Get the watchdog working

build/Dockerfile

@@ -5,6 +5,7 @@ COPY tgstation-server.sln ./
 
 COPY src/Tgstation.Server.Host.Console/Tgstation.Server.Host.Console.csproj src/Tgstation.Server.Host.Console/
 COPY src/Tgstation.Server.Host.Watchdog/Tgstation.Server.Host.Watchdog.csproj src/Tgstation.Server.Host.Watchdog/
+COPY src/Tgstation.Server.Host.Startup/Tgstation.Server.Host.Startup.csproj src/Tgstation.Server.Host.Startup/
 COPY src/Tgstation.Server.Host/Tgstation.Server.Host.csproj src/Tgstation.Server.Host/
 COPY src/Tgstation.Server.Api/Tgstation.Server.Api.csproj src/Tgstation.Server.Api/
 
@@ -17,8 +18,8 @@ RUN dotnet restore -nowarn:MSB3202,nu1503 -p:RestoreUseSkipNonexistentTargets=fa
 
 COPY . .
 
-WORKDIR /src/src/Tgstation.Server.Host.Console
-RUN dotnet build -c Release -o /app
+WORKDIR /src/src/Tgstation.Server.Host.Startup
+RUN dotnet build -c Release
 
 WORKDIR /src/tests/Tgstation.Server.Api.Tests
 RUN dotnet test -c Release

src/Tgstation.Server.Host.Startup/IServer.cs

@@ -2,7 +2,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 
-namespace Tgstation.Server.Host
+namespace Tgstation.Server.Host.Startup
 {
 	/// <summary>
 	/// Represents the host

src/Tgstation.Server.Host.Startup/IServerFactory.cs

@@ -1,4 +1,4 @@
-namespace Tgstation.Server.Host
+namespace Tgstation.Server.Host.Startup
 {
 	/// <summary>
 	/// For creating <see cref="IServer"/>s

src/Tgstation.Server.Host.Startup/Tgstation.Server.Host.Startup.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
+    <LangVersion>latest</LangVersion>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <WarningsAsErrors />
+    <DocumentationFile>bin\Release\netstandard2.0\Tgstation.Server.Host.Startup..xml</DocumentationFile>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
+    <LangVersion>latest</LangVersion>
+  </PropertyGroup>
+</Project>

src/Tgstation.Server.Host.Watchdog/IActiveAssemblyDeleter.cs

@@ -0,0 +1,16 @@
+using System.Reflection;
+
+namespace Tgstation.Server.Host.Watchdog
+{
+	/// <summary>
+	/// For deleting <see cref="Assembly"/>s used by the program
+	/// </summary>
+	interface IActiveAssemblyDeleter
+	{
+		/// <summary>
+		/// Deletes an <paramref name="assembly"/> that is in use by the runtime
+		/// </summary>
+		/// <param name="assembly">The <see cref="Assembly"/> to delete</param>
+		void DeleteActiveAssembly(Assembly assembly);
+	}
+}

src/Tgstation.Server.Host.Watchdog/IsolatedServerFactory.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.Loader;
+using Tgstation.Server.Host.Startup;
+
+namespace Tgstation.Server.Host.Watchdog
+{
+	/// <summary>
+	/// <see cref="IServerFactory"/> for loading <see cref="IServer"/>s in a different <see cref="AssemblyLoadContext"/>
+	/// </summary>
+	sealed class IsolatedServerFactory : AssemblyLoadContext, IServerFactory
+	{
+		/// <summary>
+		/// The path of the <see cref="Assembly"/> to load
+		/// </summary>
+		readonly string assemblyPath;
+
+		/// <summary>
+		/// Construct a <see cref="IsolatedServerFactory"/>
+		/// </summary>
+		/// <param name="assemblyPath">The value of <see cref="assemblyPath"/></param>
+		public IsolatedServerFactory(string assemblyPath) => this.assemblyPath = assemblyPath ?? throw new ArgumentNullException(nameof(assemblyPath));
+
+		/// <summary>
+		/// Loads the <see cref="Assembly"/> at <see cref="assemblyPath"/> and creates an <see cref="IServer"/> from it
+		/// </summary>
+		/// <returns>A new <see cref="IServer"/></returns>
+		public IServer CreateServer()
+		{
+			var assembly = LoadFromAssemblyPath(assemblyPath);
+			//find the IServerFactory implementation
+
+			var serverFactoryInterfaceType = typeof(IServerFactory);
+			var serverFactoryImplementationType = assembly.GetTypes().Where(x => serverFactoryInterfaceType.IsAssignableFrom(x)).First();
+
+			var serverFactory = (IServerFactory)Activator.CreateInstance(serverFactoryImplementationType);
+			return serverFactory.CreateServer();
+		}
+
+		//honestly have no idea what this is for, but the examples i see just return null and it seems to work just fine
+		/// <inheritdoc />
+		protected override Assembly Load(AssemblyName assemblyName) => null;
+	}
+}

