Add emulator handler for SetBackendService

docs/EmulatorPolicyChecklist.md

@@ -61,7 +61,7 @@ Track progress of emulator policy handler implementation. Each policy needs a ha
 | ⬜ | RateLimitByKey | RateLimitByKeyHandler.cs | No-op + callbacks | `emulator/rate-limit-by-key` |
 | ✅ | RewriteUri | RewriteUriHandler.cs | Context mutation | `emulator/rewrite-uri` |
 | ⬜ | SendRequest | SendRequestHandler.cs | External service mock | `emulator/send-request` |
-| ⬜ | SetBackendService | SetBackendServiceHandler.cs | Context mutation | `emulator/set-backend-service` |
+| ✅ | SetBackendService | SetBackendServiceHandler.cs | Context mutation | `emulator/set-backend-service` |
 | ⬜ | ValidateJwt | ValidateJwtHandler.cs | Validation + short-circuit | `emulator/validate-jwt` |
 
 ## Existing Handlers Missing Tests Only

src/Testing/Document/TestDocumentExtensions.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation.
+// Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
 using Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring;
@@ -32,6 +32,9 @@ public static ResponseExampleStore SetupResponseExampleStore(this TestDocument d
     public static LoggerStore SetupLoggerStore(this TestDocument document) =>
         document.Context.LoggerStore;
 
+    public static BackendStore SetupBackendStore(this TestDocument document) =>
+        document.Context.BackendStore;
+
     public static RateLimitStore SetupRateLimitStore(this TestDocument document) =>
         document.Context.RateLimitStore;
 }

src/Testing/Emulator/BadRuntimeConfigurationException.cs

@@ -0,0 +1,9 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Testing.Emulator;
+
+public class BadRuntimeConfigurationException(string message) : Exception(message)
+{
+    public required string Policy { get; init; }
+}

src/Testing/Emulator/Data/Backend.cs

@@ -0,0 +1,6 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Testing.Emulator.Data;
+
+public record Backend(string Id, string Url);

src/Testing/Emulator/Data/BackendStore.cs

@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System.Diagnostics.CodeAnalysis;
+
+namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Testing.Emulator.Data;
+
+public class BackendStore
+{
+    private readonly Dictionary<string, Backend> _backends = new();
+
+    public BackendStore Add(string id, string url)
+    {
+        var backend = new Backend(id, url);
+        Add(backend);
+        return this;
+    }
+
+    public void Add(Backend backend)
+    {
+        if (!_backends.TryAdd(backend.Id, backend))
+        {
+            throw new Exception($"Backend with id '{backend.Id}' already exists.");
+        }
+    }
+
+    public bool TryGet(string id, [NotNullWhen(true)] out Backend? backend) =>
+        _backends.TryGetValue(id, out backend);
+}

src/Testing/Emulator/Policies/SetBackendServiceHandler.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 using Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring;
+using Microsoft.Azure.ApiManagement.PolicyToolkit.Testing.Expressions;
 
 namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Testing.Emulator.Policies;
 
@@ -17,6 +18,34 @@ internal class SetBackendServiceHandler : PolicyHandler<SetBackendServiceConfig>
 
     protected override void Handle(GatewayContext context, SetBackendServiceConfig config)
     {
-        throw new NotImplementedException();
+        if (config.BaseUrl is not null)
+        {
+            SetServiceUrl(context, config.BaseUrl);
+        }
+        else if (config.BackendId is not null)
+        {
+            if (!context.BackendStore.TryGet(config.BackendId, out var backend))
+            {
+                throw new BadRuntimeConfigurationException(
+                    $"Backend with id '{config.BackendId}' could not be found.")
+                {
+                    Policy = PolicyName
+                };
+            }
+
+            SetServiceUrl(context, backend.Url);
+        }
+    }
+
+    private static void SetServiceUrl(GatewayContext context, string url)
+    {
+        var uri = new Uri(url);
+        context.Api.ServiceUrl = new MockUrl
+        {
+            Scheme = uri.Scheme,
+            Host = uri.Host,
+            Port = uri.Port.ToString(),
+            Path = uri.AbsolutePath
+        };
     }
 }

src/Testing/Emulator/SectionContextProxy.cs

@@ -46,6 +46,7 @@ public static SectionContextProxy<TSection> Create(GatewayContext expressionCont
         }
         catch (FinishSectionProcessingException) { throw; }
         catch (PolicyException) { throw; }
+        catch (BadRuntimeConfigurationException) { throw; }
         catch (Exception e)
         {
             throw new PolicyException(e) { Policy = targetMethod.Name, Section = _sectionName, PolicyArgs = args };

src/Testing/GatewayContext.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation.
+// Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
 using Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring;
@@ -18,6 +18,7 @@ public class GatewayContext : MockExpressionContext
     internal readonly CacheStore CacheStore = new();
     internal readonly ResponseExampleStore ResponseExampleStore = new();
     internal readonly LoggerStore LoggerStore = new();
+    internal readonly BackendStore BackendStore = new();
     internal readonly RateLimitStore RateLimitStore = new();
 
