Support returning OpenAPI document in YAML from MapOpenApi (#58616)

* Support returning OpenAPI document in YAML from MapOpenApi

* Update tests and YAML content type

Author: captainsafia

src/OpenApi/sample/Program.cs

@@ -37,6 +37,7 @@
 var app = builder.Build();
 
 app.MapOpenApi();
+app.MapOpenApi("/openapi/{documentName}.yaml");
 if (app.Environment.IsDevelopment())
 {
     app.MapSwaggerUi();

src/OpenApi/src/Extensions/OpenApiEndpointRouteBuilderExtensions.cs

@@ -49,8 +49,16 @@ public static IEndpointConventionBuilder MapOpenApi(this IEndpointRouteBuilder e
                     using var writer = Utf8BufferTextWriter.Get(output);
                     try
                     {
-                        document.Serialize(new OpenApiJsonWriter(writer), documentOptions.OpenApiVersion);
-                        context.Response.ContentType = "application/json;charset=utf-8";
+                        if (UseYaml(pattern))
+                        {
+                            document.Serialize(new OpenApiYamlWriter(writer), documentOptions.OpenApiVersion);
+                            context.Response.ContentType = "text/plain+yaml;charset=utf-8";
+                        }
+                        else
+                        {
+                            document.Serialize(new OpenApiJsonWriter(writer), documentOptions.OpenApiVersion);
+                            context.Response.ContentType = "application/json;charset=utf-8";
+                        }
                         await context.Response.BodyWriter.WriteAsync(output.ToArray(), context.RequestAborted);
                         await context.Response.BodyWriter.FlushAsync(context.RequestAborted);
                     }
@@ -63,4 +71,8 @@ public static IEndpointConventionBuilder MapOpenApi(this IEndpointRouteBuilder e
                 }
             }).ExcludeFromDescription();
     }
+
+    private static bool UseYaml(string pattern) =>
+        pattern.EndsWith(".yaml", StringComparison.OrdinalIgnoreCase) ||
+        pattern.EndsWith(".yml", StringComparison.OrdinalIgnoreCase);
 }

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

@@ -29,11 +29,13 @@ public void MapOpenApi_ReturnsEndpointConventionBuilder()
         Assert.IsAssignableFrom<IEndpointConventionBuilder>(returnedBuilder);
     }
 
-    [Fact]
-    public void MapOpenApi_SupportsCustomizingPath()
+    [Theory]
+    [InlineData("/custom/{documentName}/openapi.json")]
+    [InlineData("/custom/{documentName}/openapi.yaml")]
+    [InlineData("/custom/{documentName}/openapi.yml")]
+    public void MapOpenApi_SupportsCustomizingPath(string expectedPath)
     {
         // Arrange
-        var expectedPath = "/custom/{documentName}/openapi.json";
         var serviceProvider = CreateServiceProvider();
         var builder = new DefaultEndpointRouteBuilder(new ApplicationBuilder(serviceProvider));
 
@@ -72,13 +74,17 @@ public async Task MapOpenApi_ReturnsRenderedDocument()
         });
     }
 
-    [Fact]
-    public async Task MapOpenApi_ReturnsDefaultDocumentIfNoNameProvided()
+    [Theory]
+    [InlineData("/openapi.json", "application/json;charset=utf-8", false)]
+    [InlineData("/openapi.toml", "application/json;charset=utf-8", false)]
+    [InlineData("/openapi.yaml", "text/plain+yaml;charset=utf-8", true)]
+    [InlineData("/openapi.yml", "text/plain+yaml;charset=utf-8", true)]
+    public async Task MapOpenApi_ReturnsDefaultDocumentIfNoNameProvided(string expectedPath, string expectedContentType, bool isYaml)
     {
         // Arrange
         var serviceProvider = CreateServiceProvider();
         var builder = new DefaultEndpointRouteBuilder(new ApplicationBuilder(serviceProvider));
-        builder.MapOpenApi("/openapi.json");
+        builder.MapOpenApi(expectedPath);
         var context = new DefaultHttpContext();
         var responseBodyStream = new MemoryStream();
         context.Response.Body = responseBodyStream;
@@ -91,6 +97,11 @@ public async Task MapOpenApi_ReturnsDefaultDocumentIfNoNameProvided()
 
         // Assert
         Assert.Equal(StatusCodes.Status200OK, context.Response.StatusCode);
+        Assert.Equal(expectedContentType, context.Response.ContentType);
+        var responseString = Encoding.UTF8.GetString(responseBodyStream.ToArray());
+        // String check to validate that generated document starts with YAML syntax
+        Assert.Equal(isYaml, responseString.StartsWith("openapi: 3.0.1", StringComparison.OrdinalIgnoreCase));
+        responseBodyStream.Position = 0;
         ValidateOpenApiDocument(responseBodyStream, document =>
         {
             Assert.Equal("OpenApiEndpointRouteBuilderExtensionsTests | v1", document.Info.Title);
@@ -121,16 +132,19 @@ public async Task MapOpenApi_Returns404ForUnresolvedDocument()
         Assert.Equal("No OpenAPI document with the name 'v2' was found.", Encoding.UTF8.GetString(responseBodyStream.ToArray()));
     }
 
-    [Fact]
-    public async Task MapOpenApi_ReturnsDocumentIfNameProvidedInQuery()
+    [Theory]
+    [InlineData("/openapi.json", "application/json;charset=utf-8", false)]
+    [InlineData("/openapi.yaml", "text/plain+yaml;charset=utf-8", true)]
+    [InlineData("/openapi.yml", "text/plain+yaml;charset=utf-8", true)]
+    public async Task MapOpenApi_ReturnsDocumentIfNameProvidedInQuery(string expectedPath, string expectedContentType, bool isYaml)
     {
         // Arrange
         var documentName = "v2";
         var hostEnvironment = new HostEnvironment() { ApplicationName = nameof(OpenApiEndpointRouteBuilderExtensionsTests) };
         var serviceProviderIsService = new ServiceProviderIsService();
         var serviceProvider = CreateServiceProvider(documentName);
         var builder = new DefaultEndpointRouteBuilder(new ApplicationBuilder(serviceProvider));
-        builder.MapOpenApi("/openapi.json");
+        builder.MapOpenApi(expectedPath);
         var context = new DefaultHttpContext();
         var responseBodyStream = new MemoryStream();
         context.Response.Body = responseBodyStream;
@@ -144,6 +158,11 @@ public async Task MapOpenApi_ReturnsDocumentIfNameProvidedInQuery()
 
         // Assert
         Assert.Equal(StatusCodes.Status200OK, context.Response.StatusCode);
+        Assert.Equal(expectedContentType, context.Response.ContentType);
+        var responseString = Encoding.UTF8.GetString(responseBodyStream.ToArray());
+        // String check to validate that generated document starts with YAML syntax
+        Assert.Equal(isYaml, responseString.StartsWith("openapi: 3.0.1", StringComparison.OrdinalIgnoreCase));
+        responseBodyStream.Position = 0;
         ValidateOpenApiDocument(responseBodyStream, document =>
         {
             Assert.Equal($"OpenApiEndpointRouteBuilderExtensionsTests | {documentName}", document.Info.Title);