Add IValidateOptions for DistributedCacheEventStreamStoreOptions

Author: MackinnonBuck

src/ModelContextProtocol.AspNetCore/DistributedCacheEventStreamStoreOptionsValidator.cs

@@ -0,0 +1,25 @@
+using Microsoft.Extensions.Caching.Distributed;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using ModelContextProtocol.Server;
+
+namespace ModelContextProtocol.AspNetCore;
+
+/// <summary>
+/// Validates that <see cref="DistributedCacheEventStreamStoreOptions.Cache"/> is set.
+/// </summary>
+internal sealed class DistributedCacheEventStreamStoreOptionsValidator : IValidateOptions<DistributedCacheEventStreamStoreOptions>
+{
+    public ValidateOptionsResult Validate(string? name, DistributedCacheEventStreamStoreOptions options)
+    {
+        if (options.Cache is null)
+        {
+            return ValidateOptionsResult.Fail(
+                $"The '{nameof(DistributedCacheEventStreamStoreOptions)}.{nameof(DistributedCacheEventStreamStoreOptions.Cache)}' property must be set. " +
+                $"Register an {nameof(IDistributedCache)} in DI or set the {nameof(DistributedCacheEventStreamStoreOptions.Cache)} property " +
+                $"in the '{nameof(HttpMcpServerBuilderExtensions.WithDistributedCacheEventStreamStore)}' configure callback.");
+        }
+
+        return ValidateOptionsResult.Success;
+    }
+}

src/ModelContextProtocol.AspNetCore/HttpMcpServerBuilderExtensions.cs

@@ -89,6 +89,7 @@ public static IMcpServerBuilder WithDistributedCacheEventStreamStore(this IMcpSe
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<DistributedCacheEventStreamStoreOptions>, DistributedCacheEventStreamStoreOptionsSetup>());
+        builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IValidateOptions<DistributedCacheEventStreamStoreOptions>, DistributedCacheEventStreamStoreOptionsValidator>());
         builder.Services.AddSingleton<ISseEventStreamStore, DistributedCacheEventStreamStore>();
 
         if (configureOptions is not null)

src/ModelContextProtocol/Server/DistributedCacheEventStreamStore.cs

@@ -40,9 +40,7 @@ public DistributedCacheEventStreamStore(IOptions<DistributedCacheEventStreamStor
 
         var optionsValue = options.Value;
         _cache = optionsValue.Cache ?? throw new InvalidOperationException(
-            $"The '{nameof(DistributedCacheEventStreamStoreOptions)}.{nameof(DistributedCacheEventStreamStoreOptions.Cache)}' property must be set. " +
-            $"When using 'WithDistributedCacheEventStreamStore()', the cache will be automatically configured from DI. " +
-            $"When constructing manually, set the '{nameof(DistributedCacheEventStreamStoreOptions.Cache)}' property on the options object.");
+            $"The '{nameof(DistributedCacheEventStreamStoreOptions)}.{nameof(DistributedCacheEventStreamStoreOptions.Cache)}' property must be set.");
         _options = optionsValue;
         _logger = logger ?? NullLogger<DistributedCacheEventStreamStore>.Instance;
     }

tests/ModelContextProtocol.AspNetCore.Tests/HttpMcpServerBuilderExtensionsTests.cs

@@ -61,6 +61,21 @@ public void WithDistributedCacheEventStreamStore_WorksWithoutDICache_WhenCacheSe
         Assert.IsType<DistributedCacheEventStreamStore>(store);
     }
 
+    [Fact]
+    public void WithDistributedCacheEventStreamStore_ThrowsOptionsValidationException_WhenNoCacheConfigured()
+    {
+        Builder.Services
+            .AddMcpServer()
+            .WithHttpTransport()
+            .WithDistributedCacheEventStreamStore();
+
+        using var app = Builder.Build();
+
+        var ex = Assert.Throws<OptionsValidationException>(
+            () => app.Services.GetRequiredService<ISseEventStreamStore>());
+        Assert.StartsWith($"The '{nameof(DistributedCacheEventStreamStoreOptions)}.{nameof(DistributedCacheEventStreamStoreOptions.Cache)}'", ex.Message);
+    }
+
     [Fact]
     public void EventStreamStore_IsPopulatedFromDI_ViaPostConfigure()
     {

tests/ModelContextProtocol.Tests/Server/DistributedCacheEventStreamStoreTests.cs

@@ -34,6 +34,14 @@ public void Constructor_ThrowsArgumentNullException_WhenOptionsIsNull()
         Assert.Throws<ArgumentNullException>("options", () => new DistributedCacheEventStreamStore(null!));
     }
 
+    [Fact]
+    public void Constructor_ThrowsInvalidOperationException_WhenCacheIsNull()
+    {
+        var options = Options.Create(new DistributedCacheEventStreamStoreOptions());
+        var ex = Assert.Throws<InvalidOperationException>(() => new DistributedCacheEventStreamStore(options));
+        Assert.StartsWith($"The '{nameof(DistributedCacheEventStreamStoreOptions)}.{nameof(DistributedCacheEventStreamStoreOptions.Cache)}'", ex.Message);
+    }
+
     [Fact]
     public async Task CreateStreamAsync_ThrowsArgumentNullException_WhenOptionsIsNull()
     {