src/Tgstation.Server.Host.Watchdog/NativeMethods.cs

@@ -0,0 +1,21 @@
+using System.Runtime.InteropServices;
+
+namespace Tgstation.Server.Host.Watchdog
+{
+	static class NativeMethods
+	{
+		public enum MoveFileFlags
+		{
+			None = 0,
+			ReplaceExisting = 1,
+			CopyAllowed = 2,
+			DelayUntilReboot = 4,
+			WriteThrough = 8,
+			CreateHardlink = 16,
+			FailIfNotTrackable = 32,
+		}
+
+		[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
+		public static extern bool MoveFileEx(string lpExistingFileName,	string lpNewFileName, MoveFileFlags dwFlags);
+	}
+}

src/Tgstation.Server.Host.Watchdog/PosixActiveAssemblyDeleter.cs

@@ -0,0 +1,15 @@
+using System;
+using System.IO;
+using System.Reflection;
+
+namespace Tgstation.Server.Host.Watchdog
+{
+	/// <summary>
+	/// See <see cref="IActiveAssemblyDeleter"/> for POSIX systems
+	/// </summary>
+	sealed class PosixActiveAssemblyDeleter : IActiveAssemblyDeleter
+	{
+		/// <inheritdoc />
+		public void DeleteActiveAssembly(Assembly assembly) => File.Delete(assembly?.Location ?? throw new ArgumentNullException(nameof(assembly))); //glory of inodes
+	}
+}

src/Tgstation.Server.Host.Watchdog/Tgstation.Server.Host.Watchdog.csproj

@@ -18,6 +18,12 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.6.0" />
     <PackageReference Include="Octokit" Version="0.29.0" />
+    <PackageReference Include="System.Runtime.Loader" Version="4.3.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Tgstation.Server.Host.Startup\Tgstation.Server.Host.Startup.csproj" />
+    <ProjectReference Include="..\Tgstation.Server.Host\Tgstation.Server.Host.csproj" />
   </ItemGroup>
 
 </Project>

src/Tgstation.Server.Host.Watchdog/Watchdog.cs

@@ -1,58 +1,59 @@
 using System;
 using System.IO;
-using System.Linq;
-using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
+using Tgstation.Server.Host.Startup;
 
 namespace Tgstation.Server.Host.Watchdog
 {
 	/// <inheritdoc />
-	sealed class Watchdog : MarshalByRefObject, IWatchdog
+	sealed class Watchdog : IWatchdog
 	{
-        string DomainName => GetType().Namespace.Replace(nameof(Watchdog), String.Empty);
+		/// <summary>
+		/// The initial <see cref="IServerFactory"/> for the <see cref="Watchdog"/>
+		/// </summary>
+		readonly IServerFactory initialServerFactory;
 
-        string DllName => String.Concat(DomainName, ".dll");
+		/// <summary>
+		/// The <see cref="IActiveAssemblyDeleter"/> for the <see cref="Watchdog"/>
+		/// </summary>
+		readonly IActiveAssemblyDeleter activeAssemblyDeleter;
 
