New Middleware demo in C# (#297)

csharp/Ice/Middleware/Client/Client.csproj

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+<?xml version="1.0" encoding="utf-8" ?>
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <!-- Copy the PDBs from the NuGet packages to get file names and line numbers in stack traces. -->
+    <CopyDebugSymbolFilesFromPackages>true</CopyDebugSymbolFilesFromPackages>
+  </PropertyGroup>
+  <ItemGroup>
+    <SliceCompile Include="../slice/Greeter.ice" />
+    <PackageReference Include="zeroc.ice.net" Version="3.8.0-alpha0" />
+    <PackageReference Include="zeroc.icebuilder.msbuild" Version="5.0.9" />
+    <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+</Project>

csharp/Ice/Middleware/Client/Program.cs

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+// Copyright (c) ZeroC, Inc.
+
+// Slice module VisitorCenter in Greeter.ice maps to C# namespace VisitorCenter.
+using VisitorCenter;
+
+// Create an Ice communicator to initialize the Ice runtime.
+using Ice.Communicator communicator = Ice.Util.initialize(ref args);
+
+// Create a Greeter proxy. If you run the server on a different computer, replace localhost in the string below with
+// the server's hostname or IP address.
+GreeterPrx greeter = GreeterPrxHelper.createProxy(communicator, "greeter:tcp -h localhost -p 4061");
+
+// We hardcode the tokens in this demo, for simplicity. A real application would obtain the token from a secure source.
+string validToken = "iced tea";
+
+// Send a request to the remote object with an invalid token in the request context.
+try
+{
+    string unexpected = await greeter.GreetAsync(
+        Environment.UserName,
+        context: new Dictionary<string, string> { ["token"] = "pineapple" });
+
+    Console.WriteLine($"Received unexpected greeting: {unexpected}");
+}
+catch (Ice.ObjectNotExistException)
+{
+    // Expected with an invalid (or missing) token. See AuthorizationMiddleware.
+}
+
+// Send a request with the correct token in the request context.
+string greeting = await greeter.GreetAsync(
+    Environment.UserName,
+    context: new Dictionary<string, string> { ["token"] = validToken });
+
+Console.WriteLine(greeting);

csharp/Ice/Middleware/Middleware.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.4.33122.133
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Client", "Client\Client.csproj", "{BBF1199A-46A4-4AE9-AFFE-4D8DD59EB874}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Server", "Server\Server.csproj", "{527EEA4D-77B9-4252-A2CD-C641A25CAD53}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{FBDAF448-665A-4595-98D3-4538C56A666D}"
+	ProjectSection(SolutionItems) = preProject
+		README.md = README.md
+	EndProjectSection
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{BBF1199A-46A4-4AE9-AFFE-4D8DD59EB874}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{BBF1199A-46A4-4AE9-AFFE-4D8DD59EB874}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{BBF1199A-46A4-4AE9-AFFE-4D8DD59EB874}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{BBF1199A-46A4-4AE9-AFFE-4D8DD59EB874}.Release|Any CPU.Build.0 = Release|Any CPU
+		{527EEA4D-77B9-4252-A2CD-C641A25CAD53}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{527EEA4D-77B9-4252-A2CD-C641A25CAD53}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{527EEA4D-77B9-4252-A2CD-C641A25CAD53}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{527EEA4D-77B9-4252-A2CD-C641A25CAD53}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {0B36F1E1-0592-4A15-9981-67BC4A653EC4}
+	EndGlobalSection
+EndGlobal

csharp/Ice/Middleware/README.md

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+# Middleware
+
+The Middleware demo shows how to write a simple middleware and how to add this middleware to an object adapter.
+
+Each object adapter maintains a dispatch pipeline:
+
+```mermaid
+flowchart LR
+    client[Client] -- request --> am -- response --> client
+    subgraph pipeline [Dispatch pipeline]
+        direction LR
+        am[Authorization <br>middleware] --> om[Other <br>middleware] --> Servant --> om --> am
+    end
+```
+
+> [!NOTE]
+> Other middleware is just an example, and is not provided by this demo.
+
+You can build the client and server applications with:
+
+``` shell
+dotnet build
+```
+
+First start the Server program:
+
+```shell
+cd Server
+dotnet run
+```
+
+In a separate terminal, start the Client program:
+
+```shell
+cd Client
+dotnet run
+```

