- Fix breaking binary changes

- code review suggestions

src/Swashbuckle.AspNetCore.Swagger/ISwaggerDocumentSerializer.cs

@@ -4,8 +4,18 @@
 
 namespace Swashbuckle.AspNetCore.Swagger
 {
+    /// <summary>
+    /// Provide an implementation for this interface if you wish to customize how the open api document is exactly written.
+    /// SerializeDocument will be called in that case, instead of the Microsoft built in Serialize methods.
+    /// </summary>
     public interface ISwaggerDocumentSerializer
     {
+        /// <summary>
+        /// Called in the places where normally SerializeV2 or SerializeV3 on OpenApiDocument would be called.
+        /// </summary>
+        /// <param name="document">The open api document that should be serialized</param>
+        /// <param name="writer">The write to which the document needs to be written</param>
+        /// <param name="specVersion">The open api spec to serialize</param>
 		void SerializeDocument(OpenApiDocument document, IOpenApiWriter writer, OpenApiSpecVersion specVersion);
 	}
-}
+}

src/Swashbuckle.AspNetCore.Swagger/SwaggerMiddleware.cs

@@ -6,6 +6,7 @@
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.AspNetCore.Routing.Template;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Writers;
 
@@ -18,6 +19,12 @@ public class SwaggerMiddleware
         private readonly TemplateMatcher _requestMatcher;
         private readonly ISwaggerDocumentSerializer _swaggerDocumentSerializer;
 
+        public SwaggerMiddleware(
+            RequestDelegate next,
+            SwaggerOptions options) : this (next, options, null)
+        {
+        }
+
         public SwaggerMiddleware(
             RequestDelegate next,
             SwaggerOptions options,
@@ -28,7 +35,7 @@ public SwaggerMiddleware(
             _requestMatcher = new TemplateMatcher(TemplateParser.Parse(_options.RouteTemplate), new RouteValueDictionary());
 
             // Use IServiceProvider to retrieve the ISwaggerDocumentSerializer, because it is an optional service
-            _swaggerDocumentSerializer = serviceProvider.GetService(typeof(ISwaggerDocumentSerializer)) as ISwaggerDocumentSerializer;
+            _swaggerDocumentSerializer = serviceProvider?.GetService<ISwaggerDocumentSerializer>();
         }
 
         public async Task Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)

src/Swashbuckle.AspNetCore.SwaggerGen/DependencyInjection/DocumentProvider.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
 using Microsoft.OpenApi.Writers;
 using Swashbuckle.AspNetCore.Swagger;
@@ -27,6 +28,13 @@ internal class DocumentProvider : IDocumentProvider
         private readonly IAsyncSwaggerProvider _swaggerProvider;
         private readonly ISwaggerDocumentSerializer _swaggerDocumentSerializer;
 
+        public DocumentProvider(
+            IOptions<SwaggerGeneratorOptions> generatorOptions,
+            IOptions<SwaggerOptions> options,
+            IAsyncSwaggerProvider swaggerProvider
+            ) : this(generatorOptions, options, swaggerProvider, null)
+        { }
+
         public DocumentProvider(
             IOptions<SwaggerGeneratorOptions> generatorOptions,
             IOptions<SwaggerOptions> options,
@@ -39,7 +47,7 @@ IServiceProvider serviceProvider
             _swaggerProvider = swaggerProvider;
 
             // Use IServiceProvider to retrieve the ISwaggerDocumentSerializer, because it is an optional service
-            _swaggerDocumentSerializer = serviceProvider.GetService(typeof(ISwaggerDocumentSerializer)) as ISwaggerDocumentSerializer;
+            _swaggerDocumentSerializer = serviceProvider?.GetService<ISwaggerDocumentSerializer>();
         }
 
         public IEnumerable<string> GetDocumentNames()