Support ServerHost.Exiting event

src/Directory.Build.props

@@ -29,7 +29,7 @@
 
 		<!-- Make the assembly, file, and NuGet package versions the same. -->
 		<!-- https://docs.microsoft.com/en-us/nuget/concepts/package-versioning#pre-release-versions -->
-		<Version>0.4.0-alpha</Version>
+		<Version>0.5.0-beta</Version>
 	</PropertyGroup>
 
 	<PropertyGroup Condition="'$(Configuration)'=='Debug'">

src/Menees.Remoting/IServerHost.cs

@@ -16,8 +16,10 @@ public interface IServerHost
 	bool IsReady { get; }
 
 	/// <summary>
-	/// Tells the host to begin the shutdown process and to signal any associated <see cref="IServer"/> instances to stop.
+	/// Asks the host to begin the shutdown process and to signal any associated <see cref="IServer"/> instances to stop.
 	/// </summary>
 	/// <param name="exitCode">An optional exit code to pass to the host.</param>
-	void Exit(int? exitCode = null);
+	/// <returns>True if the shutdown process was begun. False if it was cancelled by a server-side event handler
+	/// (e.g., by <see cref="ServerHost.Exiting"/>).</returns>
+	bool Exit(int? exitCode = null);
 }

src/Menees.Remoting/ServerHost.cs

@@ -2,6 +2,7 @@
 
 #region Using Directives
 
+using System.ComponentModel;
 using System.Runtime.CompilerServices;
 
 #endregion
@@ -20,6 +21,15 @@ public sealed class ServerHost : IServerHost, IDisposable
 
 	#endregion
 
+	#region Public Events
+
+	/// <summary>
+	/// Raised when <see cref="IServerHost.Exit(int?)"/> is called to allow logging and/or cancellation.
+	/// </summary>
+	public event CancelEventHandler? Exiting;
+
+	#endregion
+
 	#region Public Properties
 
 	bool IServerHost.IsReady => !this.resetEvent.IsSet;
@@ -35,16 +45,36 @@ public sealed class ServerHost : IServerHost, IDisposable
 
 	/// <inheritdoc/>
 	/// <exception cref="ObjectDisposedException">If <see cref="Dispose()"/> has been called already.</exception>
-	/// <exception cref="InvalidOperationException">If <see cref="IServerHost.Exit"/> has been called already.</exception>
-	void IServerHost.Exit(int? exitCode)
+	/// <exception cref="InvalidOperationException">If <see cref="IServerHost.Exit"/> has started already.</exception>
+	bool IServerHost.Exit(int? exitCode)
 	{
 		this.EnsureReady();
-		this.ExitCode = exitCode;
 
-		// Give the caller a little time to receive our response and disconnect.
-		// Otherwise, this process could end too soon, and the client would get an ArgumentException
-		// like "Unable to read 4 byte message length from stream. Only 0 bytes were available.".
-		this.StartExiting();
+		CancelEventArgs should = new();
+		int? previousExitCode = this.ExitCode;
+		try
+		{
+			this.ExitCode = exitCode;
+			this.Exiting?.Invoke(this, should);
+		}
+		finally
+		{
+			if (should.Cancel)
+			{
+				this.ExitCode = previousExitCode;
+			}
+		}
+
+		bool exit = !should.Cancel;
+		if (exit)
+		{
+			// Give the caller a little time to receive our response and disconnect.
+			// Otherwise, this process could end too soon, and the client would get an ArgumentException
+			// like "Unable to read 4 byte message length from stream. Only 0 bytes were available.".
+			this.StartExiting();
+		}
+
+		return exit;
 	}
 
 	/// <inheritdoc/>
@@ -61,7 +91,7 @@ public void Dispose()
 	/// <param name="server">A server instance.</param>
 	/// <exception cref="ArgumentNullException"><paramref name="server"/> is null.</exception>
 	/// <exception cref="ObjectDisposedException">If <see cref="Dispose()"/> has been called already.</exception>
-	/// <exception cref="InvalidOperationException">If <see cref="IServerHost.Exit"/> has been called already.</exception>
+	/// <exception cref="InvalidOperationException">If <see cref="IServerHost.Exit"/> has started already.</exception>
 	public void Add(IServer server)
 	{
 		if (server == null)
@@ -87,7 +117,7 @@ public void Add(IServer server)
 	}
 
 	/// <summary>
-	/// Waits for all added <see cref="IServer"/> instances to stop after <see cref="IServerHost.Exit"/> is called.
+	/// Waits for all added <see cref="IServer"/> instances to stop after <see cref="IServerHost.Exit"/> is started.
 	/// </summary>
 	public void WaitForExit() => this.resetEvent.Wait();
 
@@ -186,7 +216,7 @@ private void EnsureReady([CallerMemberName] string? callerMemberName = null)
 
 		if (this.isExiting)
 		{
-			throw new InvalidOperationException($"{callerMemberName} can't be called after {nameof(IServerHost.Exit)}.");
+			throw new InvalidOperationException($"{callerMemberName} can't be called after {nameof(IServerHost.Exit)} starts.");
 		}
 	}
 

tests/Menees.Remoting.Tests/BaseTests.cs

@@ -4,6 +4,7 @@
 
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 
@@ -20,6 +21,8 @@ public class BaseTests
 
 	#region Public Properties
 
+	public static bool IsDotNetFramework { get; } = RuntimeInformation.FrameworkDescription.Contains("Framework");
+
 	public ILoggerFactory LoggerFactory => this.logManager?.LoggerFactory ?? NullLoggerFactory.Instance;
 
 	#endregion

tests/Menees.Remoting.Tests/RmiServerTests.cs

@@ -74,13 +74,27 @@ public void InProcessServer()
 		server.ReportUnhandledException = WriteUnhandledServerException;
 		host.Add(server);
 
-		using RmiClient<IServerHost> client = new(serverPath, connectTimeout: TimeSpan.FromSeconds(2), loggerFactory: this.LoggerFactory);
+		// When this test runs by itself a short timeout is ok. When run with other tests that use a lot of
+		// client connections (e.g., MessageNodeTests.StringToCodeNameInProcessAsync), then this client's
+		// proxies on .NET Framework can get a semaphore timeout inside NamedPipeClientStream.Connect.
+		// That doesn't happen with .NET Core. Since we intentionally test for a TimeoutException at the
+		// end, we want this timeout to be as short as we can get away with.
+		TimeSpan connectTimeout = TimeSpan.FromSeconds(IsDotNetFramework ? 10 : 2);
+		using RmiClient<IServerHost> client = new(serverPath, connectTimeout, loggerFactory: this.LoggerFactory);
 		IServerHost proxy = client.CreateProxy();
 		IServerHost direct = host;
 		proxy.IsReady.ShouldBeTrue();
 		direct.IsReady.ShouldBeTrue();
+
+		// Test IServerHost.Exit method and ServerHost.Exiting event.
+		host.ExitCode.ShouldBeNull();
+		bool allowExit = false;
+		host.Exiting += (s, e) => e.Cancel = !allowExit;
+		proxy.Exit(0).ShouldBeFalse();
 		host.ExitCode.ShouldBeNull();
-		proxy.Exit(0);
+		direct.IsReady.ShouldBeTrue();
+		allowExit = true;
+		proxy.Exit(0).ShouldBeTrue();
 		host.ExitCode.ShouldBe(0);
 		host.WaitForExit();