-        async Task<string> RunServer(string[] args, CancellationToken cancellationToken)
-        {
-            var assembly = Assembly.LoadFrom(DllName);
-            //the only thing we need to reflect is the IServerFactory, we can cross reference everything else from there
-            var factoryInterfaceType = assembly.GetType(String.Concat(DomainName, ".IServerFactory"));
-            var factoryType = assembly.GetTypes().Where(x => factoryInterfaceType.IsAssignableFrom(x)).First();
-            var factory = Activator.CreateInstance(factoryType);
-            var factoryFunction = factoryInterfaceType.GetMethods().First();
-            var serverType = factoryFunction.ReturnType;
-            var serverRunFunction = serverType.GetMethods().First();
-            var serverUpdatePathAccessor = serverType.GetProperties().First().GetAccessors().First();
-
-            var server = (IDisposable)factoryFunction.Invoke(factory, Array.Empty<object>());
-            using (server)
-            {
-                var task = (Task)serverRunFunction.Invoke(server, new object[] { args, cancellationToken });
-                await task.ConfigureAwait(false);
-                return (string)serverUpdatePathAccessor.Invoke(server, Array.Empty<object>());
-            }
-        }
+		/// <summary>
+		/// Construct a <see cref="Watchdog"/>
+		/// </summary>
+		/// <param name="initialServerFactory">The value of <see cref="initialServerFactory"/></param>
+		/// <param name="activeAssemblyDeleter">The value of <see cref="activeAssemblyDeleter"/></param>
+		public Watchdog(IServerFactory initialServerFactory, IActiveAssemblyDeleter activeAssemblyDeleter)
+		{
+			this.initialServerFactory = initialServerFactory ?? throw new ArgumentNullException(nameof(initialServerFactory));
+			this.activeAssemblyDeleter = activeAssemblyDeleter ?? throw new ArgumentNullException(nameof(activeAssemblyDeleter));
+		}
 
 		/// <inheritdoc />
 		public async Task RunAsync(string[] args, CancellationToken cancellationToken)
 		{
-			while (!cancellationToken.IsCancellationRequested)
-            {
-                string updatePath = null;
+			//first run the host we started with
+			var serverFactory = initialServerFactory;
+			var assembly = serverFactory.GetType().Assembly;
+			do
+			{
+				string updatePath;
+				using (var server = serverFactory.CreateServer())
+				{
+					serverFactory = null;
+					await server.RunAsync(args, cancellationToken).ConfigureAwait(false);
+					updatePath = server.UpdatePath;
+				}
 
-                await Task.CompletedTask.ConfigureAwait(false);
-
-                if (updatePath == null)
-                    break;
-                
-                //Ensure the assembly is unloaded
-                GC.Collect(Int32.MaxValue, GCCollectionMode.Default, true);
-
-                File.Delete(DllName);
-                File.Move(updatePath, DllName);
-            }
+				if (updatePath == null)
+					break;
+				
+				activeAssemblyDeleter.DeleteActiveAssembly(assembly);
+				File.Move(updatePath, assembly.Location);
+				serverFactory = new IsolatedServerFactory(assembly.Location);
+			}
+			while (!cancellationToken.IsCancellationRequested);
 		}
 	}
 }

src/Tgstation.Server.Host.Watchdog/WatchdogFactory.cs

@@ -1,9 +1,11 @@
-namespace Tgstation.Server.Host.Watchdog
+using System.Runtime.InteropServices;
+
+namespace Tgstation.Server.Host.Watchdog
 {
     /// <inheritdoc />
     public sealed class WatchdogFactory : IWatchdogFactory
     {
         /// <inheritdoc />
-        public IWatchdog CreateWatchdog() => new Watchdog();
+        public IWatchdog CreateWatchdog() => new Watchdog(new ServerFactory(), RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? (IActiveAssemblyDeleter)new WindowsActiveAssemblyDeleter() : new PosixActiveAssemblyDeleter());
     }
 }

