jellyfin/Emby.Server.Implementations/HttpServer/ResponseFilter.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text;
using MediaBrowser.Controller.Net;
using MediaBrowser.Model.Services;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Microsoft.Net.Http.Headers;

namespace Emby.Server.Implementations.HttpServer
{
    /// <summary>
    /// Class ResponseFilter.
    /// </summary>
    public class ResponseFilter
    {
        private readonly IHttpServer _server;
        private readonly ILogger _logger;

        /// <summary>
        /// Initializes a new instance of the <see cref="ResponseFilter"/> class.
        /// </summary>
        /// <param name="server">The HTTP server.</param>
        /// <param name="logger">The logger.</param>
        public ResponseFilter(IHttpServer server, ILogger logger)
        {
            _server = server;
            _logger = logger;
        }

        /// <summary>
        /// Filters the response.
        /// </summary>
        /// <param name="req">The req.</param>
        /// <param name="res">The res.</param>
        /// <param name="dto">The dto.</param>
        public void FilterResponse(IRequest req, HttpResponse res, object dto)
        {
            foreach(var (key, value) in _server.GetDefaultCorsHeaders(req))
            {
                res.Headers.Add(key, value);
            }
            // Try to prevent compatibility view
            res.Headers["Access-Control-Allow-Headers"] = ("Accept, Accept-Language, Authorization, Cache-Control, " +
                "Content-Disposition, Content-Encoding, Content-Language, Content-Length, Content-MD5, Content-Range, " +
                "Content-Type, Cookie, Date, Host, If-Match, If-Modified-Since, If-None-Match, If-Unmodified-Since, " +
                "Origin, OriginToken, Pragma, Range, Slug, Transfer-Encoding, Want-Digest, X-MediaBrowser-Token, " +
                "X-Emby-Authorization");

            if (dto is Exception exception)
            {
                _logger.LogError(exception, "Error processing request for {RawUrl}", req.RawUrl);

                if (!string.IsNullOrEmpty(exception.Message))
                {
                    var error = exception.Message.Replace(Environment.NewLine, " ", StringComparison.Ordinal);
                    error = RemoveControlCharacters(error);

                    res.Headers.Add("X-Application-Error-Code", error);
                }
            }

            if (dto is IHasHeaders hasHeaders)
            {
                if (!hasHeaders.Headers.ContainsKey(HeaderNames.Server))
                {
                    hasHeaders.Headers[HeaderNames.Server] = "Microsoft-NetCore/2.0, UPnP/1.0 DLNADOC/1.50";
                }

                // Content length has to be explicitly set on on HttpListenerResponse or it won't be happy
                if (hasHeaders.Headers.TryGetValue(HeaderNames.ContentLength, out string contentLength)
                    && !string.IsNullOrEmpty(contentLength))
                {
                    var length = long.Parse(contentLength, CultureInfo.InvariantCulture);

                    if (length > 0)
                    {
                        res.ContentLength = length;
                    }
                }
            }
        }

        /// <summary>
        /// Removes the control characters.
        /// </summary>
        /// <param name="inString">The in string.</param>
        /// <returns>System.String.</returns>
        public static string RemoveControlCharacters(string inString)
        {
            if (inString == null)
            {
                return null;
            }
            else if (inString.Length == 0)
            {
                return inString;
            }

            var newString = new StringBuilder(inString.Length);

            foreach (var ch in inString)
            {
                if (!char.IsControl(ch))
                {
                    newString.Append(ch);
                }
            }

            return newString.ToString();
        }
    }
}