Use a hardcoded mcp hostname in derived resource template URIs and ensure built-in resources work with the VS Code client.

Author: eiriktsarpalis

src/ModelContextProtocol.Core/Server/AIFunctionMcpServerResource.cs

@@ -295,7 +295,7 @@ private static string DeriveUriTemplate(string name, AIFunction function)
     {
         StringBuilder template = new();
 
-        template.Append("resource:///").Append(Uri.EscapeDataString(name));
+        template.Append("resource://mcp/").Append(Uri.EscapeDataString(name));
 
         if (function.JsonSchema.TryGetProperty("properties", out JsonElement properties))
         {

tests/ModelContextProtocol.Tests/Configuration/McpServerBuilderExtensionsResourcesTests.cs

@@ -220,7 +220,7 @@ public async Task Throws_When_Resource_Fails()
         await using IMcpClient client = await CreateMcpClientForServer();
 
         await Assert.ThrowsAsync<McpException>(async () => await client.ReadResourceAsync(
-            $"resource:///{nameof(SimpleResources.ThrowsException)}",
+            $"resource://mcp/{nameof(SimpleResources.ThrowsException)}",
             cancellationToken: TestContext.Current.CancellationToken));
     }
 
@@ -268,8 +268,8 @@ public void Register_Resources_From_Current_Assembly()
         sc.AddMcpServer().WithResourcesFromAssembly();
         IServiceProvider services = sc.BuildServiceProvider();
 
-        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResource?.Uri == $"resource:///{nameof(SimpleResources.SomeNeatDirectResource)}");
-        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResourceTemplate?.UriTemplate == $"resource:///{nameof(SimpleResources.SomeNeatTemplatedResource)}{{?name}}");
+        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResource?.Uri == $"resource://mcp/{nameof(SimpleResources.SomeNeatDirectResource)}");
+        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResourceTemplate?.UriTemplate == $"resource://mcp/{nameof(SimpleResources.SomeNeatTemplatedResource)}{{?name}}");
     }
 
     [Fact]
@@ -282,9 +282,9 @@ public void Register_Resources_From_Multiple_Sources()
             .WithResources([McpServerResource.Create(() => "42", new() { UriTemplate = "myResources:///returns42/{something}" })]);
         IServiceProvider services = sc.BuildServiceProvider();
 
-        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResource?.Uri == $"resource:///{nameof(SimpleResources.SomeNeatDirectResource)}");
-        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResourceTemplate?.UriTemplate == $"resource:///{nameof(SimpleResources.SomeNeatTemplatedResource)}{{?name}}");
-        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResourceTemplate?.UriTemplate == $"resource:///{nameof(MoreResources.AnotherNeatDirectResource)}");
+        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResource?.Uri == $"resource://mcp/{nameof(SimpleResources.SomeNeatDirectResource)}");
+        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResourceTemplate?.UriTemplate == $"resource://mcp/{nameof(SimpleResources.SomeNeatTemplatedResource)}{{?name}}");
+        Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResourceTemplate?.UriTemplate == $"resource://mcp/{nameof(MoreResources.AnotherNeatDirectResource)}");
         Assert.Contains(services.GetServices<McpServerResource>(), t => t.ProtocolResourceTemplate.UriTemplate == "myResources:///returns42/{something}");
     }