     public GatewayContext()

test/Test.Testing/Emulator/Policies/SetBackendServiceTests.cs

@@ -0,0 +1,141 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring;
+using Microsoft.Azure.ApiManagement.PolicyToolkit.Testing;
+using Microsoft.Azure.ApiManagement.PolicyToolkit.Testing.Document;
+using Microsoft.Azure.ApiManagement.PolicyToolkit.Testing.Emulator;
+
+namespace Test.Emulator.Emulator.Policies;
+
+[TestClass]
+public class SetBackendServiceTests
+{
+    class SetBackendServiceWithBaseUrl : IDocument
+    {
+        public void Inbound(IInboundContext context)
+        {
+            context.SetBackendService(new SetBackendServiceConfig
+            {
+                BaseUrl = "https://new-backend.example.com/api"
+            });
+        }
+
+        public void Backend(IBackendContext context)
+        {
+            context.SetBackendService(new SetBackendServiceConfig
+            {
+                BaseUrl = "https://backend-section.example.com"
+            });
+        }
+
+        public void Outbound(IOutboundContext context)
+        {
+            context.SetBackendService(new SetBackendServiceConfig
+            {
+                BaseUrl = "https://outbound-backend.example.com"
+            });
+        }
+
+        public void OnError(IOnErrorContext context)
+        {
+            context.SetBackendService(new SetBackendServiceConfig
+            {
+                BaseUrl = "https://error-backend.example.com"
+            });
+        }
+    }
+
+    class SetBackendServiceWithBackendId : IDocument
+    {
+        public void Inbound(IInboundContext context)
+        {
+            context.SetBackendService(new SetBackendServiceConfig
+            {
+                BackendId = "my-backend"
+            });
+        }
+    }
+
+    [TestMethod]
+    public void SetBackendService_BaseUrl_Inbound()
+    {
+        var test = new SetBackendServiceWithBaseUrl().AsTestDocument();
+
+        test.RunInbound();
+
+        test.Context.Api.ServiceUrl.Scheme.Should().Be("https");
+        test.Context.Api.ServiceUrl.Host.Should().Be("new-backend.example.com");
+        test.Context.Api.ServiceUrl.Path.Should().Be("/api");
+    }
+
+    [TestMethod]
+    public void SetBackendService_BaseUrl_Backend()
+    {
+        var test = new SetBackendServiceWithBaseUrl().AsTestDocument();
+
+        test.RunBackend();
+
+        test.Context.Api.ServiceUrl.Host.Should().Be("backend-section.example.com");
+    }
+
+    [TestMethod]
+    public void SetBackendService_BaseUrl_Outbound()
+    {
+        var test = new SetBackendServiceWithBaseUrl().AsTestDocument();
+
+        test.RunOutbound();
+
+        test.Context.Api.ServiceUrl.Host.Should().Be("outbound-backend.example.com");
+    }
+
+    [TestMethod]
+    public void SetBackendService_BaseUrl_OnError()
+    {
+        var test = new SetBackendServiceWithBaseUrl().AsTestDocument();
+
+        test.RunOnError();
+
+        test.Context.Api.ServiceUrl.Host.Should().Be("error-backend.example.com");
+    }
+
+    [TestMethod]
+    public void SetBackendService_BackendId_ResolvesFromStore()
+    {
+        var test = new SetBackendServiceWithBackendId().AsTestDocument();
+        test.SetupBackendStore().Add("my-backend", "https://resolved-backend.example.com/v2");
+
+        test.RunInbound();
+
+        test.Context.Api.ServiceUrl.Host.Should().Be("resolved-backend.example.com");
+        test.Context.Api.ServiceUrl.Path.Should().Be("/v2");
+    }
+
+    [TestMethod]
+    public void SetBackendService_BackendId_NotFound_Throws()
+    {
+        var test = new SetBackendServiceWithBackendId().AsTestDocument();
+
+        var act = () => test.RunInbound();
+
+        act.Should().Throw<BadRuntimeConfigurationException>()
+            .Which.Message.Should().Contain("my-backend");
+    }
+
+    [TestMethod]
+    public void SetBackendService_Callback()
+    {
+        var test = new SetBackendServiceWithBaseUrl().AsTestDocument();
+        var callbackExecuted = false;
+        test.SetupInbound().SetBackendService().WithCallback((_, config) =>
+        {
+            callbackExecuted = true;
+            config.BaseUrl.Should().Be("https://new-backend.example.com/api");
+        });
+
+        test.RunInbound();
+
+        callbackExecuted.Should().BeTrue();
+        test.Context.Api.ServiceUrl.Host.Should().NotBe("new-backend.example.com");
+    }
+}