src/Tgstation.Server.Host.Watchdog/WindowsActiveAssemblyDeleter.cs

@@ -0,0 +1,32 @@
+using System;
+using System.ComponentModel;
+using System.IO;
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+namespace Tgstation.Server.Host.Watchdog
+{
+	/// <summary>
+	/// See <see cref="IActiveAssemblyDeleter"/> for Windows systems
+	/// </summary>
+	sealed class WindowsActiveAssemblyDeleter : IActiveAssemblyDeleter
+	{
+		/// <inheritdoc />
+		public void DeleteActiveAssembly(Assembly assembly)
+		{
+			if (assembly == null)
+				throw new ArgumentNullException(nameof(assembly));
+			
+			var location = assembly.Location;
+			//Can't use Path.GetTempFileName() because it may cross drives, which won't actually rename the file
+			//Also append the long path prefix just in case we're running on .NET framework
+			var tmpLocation = String.Concat(@"\\?\", assembly.Location, Guid.NewGuid());
+			File.Delete(tmpLocation);
+			File.Move(location, tmpLocation);
+
+			//this deletes the file at reboot, sadly it also triggers a restart notification on server os's but oh well
+			if (!NativeMethods.MoveFileEx(tmpLocation, null, NativeMethods.MoveFileFlags.DelayUntilReboot))
+				throw new Win32Exception(Marshal.GetLastWin32Error());
+		}
+	}
+}

src/Tgstation.Server.Host/Server.cs

@@ -1,5 +1,6 @@
 using System.Threading;
 using System.Threading.Tasks;
+using Tgstation.Server.Host.Startup;
 
 namespace Tgstation.Server.Host
 {
@@ -7,7 +8,7 @@ namespace Tgstation.Server.Host
 	sealed class Server : IServer
     {
         /// <inheritdoc />
-        public string UpdatePath => null;
+        public string UpdatePath => "Tgstation.Server.Host.New.dll";
 
         /// <inheritdoc />
         public void Dispose() { }

src/Tgstation.Server.Host/ServerFactory.cs

@@ -1,4 +1,6 @@
-namespace Tgstation.Server.Host
+using Tgstation.Server.Host.Startup;
+
+namespace Tgstation.Server.Host
 {
 	/// <inheritdoc />
 	public sealed class ServerFactory : IServerFactory

src/Tgstation.Server.Host/Tgstation.Server.Host.csproj

@@ -22,6 +22,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\Tgstation.Server.Api\Tgstation.Server.Api.csproj" />
+    <ProjectReference Include="..\Tgstation.Server.Host.Startup\Tgstation.Server.Host.Startup.csproj" />
   </ItemGroup>
 
 </Project>

tgstation-server.sln

@@ -53,6 +53,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Tgstation.Server.Host.Watch
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Tgstation.Server.Host.Watchdog.Tests", "tests\Tgstation.Server.Host.Watchdog.Tests\Tgstation.Server.Host.Watchdog.Tests.csproj", "{7500F776-4384-4B5F-A8D8-22461CAD108B}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Tgstation.Server.Host.Startup", "src\Tgstation.Server.Host.Startup\Tgstation.Server.Host.Startup.csproj", "{7D067E1B-06A1-49C8-A8E6-7ACBA28A5A41}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -123,6 +125,10 @@ Global
 		{7500F776-4384-4B5F-A8D8-22461CAD108B}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{7500F776-4384-4B5F-A8D8-22461CAD108B}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{7500F776-4384-4B5F-A8D8-22461CAD108B}.Release|Any CPU.Build.0 = Release|Any CPU
+		{7D067E1B-06A1-49C8-A8E6-7ACBA28A5A41}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7D067E1B-06A1-49C8-A8E6-7ACBA28A5A41}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7D067E1B-06A1-49C8-A8E6-7ACBA28A5A41}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7D067E1B-06A1-49C8-A8E6-7ACBA28A5A41}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE