128 lines
3.4 KiB
C#
128 lines
3.4 KiB
C#
/*
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* Copyright (c) 2024 ETH Zürich, IT Services
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*/
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using System;
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using System.Runtime.InteropServices;
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using SafeExamBrowser.WindowsApi.Constants;
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using SafeExamBrowser.WindowsApi.Contracts.Events;
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using SafeExamBrowser.WindowsApi.Delegates;
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using SafeExamBrowser.WindowsApi.Types;
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namespace SafeExamBrowser.WindowsApi.Hooks
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{
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internal class KeyboardHook
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{
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private bool altPressed, ctrlPressed;
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private KeyboardHookCallback callback;
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private IntPtr handle;
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private HookDelegate hookDelegate;
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internal Guid Id { get; private set; }
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internal KeyboardHook(KeyboardHookCallback callback)
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{
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this.callback = callback;
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this.Id = Guid.NewGuid();
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}
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internal void Attach()
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{
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var process = System.Diagnostics.Process.GetCurrentProcess();
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var module = process.MainModule;
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var moduleHandle = Kernel32.GetModuleHandle(module.ModuleName);
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// IMPORTANT:
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// Ensures that the hook delegate does not get garbage collected prematurely, as it will be passed to unmanaged code.
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// Not doing so will result in a <c>CallbackOnCollectedDelegate</c> error and subsequent application crash!
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hookDelegate = new HookDelegate(LowLevelKeyboardProc);
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handle = User32.SetWindowsHookEx(HookType.WH_KEYBOARD_LL, hookDelegate, moduleHandle, 0);
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}
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internal bool Detach()
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{
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return User32.UnhookWindowsHookEx(handle);
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}
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private IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam)
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{
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if (nCode >= 0)
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{
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var keyData = (KBDLLHOOKSTRUCT) Marshal.PtrToStructure(lParam, typeof(KBDLLHOOKSTRUCT));
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var modifier = GetModifiers(keyData, wParam.ToInt32());
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var state = GetState(wParam.ToInt32());
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if (callback((int) keyData.KeyCode, modifier, state))
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{
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return (IntPtr) 1;
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}
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}
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return User32.CallNextHookEx(handle, nCode, wParam, lParam);
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}
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private KeyState GetState(int wParam)
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{
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switch (wParam)
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{
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case Constant.WM_KEYDOWN:
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case Constant.WM_SYSKEYDOWN:
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return KeyState.Pressed;
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case Constant.WM_KEYUP:
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case Constant.WM_SYSKEYUP:
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return KeyState.Released;
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default:
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return KeyState.Unknown;
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}
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}
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private KeyModifier GetModifiers(KBDLLHOOKSTRUCT keyData, int wParam)
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{
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var modifier = KeyModifier.None;
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TrackCtrlAndAlt(keyData, wParam);
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if (altPressed || keyData.Flags.HasFlag(KBDLLHOOKSTRUCTFlags.LLKHF_ALTDOWN))
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{
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modifier |= KeyModifier.Alt;
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}
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if (ctrlPressed)
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{
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modifier |= KeyModifier.Ctrl;
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}
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return modifier;
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}
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private void TrackCtrlAndAlt(KBDLLHOOKSTRUCT keyData, int wParam)
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{
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var keyCode = keyData.KeyCode;
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if (keyCode == (uint) VirtualKeyCode.LeftControl || keyCode == (uint) VirtualKeyCode.RightControl)
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{
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ctrlPressed = IsPressed(wParam);
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}
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else if (keyCode == (uint) VirtualKeyCode.LeftAlt || keyCode == (uint) VirtualKeyCode.RightAlt)
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{
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altPressed = IsPressed(wParam);
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}
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if (ctrlPressed && altPressed && keyCode == (uint) VirtualKeyCode.Delete)
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{
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// When the Secure Attention Sequence is pressed, the WM_KEYUP / WM_SYSKEYUP messages for CTRL and ALT get lost...
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ctrlPressed = false;
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altPressed = false;
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}
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}
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private bool IsPressed(int wParam)
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{
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return wParam == Constant.WM_KEYDOWN || wParam == Constant.WM_SYSKEYDOWN;
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}
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}
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}
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