stuff from Windows headers
#include <windows.h>
#include <tchar.h>

/*
 Quick note: 
*/

#define SLEEP_TIME 50 // reactivity: sleep time to wait for subprocess to output some more data

CONST COORD origin = { 0, 0 };

// we should have been spawned using SW_HIDE, so our console window is not visible
int main(int argc, char* argv[])
{
	// get pipe/console to output to
	HANDLE hOutput = GetStdHandle(STD_OUTPUT_HANDLE);
	DWORD dwDummy;

	// parse command line : skip to RTconsole's arguments
	LPTSTR commandLine = GetCommandLine();
	if (*commandLine == '"')
		commandLine = _tcschr(commandLine+1, _T('"'));
	else
		commandLine = _tcspbrk(commandLine, _T(" \t"));
	if (!commandLine) return -1;
	commandLine += _tcsspn(commandLine+1, _T(" \t"))+1;
	if (commandLine[0] == '\0') return -1;

	// prepare the console window & inherited screen buffer
	SECURITY_ATTRIBUTES sa;
	sa.nLength = sizeof(sa);
	sa.lpSecurityDescriptor = NULL;
	sa.bInheritHandle = TRUE;
	HANDLE hConsole = CreateConsoleScreenBuffer(GENERIC_READ|GENERIC_WRITE,FILE_SHARE_READ|FILE_SHARE_WRITE,&sa,CONSOLE_TEXTMODE_BUFFER,NULL);
	FillConsoleOutputCharacter(hConsole, '\0', MAXLONG, origin, &dwDummy); // fill screen buffer with zeroes
	SetStdHandle(STD_OUTPUT_HANDLE, hConsole); // to be inherited by child process

	// start the subprocess
	PROCESS_INFORMATION pi;
	STARTUPINFO si;
	ZeroMemory(&si, sizeof(STARTUPINFO));
	si.cb = sizeof(STARTUPINFO);
	si.dwFlags = STARTF_FORCEOFFFEEDBACK; // we don't want the "app starting" cursor
	// all other default options are already good : we want subprocess to share the same console and to inherit our STD handles
	if (!CreateProcess(	NULL, commandLine, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi))
	{
		CloseHandle(hConsole);
		return -2;
	}
	CloseHandle(pi.hThread); // always close the hThread after a CreateProcess

	COORD lastpos = { 0, 0 };
	CONSOLE_SCREEN_BUFFER_INFO csbi;
	bool exitNow = false;
	do
	{
		if (WaitForSingleObject(pi.hProcess, 0) != WAIT_TIMEOUT)
			exitNow = true; // exit after this last iteration

		// get screen buffer state
		GetConsoleScreenBufferInfo(hConsole, &csbi);
		int lineWidth = csbi.dwSize.X;
		
		if ((csbi.dwCursorPosition.X == lastpos.X) && (csbi.dwCursorPosition.Y == lastpos.Y))
			Sleep(SLEEP_TIME); // text cursor did not move, sleep a while
		else
		{
			DWORD count = (csbi.dwCursorPosition.Y-lastpos.Y)*lineWidth+csbi.dwCursorPosition.X-lastpos.X;
			// read newly output characters starting from last cursor position
			LPTSTR buffer = (LPTSTR) LocalAlloc(0, count*sizeof(TCHAR));
			ReadConsoleOutputCharacter(hConsole, buffer, count, lastpos, &count);
			// fill screen buffer with zeroes
			FillConsoleOutputCharacter(hConsole, '\0', count, lastpos, &dwDummy);
			
			SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_TIME_CRITICAL);
			lastpos = csbi.dwCursorPosition;
			GetConsoleScreenBufferInfo(hConsole, &csbi);
			if ((csbi.dwCursorPosition.X == lastpos.X) && (csbi.dwCursorPosition.Y == lastpos.Y))
			{ // text cursor did not move since this treatment, hurry to reset it to home
				SetConsoleCursorPosition(hConsole, origin);
				lastpos = origin;
			}
			SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_NORMAL);

			// scan screen buffer and transmit character to real output handle
			LPTSTR scan = buffer;
			do
			{
				if (*scan)
				{
					DWORD len = 1;
					while (scan[len] && (len < count))
						len++;
					WriteFile(hOutput, scan, len, &dwDummy, NULL);
					scan += len;
					count -= len;
				}
				else
				{
					DWORD len = 1;
					while (!scan[len] && (len < count))
						len++;
					scan += len;
					count -= len;
					len = (len+lineWidth-1)/lineWidth;
					for (;len;len--)
						WriteFile(hOutput, "\r\n", 2, &dwDummy, NULL);
				}
			} while (count);
			//FlushFileBuffers(hOutput); // seems unnecessary
			LocalFree(buffer);
		}
		// loop until end of subprocess
	} while (!exitNow);
	
	CloseHandle(hConsole);
	
	// release subprocess handle
	DWORD exitCode;
	if (!GetExitCodeProcess(pi.hProcess, &exitCode))
		exitCode = -3;
	CloseHandle(pi.hProcess); 
	return exitCode;
}