ObjectResultExecutor.cs

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Formatters;
using Microsoft.AspNetCore.Mvc.Internal;
using Microsoft.Extensions.Logging;

namespace Microsoft.AspNetCore.Mvc.Infrastructure
{
    /// <summary>
    /// Executes an <see cref="ObjectResult"/> to write to the response.
    /// </summary>
    public class ObjectResultExecutor : IActionResultExecutor<ObjectResult>
    {
        /// <summary>
        /// Creates a new <see cref="ObjectResultExecutor"/>.
        /// </summary>
        /// <param name="formatterSelector">The <see cref="OutputFormatterSelector"/>.</param>
        /// <param name="writerFactory">The <see cref="IHttpResponseStreamWriterFactory"/>.</param>
        /// <param name="loggerFactory">The <see cref="ILoggerFactory"/>.</param>
        public ObjectResultExecutor(
            OutputFormatterSelector formatterSelector,
            IHttpResponseStreamWriterFactory writerFactory,
            ILoggerFactory loggerFactory)
        {
            if (formatterSelector == null)
            {
                throw new ArgumentNullException(nameof(formatterSelector));
            }

            if (writerFactory == null)
            {
                throw new ArgumentNullException(nameof(writerFactory));
            }

            if (loggerFactory == null)
            {
                throw new ArgumentNullException(nameof(loggerFactory));
            }

            FormatterSelector = formatterSelector;
            WriterFactory = writerFactory.CreateWriter;
            Logger = loggerFactory.CreateLogger<ObjectResultExecutor>();
        }

        /// <summary>
        /// Gets the <see cref="ILogger"/>.
        /// </summary>
        protected ILogger Logger { get; }

        /// <summary>
        /// Gets the <see cref="OutputFormatterSelector"/>.
        /// </summary>
        protected OutputFormatterSelector FormatterSelector { get; }

        /// <summary>
        /// Gets the writer factory delegate.
        /// </summary>
        protected Func<Stream, Encoding, TextWriter> WriterFactory { get; }

        /// <summary>
        /// Executes the <see cref="ObjectResult"/>.
        /// </summary>
        /// <param name="context">The <see cref="ActionContext"/> for the current request.</param>
        /// <param name="result">The <see cref="ObjectResult"/>.</param>
        /// <returns>
        /// A <see cref="Task"/> which will complete once the <see cref="ObjectResult"/> is written to the response.
        /// </returns>
        public virtual Task ExecuteAsync(ActionContext context, ObjectResult result)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            if (result == null)
            {
                throw new ArgumentNullException(nameof(result));
            }

            // If the user sets the content type both on the ObjectResult (example: by Produces) and Response object,
            // then the one set on ObjectResult takes precedence over the Response object
            if (result.ContentTypes == null || result.ContentTypes.Count == 0)
            {
                var responseContentType = context.HttpContext.Response.ContentType;
                if (!string.IsNullOrEmpty(responseContentType))
                {
                    if (result.ContentTypes == null)
                    {
                        result.ContentTypes = new MediaTypeCollection();
                    }

                    result.ContentTypes.Add(responseContentType);
                }
            }

            var objectType = result.DeclaredType;
            if (objectType == null || objectType == typeof(object))
            {
                objectType = result.Value?.GetType();
            }

            var formatterContext = new OutputFormatterWriteContext(
                context.HttpContext,
                WriterFactory,
                objectType,
                result.Value);

            var selectedFormatter = FormatterSelector.SelectFormatter(
                formatterContext, 
                (IList<IOutputFormatter>)result.Formatters ?? Array.Empty<IOutputFormatter>(), 
                result.ContentTypes);
            if (selectedFormatter == null)
            {
                // No formatter supports this.
                Logger.NoFormatter(formatterContext);

                context.HttpContext.Response.StatusCode = StatusCodes.Status406NotAcceptable;
                return Task.CompletedTask;
            }

            Logger.ObjectResultExecuting(result.Value);

            result.OnFormatting(context);
            return selectedFormatter.WriteAsync(formatterContext);
        }
    }
}