[Hosts]Improved save error handling (#28215)

.github/actions/spell-check/expect.txt

@@ -1849,6 +1849,7 @@ subquery
 subresource
 Superbar
 sut
+svchost
 SVE
 SVGIn
 SVGIO

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

@@ -238,5 +238,17 @@ namespace Hosts.Tests
             var result = fileSystem.GetFile(service.HostsFilePath);
             Assert.AreEqual(result.TextContents, contentResult);
         }
+
+        [TestMethod]
+        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);
+            await Assert.ThrowsExceptionAsync<NotRunningElevatedException>(async () => await service.WriteAsync("# Empty hosts file", Enumerable.Empty<Entry>()));
+        }
     }
 }

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

@@ -122,11 +122,11 @@ namespace Hosts.Helpers
             return new HostsData(entries, unparsedBuilder.ToString(), splittedEntries);
         }
 
-        public async Task<bool> WriteAsync(string additionalLines, IEnumerable<Entry> entries)
+        public async Task WriteAsync(string additionalLines, IEnumerable<Entry> entries)
         {
             if (!_elevationHelper.IsElevated)
             {
-                return false;
+                throw new NotRunningElevatedException();
             }
 
             var lines = new List<string>();
@@ -195,18 +195,11 @@ namespace Hosts.Helpers
 
                 await _fileSystem.File.WriteAllLinesAsync(HostsFilePath, lines, Encoding);
             }
-            catch (Exception ex)
-            {
-                Logger.LogError("Failed to write hosts file", ex);
-                return false;
-            }
             finally
             {
                 _fileSystemWatcher.EnableRaisingEvents = true;
                 _asyncLock.Release();
             }
-
-            return true;
         }
 
         public async Task<bool> PingAsync(string address)

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

@@ -17,7 +17,7 @@ namespace Hosts.Helpers
 
         Task<HostsData> ReadAsync();
 
-        Task<bool> WriteAsync(string additionalLines, IEnumerable<Entry> entries);
+        Task WriteAsync(string additionalLines, IEnumerable<Entry> entries);
 
         Task<bool> PingAsync(string address);
 

src/modules/Hosts/Hosts/Helpers/NotRunningElevatedException.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.Helpers
+{
+    public class NotRunningElevatedException : Exception
+    {
+    }
+}

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

@@ -390,6 +390,7 @@
                     x:Uid="FileSaveError"
                     Margin="0,8,0,0"
                     Severity="Error"
+                    Message="{x:Bind ViewModel.ErrorMessage, Mode=TwoWay}"
                     IsOpen="{x:Bind ViewModel.Error, Mode=TwoWay}"
                     Visibility="{x:Bind ViewModel.Error, Mode=TwoWay, Converter={StaticResource BoolToVisibilityConverter}}" />
 

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

@@ -216,8 +216,16 @@
     <value>Hosts file was modified externally.</value>
     <comment>"Hosts" refers to the system hosts file, do not loc</comment>
   </data>
-  <data name="FileSaveError.Message" xml:space="preserve">
+  <data name="FileSaveError_FileInUse" xml:space="preserve">
-    <value>Failed to save hosts file.</value>
+    <value>The hosts file cannot be saved because it is being used by another process.</value>
+    <comment>"Hosts" refers to the system hosts file, do not loc</comment>
+  </data>
+  <data name="FileSaveError_Generic" xml:space="preserve">
+    <value>Unable to save the hosts file.</value>
+    <comment>"Hosts" refers to the system hosts file, do not loc</comment>
+  </data>
+  <data name="FileSaveError_NotElevated" xml:space="preserve">
+    <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="FilterBtn.[using:Microsoft.UI.Xaml.Automation]AutomationProperties.Name" xml:space="preserve">

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

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.IO;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Threading;
@@ -44,6 +45,9 @@ namespace Hosts.ViewModels
         [ObservableProperty]
         private bool _error;
 
+        [ObservableProperty]
+        private string _errorMessage;
+
         [ObservableProperty]
         private bool _fileChanged;
 
@@ -126,12 +130,7 @@ namespace Hosts.ViewModels
         public void UpdateAdditionalLines(string lines)
         {
             AdditionalLines = lines;
-
+            _ = Task.Run(SaveAsync);
-            Task.Run(async () =>
-            {
-                var error = !await _hostsService.WriteAsync(AdditionalLines, _entries);
-                await _dispatcherQueue.EnqueueAsync(() => Error = error);
-            });
         }
 
         public void Move(int oldIndex, int newIndex)
@@ -287,20 +286,12 @@ namespace Hosts.ViewModels
                 return;
             }
 
-            Task.Run(async () =>
+            _ = Task.Run(SaveAsync);
-            {
-                var error = !await _hostsService.WriteAsync(AdditionalLines, _entries);
-                await _dispatcherQueue.EnqueueAsync(() => Error = error);
-            });
         }
 
         private void Entries_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
         {
-            Task.Run(async () =>
+            _ = Task.Run(SaveAsync);
-            {
-                var error = !await _hostsService.WriteAsync(AdditionalLines, _entries);
-                await _dispatcherQueue.EnqueueAsync(() => Error = error);
-            });
         }
 
         private void FindDuplicates(CancellationToken cancellationToken)
@@ -379,6 +370,41 @@ namespace Hosts.ViewModels
             });
         }
 
+        private async Task SaveAsync()
+        {
+            bool error = true;
+            string errorMessage = string.Empty;
+
+            try
+            {
+                await _hostsService.WriteAsync(AdditionalLines, _entries);
+                error = false;
+            }
+            catch (NotRunningElevatedException)
+            {
+                var resourceLoader = ResourceLoaderInstance.ResourceLoader;
+                errorMessage = resourceLoader.GetString("FileSaveError_NotElevated");
+            }
+            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
+                var resourceLoader = ResourceLoaderInstance.ResourceLoader;
+                errorMessage = resourceLoader.GetString("FileSaveError_FileInUse");
+            }
+            catch (Exception ex)
+            {
+                Logger.LogError("Failed to save hosts file", ex);
+                var resourceLoader = ResourceLoaderInstance.ResourceLoader;
+                errorMessage = resourceLoader.GetString("FileSaveError_Generic");
+            }
+
+            await _dispatcherQueue.EnqueueAsync(() =>
+            {
+                Error = error;
+                ErrorMessage = errorMessage;
+            });
+        }
+
         protected virtual void Dispose(bool disposing)
         {
             if (!_disposed)