csharp/Ice/Middleware/Server/AuthorizationMiddleware.cs

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+// Copyright (c) ZeroC, Inc.
+
+namespace Server;
+
+/// <summary>The AuthorizationMiddleware intercepts incoming requests and checks the token entry in their contexts.
+/// </summary>
+internal class AuthorizationMiddleware : Ice.Object
+{
+    private readonly Ice.Object _next;
+    private readonly string _validToken;
+
+    /// <inheritdoc />
+    public ValueTask<Ice.OutgoingResponse> dispatchAsync(Ice.IncomingRequest request)
+    {
+        // Check if the request has a valid token in its context.
+        if (!request.current.ctx.TryGetValue("token", out string? token) || token != _validToken)
+        {
+            Console.WriteLine($"Rejecting request with token '{token}'");
+
+            // ObjectNotExistException is one of the 6 Ice local exceptions that Ice transmits "over the wire".
+            // It usually means "no servant was found for this identity". Here, we reuse it to indicate an authorization
+            // failure without leaking information to the client.
+            throw new Ice.ObjectNotExistException();
+        }
+
+        Console.WriteLine($"Accepting request with token '{token}'");
+
+        // Continue the dispatch pipeline.
+        return _next.dispatchAsync(request);
+    }
+
+    /// <summary>Constructs an AuthorizationMiddleware.</summary>
+    /// <param name="next">The next Ice.Object in the dispatch pipeline.</param>
+    /// <param name="validToken">The value to check against.</param>
+    internal AuthorizationMiddleware(Ice.Object next, string validToken)
+    {
+        _next = next;
+        _validToken = validToken;
+    }
+}

csharp/Ice/Middleware/Server/Chatbot.cs

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+// Copyright (c) ZeroC, Inc.
+
+using VisitorCenter;
+
+namespace Server;
+
+/// <summary>Chatbot is an Ice servant that implements Slice interface Greeter.</summary>
+internal class Chatbot : GreeterDisp_
+{
+    /// <inheritdoc />
+    /// // Implements the abstract method Greet from the GreeterDisp_ class generated by the Slice compiler.
+    public override string Greet(string name, Ice.Current current)
+    {
+        Console.WriteLine($"Dispatching greet request {{ name = '{name}' }}");
+        return $"Hello, {name}!";
+    }
+}

csharp/Ice/Middleware/Server/Program.cs

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+// Copyright (c) ZeroC, Inc.
+
+// Create an Ice communicator to initialize the Ice runtime.
+using Ice.Communicator communicator = Ice.Util.initialize(ref args);
+
+// Create an object adapter that listens for incoming requests and dispatches them to servants.
+Ice.ObjectAdapter adapter = communicator.createObjectAdapterWithEndpoints("GreeterAdapter", "tcp -p 4061");
+
+// Install the Authorization middleware in the object adapter.
+adapter.use(next => new Server.AuthorizationMiddleware(next, validToken: "iced tea"));
+
+// Register the Chatbot servant with the adapter.
+adapter.add(new Server.Chatbot(), Ice.Util.stringToIdentity("greeter"));
+
+// Start dispatching requests.
+adapter.activate();
+Console.WriteLine("Listening on port 4061...");
+
+// Wait until the user presses Ctrl+C.
+await CancelKeyPressed;
+Console.WriteLine("Caught Ctrl+C, exiting...");

csharp/Ice/Middleware/Server/Server.csproj

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+<?xml version="1.0" encoding="utf-8" ?>
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <!-- Copy the PDBs from the NuGet packages to get file names and line numbers in stack traces. -->
+    <CopyDebugSymbolFilesFromPackages>true</CopyDebugSymbolFilesFromPackages>
+  </PropertyGroup>
+  <ItemGroup>
+    <SliceCompile Include="../slice/Greeter.ice" />
+    <PackageReference Include="zeroc.ice.net" Version="3.8.0-alpha0" />
+    <PackageReference Include="zeroc.icebuilder.msbuild" Version="5.0.9" />
+    <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <Compile Include="../../../Common/Program.CancelKeyPressed.cs" Link="Program.CancelKeyPressed.cs" />
+  </ItemGroup>
+</Project>

csharp/Ice/Middleware/slice/Greeter.ice

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+// Copyright (c) ZeroC, Inc.
+
+#pragma once
+
+module VisitorCenter
+{
+    /// Represents a simple greeter.
+    interface Greeter
+    {
+        /// Creates a personalized greeting.
+        /// @param name The name of the person to greet.
+        /// @return The greeting.
+        ["cs:identifier:Greet"] // We prefer PascalCase for C# methods.
+        string greet(string name);
+    }
+}