Update settings file atomically to prevent locking issues; avoid crashing if file is empty/corrupt

Author: maxkagamine

AutoAudioSwitcher/Program.cs

@@ -12,6 +12,7 @@
 using System.Diagnostics;
 using System.Reactive;
 using System.Reactive.Linq;
+using System.Text.Json;
 
 namespace AutoAudioSwitcher;
 
@@ -20,6 +21,7 @@ internal sealed class Program
     private static readonly TimeSpan WindowsAutomaticDefaultDeviceChangeThreshold = TimeSpan.FromSeconds(2);
 
     private const string LogsDirectory = "logs";
+    public const string SettingsFile = "appsettings.json";
 
     private static readonly LoggingLevelSwitch levelSwitch = new(LogEventLevel.Error);
     private static ServiceProvider? provider;
@@ -30,13 +32,19 @@ private static ServiceProvider ConfigureServices()
     {
         ServiceCollection services = new();
 
-        if (!File.Exists("appsettings.json"))
+        if (!File.Exists(SettingsFile))
         {
             new Settings().Save();
         }
 
         IConfiguration config = new ConfigurationBuilder()
-            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
+            .AddJsonFile(SettingsFile, optional: false, reloadOnChange: true)
+            .SetFileLoadExceptionHandler(e =>
+            {
+                // Happens if the file is empty or not a JSON object. This will revert the settings to default; no point
+                // showing an error here since IConfiguration normally ignores invalid property values anyway.
+                e.Ignore = e.Exception.GetBaseException() is JsonException;
+            })
             .Build();
 
         services.ConfigureObservable<Settings>(config);

AutoAudioSwitcher/Settings.cs

@@ -27,12 +27,25 @@ internal sealed record Settings : IEquatable<Settings?>
     public LogEventLevel LogLevel { get; init; } = LogEventLevel.Error;
 
     /// <summary>
-    /// Writes the current <see cref="Settings"/> to appsettings.json.
+    /// Writes the current <see cref="Settings"/> to the settings file.
     /// </summary>
     public void Save()
     {
-        using FileStream file = File.Open("appsettings.json", FileMode.Create, FileAccess.Write);
-        JsonSerializer.Serialize(file, this, SettingsSerializerContext.Default.Options);
+        try
+        {
+            string tempFile = $"{Program.SettingsFile}.tmp";
+
+            using (FileStream file = File.Open(tempFile, FileMode.Create, FileAccess.Write))
+            {
+                JsonSerializer.Serialize(file, this, SettingsSerializerContext.Default.Options);
+            }
+
+            File.Move(tempFile, Program.SettingsFile, overwrite: true);
+        }
+        catch (Exception ex)
+        {
+            throw new Exception($"Failed to save settings file \"{Path.GetFullPath(Program.SettingsFile)}\".", ex);
+        }
     }
 
     public bool Equals(Settings? other)