SIANXSVC-1186: Terminate application after writing metadata (#20)

* SIANXSVC-1186: Update documentation for dotnet-e5e for service initialization
* SIANXSVC-1186: Exit application after writing metadata

Closes SIANXSVC-1186

README.md

@@ -100,6 +100,24 @@ await host.RunAsync();
 
 Further examples can be found in the [examples folder](./examples).
 
+### Note on startup initialization
+
+Due to the fact that the communication with e5e relies on the `IHost` to run, any initialization code should
+**not** be done before starting the host. It **must** be done after starting the host, for example by splitting
+up the `RunAsync` call like in the example below.
+
+```csharp
+using var host = /* ...omitted for brevity */
+
+// Don't do this or bad things are going to happen.
+await SomeExtremelyLongStartupTask();
+
+// Instead do this:
+await host.StartAsync();
+await SomeExtremelyLongStartupTask();
+await host.WaitForShutdownAsync();
+```
+
 # Supported versions
 
 |                        | Supported |

src/Anexia.E5E.Tests/Integration/StartupTests.cs

@@ -2,10 +2,13 @@
 using System.Threading;
 using System.Threading.Tasks;
 
+using Anexia.E5E.Abstractions.Termination;
 using Anexia.E5E.Runtime;
 using Anexia.E5E.Serialization;
 using Anexia.E5E.Tests.TestHelpers;
 
+using Microsoft.Extensions.DependencyInjection;
+
 using Xunit;
 using Xunit.Abstractions;
 
@@ -36,5 +39,7 @@ public async Task TerminatesAutomatically()
 		cts.Token.Register(() => Assert.Fail("Shutdown took longer than three seconds"), true);
 
 		await Host.WaitForShutdownAsync(cts.Token);
+		var terminator = Host.Inner.Services.GetRequiredService<ITerminator>() as TerminatorMock;
+		Assert.True(terminator?.Called);
 	}
 }

src/Anexia.E5E.Tests/TestHelpers/TerminatorMock.cs

@@ -0,0 +1,10 @@
+using Anexia.E5E.Abstractions.Termination;
+
+namespace Anexia.E5E.Tests.TestHelpers;
+
+public class TerminatorMock : ITerminator
+{
+	public void Exit() { Called = true; }
+
+	public bool Called { get; private set; }
+}

src/Anexia.E5E.Tests/TestHelpers/TestHostBuilder.cs

@@ -4,6 +4,7 @@
 using System.Threading.Tasks;
 
 using Anexia.E5E.Abstractions;
+using Anexia.E5E.Abstractions.Termination;
 using Anexia.E5E.Extensions;
 using Anexia.E5E.Functions;
 using Anexia.E5E.Runtime;
@@ -53,7 +54,11 @@ public TestHostBuilder ConfigureEndpoints(Action<IE5EEntrypointBuilder> configur
 	public Task StartAsync(int maximumLifetimeMs = 5000)
 	{
 		// In order to override the default implementation, we need to call this just before we build our host.
-		_hb.ConfigureServices(services => services.AddSingleton<IConsoleAbstraction, TestConsoleAbstraction>());
+		_hb.ConfigureServices(services =>
+		{
+			services.AddSingleton<IConsoleAbstraction, TestConsoleAbstraction>();
+			services.AddSingleton<ITerminator, TerminatorMock>();
+		});
 		_host = _hb.Build();
 
 		// Shutdown the host automatically after five seconds, there's no test that should run that long.

src/Anexia.E5E/Abstractions/Termination/EnvironmentTerminator.cs

@@ -0,0 +1,6 @@
+namespace Anexia.E5E.Abstractions.Termination;
+
+internal sealed class EnvironmentTerminator : ITerminator
+{
+	public void Exit() => Environment.Exit(0);
+}

src/Anexia.E5E/Abstractions/Termination/ITerminator.cs

@@ -0,0 +1,10 @@
+namespace Anexia.E5E.Abstractions.Termination;
+
+/// <summary>
+/// Because the usage of <see cref="Environment.Exit"/> would also crash our test processes, it is abstracted.
+/// By default, the <see cref="EnvironmentTerminator"/> is used as implementation.
+/// </summary>
+internal interface ITerminator
+{
+	void Exit();
+}

src/Anexia.E5E/Anexia.E5E.csproj

@@ -55,4 +55,9 @@
 		<PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.0"/>
 		<PackageReference Include="DotNet.ReproducibleBuilds" Version="1.1.1" PrivateAssets="All"/>
 	</ItemGroup>
+
+	<ItemGroup>
+		<!-- Make the internal members visible to Anexia.E5E.Tests -->
+		<InternalsVisibleTo Include="$(AssemblyName).Tests"/>
+	</ItemGroup>
 </Project>

src/Anexia.E5E/Hosting/E5EHostWrapper.cs

@@ -1,6 +1,7 @@
 using System.Text.Json;
 
 using Anexia.E5E.Abstractions;
+using Anexia.E5E.Abstractions.Termination;
 using Anexia.E5E.Runtime;
 using Anexia.E5E.Serialization;
 
@@ -12,6 +13,7 @@ namespace Anexia.E5E.Hosting;
 internal sealed class E5EHostWrapper : IHost
 {
 	private readonly IConsoleAbstraction _console;
+	private readonly ITerminator _terminator;
 	private readonly IHost _host;
 	private readonly E5ERuntimeOptions _options;
 
@@ -20,6 +22,7 @@ public E5EHostWrapper(IHost host)
 		_host = host;
 		_options = Services.GetRequiredService<E5ERuntimeOptions>();
 		_console = Services.GetRequiredService<IConsoleAbstraction>();
+		_terminator = Services.GetService<ITerminator>() ?? new EnvironmentTerminator();
 	}
 
 	public void Dispose()
@@ -35,21 +38,20 @@ public async Task StartAsync(CancellationToken cancellationToken = default)
 			return;
 		}
 
-		string metadata = "";
 #if NET8_0_OR_GREATER
-		metadata = JsonSerializer.Serialize(new E5ERuntimeMetadata(),
+		var metadata = JsonSerializer.Serialize(new E5ERuntimeMetadata(),
 			E5ESerializationContext.Default.E5ERuntimeMetadata);
 #else
-		metadata = JsonSerializer.Serialize(new E5ERuntimeMetadata(), E5EJsonSerializerOptions.Default);
+		var metadata = JsonSerializer.Serialize(new E5ERuntimeMetadata(), E5EJsonSerializerOptions.Default);
 #endif
 
 		_console.Open();
 		await _console.WriteToStdoutAsync(metadata).ConfigureAwait(false);
 		_console.Close();
 
-		// If we wrote the metadata, circumvent the default host mechanism as used by Run/RunAsync extensions
-		// and just stop the application.
-		_host.Services.GetRequiredService<IHostApplicationLifetime>().StopApplication();
+		// After we wrote the metadata, close the application immediately(!). Any startup tasks that occur after the startup
+		// (e.g. a long initialization task) won't be executed and the metadata is returned to e5e.
+		_terminator.Exit();
 	}
 
 	public Task StopAsync(CancellationToken cancellationToken = default)