Change OpenAPI document name resolution to be case-insensitive

src/OpenApi/src/Extensions/OpenApiEndpointRouteBuilderExtensions.cs

@@ -30,16 +30,22 @@ public static IEndpointConventionBuilder MapOpenApi(this IEndpointRouteBuilder e
         var options = endpoints.ServiceProvider.GetRequiredService<IOptionsMonitor<OpenApiOptions>>();
         return endpoints.MapGet(pattern, async (HttpContext context, string documentName = OpenApiConstants.DefaultDocumentName) =>
             {
+                // We need to retrieve the document name in a case-insensitive manner
+                // to support case-insensitive document name resolution.
+                // Keyed Services are case-sensitive by default, which doesn't work well for document names in ASP.NET Core
+                // as routing in ASP.NET Core is case-insensitive by default.
+                var lowercasedDocumentName = documentName.ToLowerInvariant();
+
                 // It would be ideal to use the `HttpResponseStreamWriter` to
                 // asynchronously write to the response stream here but Microsoft.OpenApi
                 // does not yet support async APIs on their writers.
                 // See https://github.com/microsoft/OpenAPI.NET/issues/421 for more info.
-                var documentService = context.RequestServices.GetKeyedService<OpenApiDocumentService>(documentName);
+                var documentService = context.RequestServices.GetKeyedService<OpenApiDocumentService>(lowercasedDocumentName);
                 if (documentService is null)
                 {
                     context.Response.StatusCode = StatusCodes.Status404NotFound;
                     context.Response.ContentType = "text/plain;charset=utf-8";
-                    await context.Response.WriteAsync($"No OpenAPI document with the name '{documentName}' was found.");
+                    await context.Response.WriteAsync($"No OpenAPI document with the name '{lowercasedDocumentName}' was found.");
                 }
                 else
                 {

src/OpenApi/src/Extensions/OpenApiServiceCollectionExtensions.cs

@@ -57,13 +57,35 @@ public static IServiceCollection AddOpenApi(this IServiceCollection services, st
         ArgumentNullException.ThrowIfNull(services);
         ArgumentNullException.ThrowIfNull(configureOptions);
 
-        services.AddOpenApiCore(documentName);
-        services.Configure<OpenApiOptions>(documentName, options =>
+        // We need to store the document name in a case-insensitive manner
+        // to support case-insensitive document name resolution.
+        // Keyed Services are case-sensitive by default, which doesn't work well for document names in ASP.NET Core
+        // as routing in ASP.NET Core is case-insensitive by default.
+        var lowercasedDocumentName = documentName.ToLowerInvariant();
+
+        AddOpenApiCore(services, lowercasedDocumentName);
+        services.Configure<OpenApiOptions>(lowercasedDocumentName, options =>
         {
-            options.DocumentName = documentName;
+            options.DocumentName = lowercasedDocumentName;
             configureOptions(options);
         });
         return services;
+
+        // The reason this method is a local function is to prevent case-sensitive document names being passed into this method (from other methods) in the future.
+        static IServiceCollection AddOpenApiCore(IServiceCollection services, string documentName)
+        {
+            services.AddEndpointsApiExplorer();
+            services.AddKeyedSingleton<OpenApiSchemaService>(documentName);
+            services.AddKeyedSingleton<OpenApiSchemaStore>(documentName);
+            services.AddKeyedSingleton<OpenApiDocumentService>(documentName);
+            // Required for build-time generation
+            services.AddSingleton<IDocumentProvider, OpenApiDocumentProvider>();
+            // Required to resolve document names for build-time generation
+            services.AddSingleton(new NamedService<OpenApiDocumentService>(documentName));
+            // Required to support JSON serializations
+            services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<JsonOptions>, OpenApiSchemaJsonOptions>());
+            return services;
+        }
     }
 
     /// <summary>
@@ -99,19 +121,4 @@ public static IServiceCollection AddOpenApi(this IServiceCollection services, Ac
     /// </example>
     public static IServiceCollection AddOpenApi(this IServiceCollection services)
         => services.AddOpenApi(OpenApiConstants.DefaultDocumentName);
-
-    private static IServiceCollection AddOpenApiCore(this IServiceCollection services, string documentName)
-    {
-        services.AddEndpointsApiExplorer();
-        services.AddKeyedSingleton<OpenApiSchemaService>(documentName);
-        services.AddKeyedSingleton<OpenApiSchemaStore>(documentName);
-        services.AddKeyedSingleton<OpenApiDocumentService>(documentName);
-        // Required for build-time generation
-        services.AddSingleton<IDocumentProvider, OpenApiDocumentProvider>();
-        // Required to resolve document names for build-time generation
-        services.AddSingleton(new NamedService<OpenApiDocumentService>(documentName));
-        // Required to support JSON serializations
-        services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<JsonOptions>, OpenApiSchemaJsonOptions>());
-        return services;
-    }
 }

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Extensions/OpenApiEndpointRouteBuilderExtensionsTests.cs

@@ -59,7 +59,7 @@ public async Task MapOpenApi_ReturnsRenderedDocument()
         context.Response.Body = responseBodyStream;
         context.RequestServices = serviceProvider;
         context.Request.RouteValues.Add("documentName", "v1");
-        var endpoint = builder.DataSources.First().Endpoints.First();
+        var endpoint = builder.DataSources.First().Endpoints[0];
 
         // Act
         var requestDelegate = endpoint.RequestDelegate;
@@ -89,7 +89,7 @@ public async Task MapOpenApi_ReturnsDefaultDocumentIfNoNameProvided(string expec
         var responseBodyStream = new MemoryStream();
         context.Response.Body = responseBodyStream;
         context.RequestServices = serviceProvider;
-        var endpoint = builder.DataSources.First().Endpoints.First();
+        var endpoint = builder.DataSources.First().Endpoints[0];
 
         // Act
         var requestDelegate = endpoint.RequestDelegate;
@@ -121,7 +121,7 @@ public async Task MapOpenApi_Returns404ForUnresolvedDocument()
         context.Response.Body = responseBodyStream;
         context.RequestServices = serviceProvider;
         context.Request.RouteValues.Add("documentName", "v2");
-        var endpoint = builder.DataSources.First().Endpoints.First();
+        var endpoint = builder.DataSources.First().Endpoints[0];
 
         // Act
         var requestDelegate = endpoint.RequestDelegate;
@@ -132,6 +132,30 @@ public async Task MapOpenApi_Returns404ForUnresolvedDocument()
         Assert.Equal("No OpenAPI document with the name 'v2' was found.", Encoding.UTF8.GetString(responseBodyStream.ToArray()));
     }
 
+    [Theory]
+    [InlineData("CaseSensitive", "casesensitive")]
+    [InlineData("casesensitive", "CaseSensitive")]
+    public async Task MapOpenApi_ReturnsDocumentWhenPathIsCaseSensitive(string registeredDocumentName, string requestedDocumentName)
+    {
+        // Arrange
+        var serviceProvider = CreateServiceProvider(registeredDocumentName);
+        var builder = new DefaultEndpointRouteBuilder(new ApplicationBuilder(serviceProvider));
+        builder.MapOpenApi("/openapi/{documentName}.json");
+        var context = new DefaultHttpContext();
+        var responseBodyStream = new MemoryStream();
+        context.Response.Body = responseBodyStream;
+        context.RequestServices = serviceProvider;
+        context.Request.RouteValues.Add("documentName", requestedDocumentName);
+        var endpoint = builder.DataSources.First().Endpoints[0];
+
+        // Act
+        var requestDelegate = endpoint.RequestDelegate;
+        await requestDelegate(context);
+
+        // Assert
+        Assert.Equal(StatusCodes.Status200OK, context.Response.StatusCode);
+    }
+
     [Theory]
     [InlineData("/openapi.json", "application/json;charset=utf-8", false)]
     [InlineData("/openapi.yaml", "text/plain+yaml;charset=utf-8", true)]
@@ -150,7 +174,7 @@ public async Task MapOpenApi_ReturnsDocumentIfNameProvidedInQuery(string expecte
         context.Response.Body = responseBodyStream;
         context.RequestServices = serviceProvider;
         context.Request.QueryString = new QueryString($"?documentName={documentName}");
-        var endpoint = builder.DataSources.First().Endpoints.First();
+        var endpoint = builder.DataSources.First().Endpoints[0];
 
         // Act
         var requestDelegate = endpoint.RequestDelegate;