[Hosts]Handle read-only hosts file (#29562)

* handle read-only hosts file

src/modules/Hosts/Hosts.Tests/HostsServiceTest.cs

@@ -5,6 +5,7 @@
 using System.IO.Abstractions.TestingHelpers;
 using System.Linq;
 using System.Threading.Tasks;
+using Hosts.Exceptions;
 using Hosts.Helpers;
 using Hosts.Models;
 using Hosts.Settings;
@@ -18,11 +19,13 @@ namespace Hosts.Tests
     [TestClass]
     public class HostsServiceTest
     {
+        private static Mock<IUserSettings> _userSettings;
         private static Mock<IElevationHelper> _elevationHelper;
 
         [ClassInitialize]
         public static void ClassInitialize(TestContext context)
         {
+            _userSettings = new Mock<IUserSettings>();
             _elevationHelper = new Mock<IElevationHelper>();
             _elevationHelper.Setup(m => m.IsElevated).Returns(true);
         }
@@ -31,8 +34,7 @@ namespace Hosts.Tests
         public void Hosts_Exists()
         {
             var fileSystem = new CustomMockFileSystem();
-            var userSettings = new Mock<IUserSettings>();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
-            var service = new HostsService(fileSystem, userSettings.Object, _elevationHelper.Object);
             fileSystem.AddFile(service.HostsFilePath, new MockFileData(string.Empty));
             var result = service.Exists();
 
@@ -43,8 +45,7 @@ namespace Hosts.Tests
         public void Hosts_Not_Exists()
         {
             var fileSystem = new CustomMockFileSystem();
-            var userSettings = new Mock<IUserSettings>();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
-            var service = new HostsService(fileSystem, userSettings.Object, _elevationHelper.Object);
             var result = service.Exists();
 
             Assert.IsFalse(result);
@@ -65,8 +66,7 @@ namespace Hosts.Tests
 ";
 
             var fileSystem = new CustomMockFileSystem();
-            var userSettings = new Mock<IUserSettings>();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
-            var service = new HostsService(fileSystem, userSettings.Object, _elevationHelper.Object);
             fileSystem.AddFile(service.HostsFilePath, new MockFileData(content));
 
             var data = await service.ReadAsync();
@@ -91,8 +91,7 @@ namespace Hosts.Tests
 ";
 
             var fileSystem = new CustomMockFileSystem();
-            var userSettings = new Mock<IUserSettings>();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
-            var service = new HostsService(fileSystem, userSettings.Object, _elevationHelper.Object);
             fileSystem.AddFile(service.HostsFilePath, new MockFileData(content));
 
             var data = await service.ReadAsync();
@@ -118,8 +117,7 @@ namespace Hosts.Tests
 ";
 
             var fileSystem = new CustomMockFileSystem();
-            var userSettings = new Mock<IUserSettings>();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
-            var service = new HostsService(fileSystem, userSettings.Object, _elevationHelper.Object);
             fileSystem.AddFile(service.HostsFilePath, new MockFileData(content));
 
             var data = await service.ReadAsync();
@@ -138,9 +136,7 @@ namespace Hosts.Tests
         public async Task Empty_Hosts()
         {
             var fileSystem = new CustomMockFileSystem();
-            var userSettings = new Mock<IUserSettings>();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
-
-            var service = new HostsService(fileSystem, userSettings.Object, _elevationHelper.Object);
             fileSystem.AddFile(service.HostsFilePath, new MockFileData(string.Empty));
 
             await service.WriteAsync(string.Empty, Enumerable.Empty<Entry>());
@@ -203,7 +199,6 @@ namespace Hosts.Tests
             var fileSystem = new CustomMockFileSystem();
             var userSettings = new Mock<IUserSettings>();
             userSettings.Setup(m => m.AdditionalLinesPosition).Returns(HostsAdditionalLinesPosition.Bottom);
-
             var service = new HostsService(fileSystem, userSettings.Object, _elevationHelper.Object);
             fileSystem.AddFile(service.HostsFilePath, new MockFileData(content));
 
@@ -228,8 +223,7 @@ namespace Hosts.Tests
 ";
 
             var fileSystem = new CustomMockFileSystem();
-            var userSettings = new Mock<IUserSettings>();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
-            var service = new HostsService(fileSystem, userSettings.Object, _elevationHelper.Object);
             fileSystem.AddFile(service.HostsFilePath, new MockFileData(content));
 
             var data = await service.ReadAsync();
@@ -243,12 +237,37 @@ namespace Hosts.Tests
         public async Task Save_NotRunningElevatedException()
         {
             var fileSystem = new CustomMockFileSystem();
-            var userSettings = new Mock<IUserSettings>();
             var elevationHelper = new Mock<IElevationHelper>();
             elevationHelper.Setup(m => m.IsElevated).Returns(false);
 
