Drop/Rewrite/Generate Keyboard Events Under Linux

Excluding some keys from XGrabKeyboard

I don't think there's a way to do it. None of the mechanisms work quite how you would need them to.

Approach 1 is sort of what the window manager does if it decides not to intercept a click or key for example. However, the WM is using "passive" grabs on particular keys (XGrabKey=passive XGrabKeyboard=active) and then XAllowEvents(). XAllowEvents() does not work with XGrabKeyboard(). also, when you XAllowEvents with one of the Replay modes, the replayed event bypasses all passive grabs on the window that had the original grab and on all its parent windows. The WM's grabs will be on the root window which will always be a parent so there is no way to replay to the root window, best I can tell. Doing XGrabKey on every possible key would be sort of psycho anyhow.

Approach 2 would have bad race condition problems, because other key and mouse events could be processed before you could resend, so you'd reorder keys and send events to destroyed windows and other confusion. Also, there is no good way to send a key event. XSendEvent() is ignored by many clients (it sets a send_event flag in the event allowing this). XTest extension can be used but may be disabled on production X servers and still has race condition issues.

What you probably would need is a protocol extension that let you do an AllowEvents(mode=ReplayKeyboard) after a GrabKeyboard and without bypassing passive grabs on parent windows.

One caveat is that I don't know all the wild stuff that can be done with XKB and XInput2, so maybe there's something in those extensions.

Anyway, as far as I know you have to settle for the "escape key," though it might be nice eventually for the X server and/or the window manager specs to have "VMWare/VNC-type-thing awareness," that won't help you in the short term. An EWMH spec extension could be as simple as a new _NET_WM_WINDOW_TYPE for vnc/vmware/stuff-like-that and the window manager could reduce its keybindings or add an extra modifier to them or something when that window was focused, for example.

al sending fake keyboard events, whitespace issues

I just created my own translation function as you had suggested:

switch (hello[i])
{
case ' ':
XTestFakeKeyEvent(dis, 65, True, 0);
XTestFakeKeyEvent(dis, 65, False, 0);

as for capital letters, I used a shift key with the regular key:

case 'T':
XTestFakeKeyEvent(dis, 50, True, 0);
XTestFakeKeyEvent(dis, 28, True, 0);
XTestFakeKeyEvent(dis, 28, False, 0);
XTestFakeKeyEvent(dis, 50, False, 0);
break;

and special characters:

case '\n':
XTestFakeKeyEvent(dis, 36, True, 0);
XTestFakeKeyEvent(dis, 36, False, 0);
break;

things are working fine now, thanks Ishay

How to generate keyboard events?

It can be done using ctypes:

import ctypes
from ctypes import wintypes
import time

user32 = ctypes.WinDLL('user32', use_last_error=True)

INPUT_MOUSE    = 0
INPUT_KEYBOARD = 1
INPUT_HARDWARE = 2

KEYEVENTF_EXTENDEDKEY = 0x0001
KEYEVENTF_KEYUP       = 0x0002
KEYEVENTF_UNICODE     = 0x0004
KEYEVENTF_SCANCODE    = 0x0008

MAPVK_VK_TO_VSC = 0

# msdn.microsoft.com/en-us/library/dd375731
VK_TAB  = 0x09
VK_MENU = 0x12

# C struct definitions

wintypes.ULONG_PTR = wintypes.WPARAM

class MOUSEINPUT(ctypes.Structure):
    _fields_ = (("dx",          wintypes.LONG),
                ("dy",          wintypes.LONG),
                ("mouseData",   wintypes.DWORD),
                ("dwFlags",     wintypes.DWORD),
                ("time",        wintypes.DWORD),
                ("dwExtraInfo", wintypes.ULONG_PTR))

class KEYBDINPUT(ctypes.Structure):
    _fields_ = (("wVk",         wintypes.WORD),
                ("wScan",       wintypes.WORD),
                ("dwFlags",     wintypes.DWORD),
                ("time",        wintypes.DWORD),
                ("dwExtraInfo", wintypes.ULONG_PTR))

    def __init__(self, *args, **kwds):
        super(KEYBDINPUT, self).__init__(*args, **kwds)
        # some programs use the scan code even if KEYEVENTF_SCANCODE
        # isn't set in dwFflags, so attempt to map the correct code.
        if not self.dwFlags & KEYEVENTF_UNICODE:
            self.wScan = user32.MapVirtualKeyExW(self.wVk,
                                                 MAPVK_VK_TO_VSC, 0)

class HARDWAREINPUT(ctypes.Structure):
    _fields_ = (("uMsg",    wintypes.DWORD),
                ("wParamL", wintypes.WORD),
                ("wParamH", wintypes.WORD))

class INPUT(ctypes.Structure):
    class _INPUT(ctypes.Union):
        _fields_ = (("ki", KEYBDINPUT),
                    ("mi", MOUSEINPUT),
                    ("hi", HARDWAREINPUT))
    _anonymous_ = ("_input",)
    _fields_ = (("type",   wintypes.DWORD),
                ("_input", _INPUT))

LPINPUT = ctypes.POINTER(INPUT)

def _check_count(result, func, args):
    if result == 0:
        raise ctypes.WinError(ctypes.get_last_error())
    return args

user32.SendInput.errcheck = _check_count
user32.SendInput.argtypes = (wintypes.UINT, # nInputs
                             LPINPUT,       # pInputs
                             ctypes.c_int)  # cbSize

# Functions

def PressKey(hexKeyCode):
    x = INPUT(type=INPUT_KEYBOARD,
              ki=KEYBDINPUT(wVk=hexKeyCode))
    user32.SendInput(1, ctypes.byref(x), ctypes.sizeof(x))

def ReleaseKey(hexKeyCode):
    x = INPUT(type=INPUT_KEYBOARD,
              ki=KEYBDINPUT(wVk=hexKeyCode,
                            dwFlags=KEYEVENTF_KEYUP))
    user32.SendInput(1, ctypes.byref(x), ctypes.sizeof(x))

def AltTab():
    """Press Alt+Tab and hold Alt key for 2 seconds
    in order to see the overlay.
    """
    PressKey(VK_MENU)   # Alt
    PressKey(VK_TAB)    # Tab
    ReleaseKey(VK_TAB)  # Tab~
    time.sleep(2)
    ReleaseKey(VK_MENU) # Alt~

if __name__ == "__main__":
    AltTab()

hexKeyCode is the virtual keyboard mapping as defined by the Windows API. The list of codes is available on MSDN: Virtual-Key Codes (Windows)

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