Use TryAddEnumerable for McpServerOptionsSetup

src/ModelContextProtocol/Configuration/McpServerServiceCollectionExtensions.cs

@@ -1,5 +1,6 @@
 using ModelContextProtocol.Server;
 using Microsoft.Extensions.Options;
+using Microsoft.Extensions.DependencyInjection.Extensions;
 
 namespace Microsoft.Extensions.DependencyInjection;
 
@@ -17,7 +18,7 @@ public static class McpServerServiceCollectionExtensions
     public static IMcpServerBuilder AddMcpServer(this IServiceCollection services, Action<McpServerOptions>? configureOptions = null)
     {
         services.AddOptions();
-        services.AddTransient<IConfigureOptions<McpServerOptions>, McpServerOptionsSetup>();
+        services.TryAddEnumerable(ServiceDescriptor.Transient<IConfigureOptions<McpServerOptions>, McpServerOptionsSetup>());
         if (configureOptions is not null)
         {
             services.Configure(configureOptions);

tests/ModelContextProtocol.Tests/SseIntegrationTests.cs

@@ -10,6 +10,7 @@
 using ModelContextProtocol.Server;
 using ModelContextProtocol.Tests.Utils;
 using ModelContextProtocol.Utils.Json;
+using TestServerWithHosting.Tools;
 
 namespace ModelContextProtocol.Tests;
 
@@ -95,6 +96,56 @@ public async Task ConnectAndReceiveNotification_InMemoryServer()
         Assert.Equal("Hello from server!", message);
     }
 
+    [Fact]
+    public async Task AddMcpServer_CanBeCalled_MultipleTimes()
+    {
+        var firstOptionsCallbackCallCount = 0;
+        var secondOptionsCallbackCallCount = 0;
+
+        Builder.Services.AddMcpServer(options =>
+            {
+                Interlocked.Increment(ref firstOptionsCallbackCallCount);
+            })
+            .WithTools<EchoTool>();
+
+        Builder.Services.AddMcpServer(options =>
+            {
+                Interlocked.Increment(ref secondOptionsCallbackCallCount);
+            })
+            .WithTools<SampleLlmTool>();
+
+
+        await using var app = Builder.Build();
+        app.MapMcp();
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        using var httpClient = CreateHttpClient();
+        await using var mcpClient = await ConnectMcpClient(httpClient);
+
+        // Options can be lazily initialized, but they must be instantiated by the time an MCP client can finish connecting.
+        // Callbacks can be called multiple times if configureOptionsAsync is configured, because that uses the IOptionsFactory,
+        // but that's not the case in this test.
+        Assert.Equal(1, firstOptionsCallbackCallCount);
+        Assert.Equal(1, secondOptionsCallbackCallCount);
+
+        var tools = await mcpClient.ListToolsAsync(cancellationToken: TestContext.Current.CancellationToken);
+
+        Assert.Equal(2, tools.Count);
+        Assert.Contains(tools, tools => tools.Name == "Echo");
+        Assert.Contains(tools, tools => tools.Name == "sampleLLM");
+
+        var echoResponse = await mcpClient.CallToolAsync(
+            "Echo",
+            new Dictionary<string, object?>
+            {
+                ["message"] = "from client!"
+            },
+            cancellationToken: TestContext.Current.CancellationToken);
+        var textContent = Assert.Single(echoResponse.Content, c => c.Type == "text");
+
+        Assert.Equal("hello from client!", textContent.Text);
+    }
+
     private static void MapAbsoluteEndpointUriMcp(IEndpointRouteBuilder endpoints)
     {
         var loggerFactory = endpoints.ServiceProvider.GetRequiredService<ILoggerFactory>();