-            var service = new HostsService(fileSystem, userSettings.Object, elevationHelper.Object);
+            var service = new HostsService(fileSystem, _userSettings.Object, elevationHelper.Object);
             await Assert.ThrowsExceptionAsync<NotRunningElevatedException>(async () => await service.WriteAsync("# Empty hosts file", Enumerable.Empty<Entry>()));
         }
+
+        [TestMethod]
+        public async Task Save_ReadOnlyHostsException()
+        {
+            var fileSystem = new CustomMockFileSystem();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
+            var hostsFile = new MockFileData(string.Empty);
+            hostsFile.Attributes = System.IO.FileAttributes.ReadOnly;
+            fileSystem.AddFile(service.HostsFilePath, hostsFile);
+
+            await Assert.ThrowsExceptionAsync<ReadOnlyHostsException>(async () => await service.WriteAsync("# Empty hosts file", Enumerable.Empty<Entry>()));
+        }
+
+        [TestMethod]
+        public void Remove_ReadOnly()
+        {
+            var fileSystem = new CustomMockFileSystem();
+            var service = new HostsService(fileSystem, _userSettings.Object, _elevationHelper.Object);
+            var hostsFile = new MockFileData(string.Empty);
+            hostsFile.Attributes = System.IO.FileAttributes.ReadOnly;
+            fileSystem.AddFile(service.HostsFilePath, hostsFile);
+
+            service.RemoveReadOnly();
+            var readOnly = fileSystem.FileInfo.FromFileName(service.HostsFilePath).Attributes.HasFlag(System.IO.FileAttributes.ReadOnly);
+            Assert.IsFalse(readOnly);
+        }
     }
 }

src/modules/Hosts/Hosts/Exceptions/NotRunningElevatedException.cs

@@ -4,7 +4,7 @@
 
 using System;
 
-namespace Hosts.Helpers
+namespace Hosts.Exceptions
 {
     public class NotRunningElevatedException : Exception
     {

src/modules/Hosts/Hosts/Exceptions/ReadOnlyHostsException.cs

@@ -0,0 +1,12 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+namespace Hosts.Exceptions
+{
+    public class ReadOnlyHostsException : Exception
+    {
+    }
+}

src/modules/Hosts/Hosts/Helpers/HostsService.cs

@@ -13,6 +13,7 @@ using System.Net.NetworkInformation;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
+using Hosts.Exceptions;
 using Hosts.Models;
 using Hosts.Settings;
 using ManagedCommon;
@@ -129,6 +130,11 @@ namespace Hosts.Helpers
                 throw new NotRunningElevatedException();
             }
 
+            if (_fileSystem.FileInfo.FromFileName(HostsFilePath).IsReadOnly)
+            {
+                throw new ReadOnlyHostsException();
+            }
+
             var lines = new List<string>();
 
             if (entries.Any())
@@ -288,6 +294,15 @@ namespace Hosts.Helpers
             }
         }
 
+        public void RemoveReadOnly()
+        {
+            var fileInfo = _fileSystem.FileInfo.FromFileName(HostsFilePath);
+            if (fileInfo.IsReadOnly)
+            {
+                fileInfo.IsReadOnly = false;
+            }
+        }
+
         public void Dispose()
         {
             Dispose(disposing: true);

src/modules/Hosts/Hosts/Helpers/IHostsService.cs

@@ -24,5 +24,7 @@ namespace Hosts.Helpers
         void CleanupBackup();
 
