Restore SEBPatch

SafeExamBrowser.SystemComponents/Registry/Registry.cs

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+/*
+ * Copyright (c) 2024 ETH Zürich, IT Services
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Timers;
+using Microsoft.Win32;
+using SafeExamBrowser.Logging.Contracts;
+using SafeExamBrowser.SystemComponents.Contracts.Registry;
+using SafeExamBrowser.SystemComponents.Contracts.Registry.Events;
+
+namespace SafeExamBrowser.SystemComponents.Registry
+{
+	public class Registry : IRegistry
+	{
+		private const int ONE_SECOND = 1000;
+
+		private readonly ILogger logger;
+		private readonly ConcurrentDictionary<(string key, string name), object> values;
+
+		private Timer timer;
+
+		public event RegistryValueChangedEventHandler ValueChanged;
+
+		public Registry(ILogger logger)
+		{
+			this.logger = logger;
+			this.values = new ConcurrentDictionary<(string key, string name), object>();
+		}
+
+		public void StartMonitoring(string key, string name)
+		{
+			if (timer?.Enabled != true)
+			{
+				timer = new Timer(ONE_SECOND);
+				timer.AutoReset = true;
+				timer.Elapsed += Timer_Elapsed;
+				timer.Start();
+			}
+
+			var success = TryRead(key, name, out var value);
+
+			values.TryAdd((key, name), value);
+
+			if (success)
+			{
+				logger.Debug($"Started monitoring value '{name}' from registry key '{key}'. Initial value: '{value}'.");
+			}
+			else
+			{
+				logger.Debug($"Started monitoring value '{name}' from registry key '{key}'. Value does currently not exist or initial read failed.");
+			}
+		}
+
+		public void StopMonitoring()
+		{
+			values.Clear();
+
+			if (timer != null)
+			{
+				timer.Stop();
+				logger.Debug("Stopped monitoring the registry.");
+			}
+		}
+
+		public void StopMonitoring(string key, string name)
+		{
+			values.TryRemove((key, name), out _);
+		}
+
+		public bool TryRead(string key, string name, out object value)
+		{
+			var defaultValue = new object();
+
+			value = default;
+
+			try
+			{
+				value = Microsoft.Win32.Registry.GetValue(key, name, defaultValue);
+			}
+			catch (Exception e)
+			{
+				logger.Error($"Failed to read value '{name}' from registry key '{key}'!", e);
+			}
+
+			return value != default && value != defaultValue;
+		}
+
+		public bool TryGetNames(string keyName, out IEnumerable<string> names)
+		{
+			names = default;
+
+			if (TryOpenKey(keyName, out var key))
+			{
+				using (key)
+				{
+					try
+					{
+						names = key.GetValueNames();
+					}
+					catch (Exception e)
+					{
+						logger.Error($"Failed to get registry value names for '{keyName}'!", e);
+					}
+				}
+			}
+			else
+			{
+				logger.Warn($"Failed to get names for '{keyName}'.");
+			}
+
+			return names != default;
+		}
+
+		public bool TryGetSubKeys(string keyName, out IEnumerable<string> subKeys)
+		{
+			subKeys = default;
+
+			if (TryOpenKey(keyName, out var key))
+			{
+				using (key)
+				{
+					try
+					{
+						subKeys = key.GetSubKeyNames();
+					}
+					catch (Exception e)
+					{
+						logger.Error($"Failed to get registry sub key names for '{keyName}'!", e);
+					}
+				}
+			}
+			else
+			{
+				logger.Warn($"Failed to get sub keys for '{keyName}'.");
+			}
+
+			return subKeys != default;
+		}
+
+		private bool Exists(string key, string name)
+		{
+			var defaultValue = new object();
+			var value = default(object);
+
+			try
+			{
+				value = Microsoft.Win32.Registry.GetValue(key, name, defaultValue);
+			}
+			catch (Exception e)
+			{
+				logger.Error($"Failed to read value '{name}' from registry key '{key}'!", e);
+			}
+
+			return value != default && value != defaultValue;
+		}
+
+		private void Timer_Elapsed(object sender, ElapsedEventArgs e)
+		{
+			foreach (var item in values)
+			{
+				if (Exists(item.Key.key, item.Key.name))
+				{
+					if (TryRead(item.Key.key, item.Key.name, out var value))
+					{
+						if (!Equals(item.Value, value))
+						{
+							logger.Debug($"Value '{item.Key.name}' from registry key '{item.Key.key}' has changed from '{item.Value}' to '{value}'!");
+							ValueChanged?.Invoke(item.Key.key, item.Key.name, item.Value, value);
+						}
+					}
+					else
+					{
+						logger.Error($"Failed to monitor value '{item.Key.name}' from registry key '{item.Key.key}'!");
+					}
+				}
+			}
+		}
+
+		private bool TryOpenKey(string keyName, out RegistryKey key)
+		{
+			key = default;
+
+			try
+			{
+				if (TryGetHiveForKey(keyName, out var hive))
+				{
+					if (keyName == hive.Name)
+					{
+						key = hive;
+					}
+					else
+					{
+						key = hive.OpenSubKey(keyName.Replace($@"{hive.Name}\", ""));
+					}
+				}
+				else
+				{
+					logger.Warn($"Failed to get hive for key '{keyName}'!");
+				}
+			}
+			catch (Exception e)
+			{
+				logger.Error($"Failed to open registry key '{keyName}'!", e);
+			}
+
+			return key != default;
+		}
+
+		private bool TryGetHiveForKey(string keyName, out RegistryKey hive)
+		{
+			var length = keyName.IndexOf('\\');
+			var name = length != -1 ? keyName.Substring(0, length).ToUpperInvariant() : keyName.ToUpperInvariant();
+
+			hive = default;
+
+			switch (name)
+			{
+				case "HKEY_CLASSES_ROOT":
+					hive = Microsoft.Win32.Registry.ClassesRoot;
+					break;
+				case "HKEY_CURRENT_CONFIG":
+					hive = Microsoft.Win32.Registry.CurrentConfig;
+					break;
+				case "HKEY_CURRENT_USER":
+					hive = Microsoft.Win32.Registry.CurrentUser;
+					break;
+				case "HKEY_LOCAL_MACHINE":
+					hive = Microsoft.Win32.Registry.LocalMachine;
+					break;
+				case "HKEY_PERFORMANCE_DATA":
+					hive = Microsoft.Win32.Registry.PerformanceData;
+					break;
+				case "HKEY_USERS":
+					hive = Microsoft.Win32.Registry.Users;
+					break;
+			}
+
+			return hive != default;
+		}
+	}
+}