Fix response code description in Minimal APIs (dotnet#45231)

* Fix response description dotnet#45192

* Test update dotnet#45192

* Use built-in response phrase dictionary dotnet#45192

Author: marcominerva

src/OpenApi/src/OpenApiGenerator.cs

@@ -13,6 +13,7 @@
 using Microsoft.AspNetCore.Mvc.Formatters;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.AspNetCore.Routing.Patterns;
+using Microsoft.AspNetCore.WebUtilities;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Internal;
@@ -192,7 +193,7 @@ private static OpenApiResponses GetOpenApiResponses(MethodInfo method, EndpointM
 
         foreach (var annotation in eligibileAnnotations)
         {
-            var statusCode = annotation.Key.ToString(CultureInfo.InvariantCulture);
+            var statusCode = annotation.Key;
 
             // TODO: Use the discarded response Type for schema generation
             var (_, contentTypes) = annotation.Value;
@@ -203,7 +204,7 @@ private static OpenApiResponses GetOpenApiResponses(MethodInfo method, EndpointM
                 responseContent[contentType] = new OpenApiMediaType();
             }
 
-            responses[statusCode] = new OpenApiResponse
+            responses[statusCode.ToString(CultureInfo.InvariantCulture)] = new OpenApiResponse
             {
                 Content = responseContent,
                 Description = GetResponseDescription(statusCode)
@@ -212,23 +213,8 @@ private static OpenApiResponses GetOpenApiResponses(MethodInfo method, EndpointM
         return responses;
     }
 
-    private static string GetResponseDescription(string statusCode)
-    {
-        if (statusCode.Length != 3)
-        {
-            return string.Empty;
-        }
-        var first = statusCode[0];
-        return first switch
-        {
-            '1' => "Information",
-            '2' => "Success",
-            '3' => "Redirection",
-            '4' => "Client error",
-            '5' => "Server error",
-            _ => string.Empty,
-        };
-    }
+    private static string GetResponseDescription(int statusCode)
+        => ReasonPhrases.GetReasonPhrase(statusCode);
 
     private static void GenerateDefaultContent(MediaTypeCollection discoveredContentTypeAnnotation, Type? discoveredTypeAnnotation)
     {

src/OpenApi/test/OpenApiGeneratorTests.cs

@@ -242,10 +242,10 @@ public void DefaultResponseDescriptionIsCorrect()
         Assert.Equal(2, operation.Responses.Count);
 
         var successResponse = operation.Responses["201"];
-        Assert.Equal("Success", successResponse.Description);
+        Assert.Equal("Created", successResponse.Description);
 
         var clientErrorResponse = operation.Responses["400"];
-        Assert.Equal("Client error", clientErrorResponse.Description);
+        Assert.Equal("Bad Request", clientErrorResponse.Description);
     }
 
     [Fact]
@@ -259,10 +259,10 @@ public void DefaultResponseDescriptionIsCorrectForTwoSimilarResponses()
         Assert.Equal(2, operation.Responses.Count);
 
         var continueResponse = operation.Responses["100"];
-        Assert.Equal("Information", continueResponse.Description);
+        Assert.Equal("Continue", continueResponse.Description);
 
         var switchingProtocolsResponse = operation.Responses["101"];
-        Assert.Equal("Information", switchingProtocolsResponse.Description);
+        Assert.Equal("Switching Protocols", switchingProtocolsResponse.Description);
     }
 
     [Fact]
@@ -279,19 +279,19 @@ public void AllDefaultResponseDescriptions()
         Assert.Equal(5, operation.Responses.Count);
 
         var continueResponse = operation.Responses["100"];
-        Assert.Equal("Information", continueResponse.Description);
+        Assert.Equal("Continue", continueResponse.Description);
 
         var createdResponse = operation.Responses["201"];
-        Assert.Equal("Success", createdResponse.Description);
+        Assert.Equal("Created", createdResponse.Description);
 
         var multipleChoicesResponse = operation.Responses["300"];
-        Assert.Equal("Redirection", multipleChoicesResponse.Description);
+        Assert.Equal("Multiple Choices", multipleChoicesResponse.Description);
 
         var badRequestResponse = operation.Responses["400"];
-        Assert.Equal("Client error", badRequestResponse.Description);
+        Assert.Equal("Bad Request", badRequestResponse.Description);
 
         var InternalServerErrorResponse = operation.Responses["500"];
-        Assert.Equal("Server error", InternalServerErrorResponse.Description);
+        Assert.Equal("Internal Server Error", InternalServerErrorResponse.Description);
     }
 
     [Fact]