         void OpenHostsFile();
+
+        void RemoveReadOnly();
     }
 }

src/modules/Hosts/Hosts/HostsXAML/Views/MainPage.xaml

@@ -377,7 +377,15 @@
                     IsOpen="{x:Bind ViewModel.Error, Mode=TwoWay}"
                     Message="{x:Bind ViewModel.ErrorMessage, Mode=TwoWay}"
                     Severity="Error"
-                    Visibility="{x:Bind ViewModel.Error, Mode=TwoWay, Converter={StaticResource BoolToVisibilityConverter}}" />
+                    Visibility="{x:Bind ViewModel.Error, Mode=TwoWay, Converter={StaticResource BoolToVisibilityConverter}}">
+                    <InfoBar.ActionButton>
+                        <Button
+                            x:Uid="MakeWritable"
+                            HorizontalAlignment="Right"
+                            Command="{x:Bind ViewModel.OverwriteHostsCommand}"
+                            Visibility="{x:Bind ViewModel.IsReadOnly, Mode=TwoWay, Converter={StaticResource BoolToVisibilityConverter}}" />
+                    </InfoBar.ActionButton>
+                </InfoBar>
                 <InfoBar
                     x:Uid="FileChanged"
                     Margin="0,8,0,0"
@@ -385,7 +393,10 @@
                     Severity="Informational"
                     Visibility="{x:Bind ViewModel.FileChanged, Mode=TwoWay, Converter={StaticResource BoolToVisibilityConverter}}">
                     <InfoBar.ActionButton>
-                        <Button x:Uid="Reload" Command="{x:Bind ViewModel.ReadHostsCommand}" />
+                        <Button
+                            x:Uid="Reload"
+                            HorizontalAlignment="Right"
+                            Command="{x:Bind ViewModel.ReadHostsCommand}" />
                     </InfoBar.ActionButton>
                 </InfoBar>
             </StackPanel>

src/modules/Hosts/Hosts/Strings/en-us/Resources.resw

@@ -228,6 +228,10 @@
     <value>The hosts file cannot be saved because the program isn't running as administrator.</value>
     <comment>"Hosts" refers to the system hosts file, do not loc</comment>
   </data>
+  <data name="FileSaveError_ReadOnly" xml:space="preserve">
+    <value>The hosts file cannot be saved because it is read-only.</value>
+    <comment>"Hosts" refers to the system hosts file, do not loc</comment>
+  </data>
   <data name="FilterBtn.[using:Microsoft.UI.Xaml.Automation]AutomationProperties.Name" xml:space="preserve">
     <value>Filters</value>
   </data>
@@ -246,6 +250,9 @@
     <value>Hosts</value>
     <comment>"Hosts" refers to the system hosts file, do not loc</comment>
   </data>
+  <data name="MakeWritable.Content" xml:space="preserve">
+    <value>Make writable</value>
+  </data>
   <data name="MoveDown.Text" xml:space="preserve">
     <value>Move down</value>
   </data>

src/modules/Hosts/Hosts/ViewModels/MainViewModel.cs

@@ -15,6 +15,7 @@ using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using CommunityToolkit.WinUI;
 using CommunityToolkit.WinUI.Collections;
+using Hosts.Exceptions;
 using Hosts.Helpers;
 using Hosts.Models;
 using Hosts.Settings;
@@ -48,6 +49,9 @@ namespace Hosts.ViewModels
         [ObservableProperty]
         private string _errorMessage;
 
+        [ObservableProperty]
+        private bool _isReadOnly;
+
         [ObservableProperty]
         private bool _fileChanged;
 
@@ -262,6 +266,13 @@ namespace Hosts.ViewModels
             _hostsService.OpenHostsFile();
         }
 
+        [RelayCommand]
+        public void OverwriteHosts()
+        {
+            _hostsService.RemoveReadOnly();
+            _ = Task.Run(SaveAsync);
+        }
+
         public void Dispose()
         {
             Dispose(disposing: true);
@@ -374,6 +385,7 @@ namespace Hosts.ViewModels
         {
             bool error = true;
             string errorMessage = string.Empty;
+            bool isReadOnly = false;
 
             try
             {
@@ -385,6 +397,12 @@ namespace Hosts.ViewModels
                 var resourceLoader = ResourceLoaderInstance.ResourceLoader;
                 errorMessage = resourceLoader.GetString("FileSaveError_NotElevated");
             }
+            catch (ReadOnlyHostsException)
+            {
+                isReadOnly = true;
+                var resourceLoader = ResourceLoaderInstance.ResourceLoader;
+                errorMessage = resourceLoader.GetString("FileSaveError_ReadOnly");
+            }
             catch (IOException ex) when ((ex.HResult & 0x0000FFFF) == 32)
             {
                 // There are some edge cases where a big hosts file is being locked by svchost.exe https://github.com/microsoft/PowerToys/issues/28066
@@ -402,6 +420,7 @@ namespace Hosts.ViewModels
             {
                 Error = error;
                 ErrorMessage = errorMessage;
+                IsReadOnly = isReadOnly;
             });
         }