Fix auto-discovery of configuration assemblies in bundled mode

By reading the deps json directly from the application host the with the help of the`Microsoft.NET.HostModel` package.

Author: 0xced

README.md

@@ -115,21 +115,6 @@ For legacy .NET Framework projects it also scans default probing path(s).
 
 For all other cases, as well as in the case of non-conventional configuration assembly names **DO** use [Using](#using-section-and-auto-discovery-of-configuration-assemblies) section.
 
-#### .NET Single File Applications
-
-Currently, auto-discovery of configuration assemblies requires special care when the application is deployed in [bundled mode](https://docs.microsoft.com/en-us/dotnet/core/deploying/single-file/overview).
-
-Starting with version 3.4.0, the configuration assemblies must be explicitly loaded prior to calling `loggerConfiguration.ReadFrom.Configuration(…)`.
-
-```csharp
-// Force loading of assemblies that might be used in the configuration (required when published as single file)
-_ = typeof(ConsoleLoggerConfigurationExtensions).Assembly;
-_ = typeof(SeqLoggerConfigurationExtensions).Assembly;
-loggerConfiguration.ReadFrom.Configuration(context.Configuration);
-```
-
-For versions older than 3.4.0, the [Using](#using-section-and-auto-discovery-of-configuration-assemblies) section must be used to load configuration assemblies as a workaround.
-
 ### MinimumLevel, LevelSwitches, overrides and dynamic reload
 
 The `MinimumLevel` configuration property can be set to a single value as in the sample above, or, levels can be overridden per logging source.

src/Serilog.Settings.Configuration/Serilog.Settings.Configuration.csproj

@@ -41,5 +41,6 @@
 
   <ItemGroup Condition="('$(TargetFramework)' == 'netstandard2.0') Or ('$(TargetFramework)' == 'net461')">
     <PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" Version="2.0.0" />
+    <PackageReference Include="Microsoft.NET.HostModel" Version="3.1.16" />
   </ItemGroup>
 </Project>

src/Serilog.Settings.Configuration/Settings/Configuration/Assemblies/AppDomainAssemblyFinder.cs

@@ -3,6 +3,14 @@
 using System.Reflection;
 using Microsoft.Extensions.DependencyModel;
 
+#if !NET451
+using System.Diagnostics;
+using System.IO;
+using System.IO.MemoryMappedFiles;
+using System.Text;
+using Microsoft.NET.HostModel.AppHost;
+#endif
+
 namespace Serilog.Settings.Configuration.Assemblies
 {
     abstract class AssemblyFinder
@@ -16,20 +24,8 @@ protected static bool IsCaseInsensitiveMatch(string text, string textToFind)
 
         public static AssemblyFinder Auto()
         {
-            try
-            {
-                // Need to check `Assembly.GetEntryAssembly()` first because 
-                // `DependencyContext.Default` throws an exception when `Assembly.GetEntryAssembly()` returns null
-                if (Assembly.GetEntryAssembly() != null && DependencyContext.Default != null)
-                {
-                    return new CompositeAssemblyFinder(new AppDomainAssemblyFinder(), new DependencyContextAssemblyFinder(DependencyContext.Default));
-                }
-            }
-            catch (NotSupportedException) when (typeof(object).Assembly.Location is "") // bundled mode detection
-            {
-            }
-            
-            return new DllScanningAssemblyFinder();
+            var dependencyContext = GetDependencyContext();
+            return dependencyContext != null ? new DependencyContextAssemblyFinder(dependencyContext) : new DllScanningAssemblyFinder();
         }
 
         public static AssemblyFinder ForSource(ConfigurationAssemblySource configurationAssemblySource)
@@ -46,5 +42,48 @@ public static AssemblyFinder ForDependencyContext(DependencyContext dependencyCo
         {
             return new DependencyContextAssemblyFinder(dependencyContext);
         }
+
+        static DependencyContext GetDependencyContext()
+        {
+            var isBundled = string.IsNullOrEmpty(Assembly.GetEntryAssembly()?.Location);
+            if (!isBundled)
+            {
+                return DependencyContext.Default;
+            }
+
+#if !NET451
+            try
+            {
+                var currentProcessPath = Process.GetCurrentProcess().MainModule?.FileName;
+                if (currentProcessPath != null && HostWriter.IsBundle(currentProcessPath, out var bundleHeaderOffset))
+                {
+                    using var mappedFile = MemoryMappedFile.CreateFromFile(currentProcessPath, FileMode.Open);
+                    using var currentProcessStream = mappedFile.CreateViewStream(0, new FileInfo(currentProcessPath).Length, MemoryMappedFileAccess.Read);
+                    using var reader = new BinaryReader(currentProcessStream, Encoding.UTF8);
+                    // See https://github.com/dotnet/runtime/blob/v6.0.3/src/installer/managed/Microsoft.NET.HostModel/Bundle/Manifest.cs#L32-L39
+                    // and https://github.com/dotnet/runtime/blob/v6.0.3/src/installer/managed/Microsoft.NET.HostModel/Bundle/Manifest.cs#L144-L155
+                    reader.BaseStream.Position = bundleHeaderOffset;
+                    var majorVersion = reader.ReadUInt32();
+                    _ = reader.ReadUInt32(); // minorVersion
+                    _ = reader.ReadInt32(); // numEmbeddedFiles
+                    _ = reader.ReadString(); // bundleId
+                    if (majorVersion >= 2)
+                    {
+                        var depsJsonOffset = reader.ReadInt64();
+                        var depsJsonSize = reader.ReadInt64();
+                        using var depsJsonStream = mappedFile.CreateViewStream(depsJsonOffset, depsJsonSize, MemoryMappedFileAccess.Read);
+                        using var depsJsonReader = new DependencyContextJsonReader();
+                        return depsJsonReader.Read(depsJsonStream);
+                    }
+                }
+            }
+            catch
+            {
+                return null;
+            }
+#endif
+
+            return null;
+        }
     }
 }

src/Serilog.Settings.Configuration/Settings/Configuration/Assemblies/AssemblyFinder.cs

@@ -6,13 +6,6 @@
 
 try
 {
-    // Force loading of assemblies could become unnecessary if the [DependencyContextLoader][1]
-    // starts supporting applications published as single-file in the future.
-    // Unfortunately, as of .NET 6, loading the DependencyContext from a single-file application is not supported.
-    // [1]: https://github.com/dotnet/runtime/blob/v6.0.3/src/libraries/Microsoft.Extensions.DependencyModel/src/DependencyContextLoader.cs#L54-L55
-    _ = typeof(Serilog.Sinks.InMemory.InMemorySinkExtensions).Assembly;
-    _ = typeof(ConsoleLoggerConfigurationExtensions).Assembly;
-
     SelfLog.Enable(text => Console.Error.WriteLine(text));
 
     var configuration = new ConfigurationBuilder().AddInMemoryCollection(new Dictionary<string, string>