在Asp.Net WebApi中使用DotNetZip壓縮響應流過濾器

using Ionic.Zlib;
using System;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http.Filters;

namespace WebAPI.Filters
{
    /// <summary>
    /// 壓縮返回信息
    /// </summary>
    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
    public class CompressionFilter : ActionFilterAttribute
    {
        public override Task OnActionExecutedAsync(HttpActionExecutedContext actionExecutedContext, CancellationToken cancellationToken)
        {
            if (actionExecutedContext.Response == null || actionExecutedContext.Request.Method == HttpMethod.Options)
            {
                return DefaultResult(actionExecutedContext, cancellationToken);
            }
            var content = actionExecutedContext.Response.Content;
            if (content == null)
            {
                return DefaultResult(actionExecutedContext, cancellationToken);
            }
            var acceptEncoding = actionExecutedContext.Request.Headers.AcceptEncoding.Where(x => x.Value == "gzip" || x.Value == "deflate").ToList();
            if (acceptEncoding.Count == 0)
            {
                return DefaultResult(actionExecutedContext, cancellationToken);
            }
            var bytes = content.ReadAsByteArrayAsync();
            switch (acceptEncoding[0].Value)
            {
                case "gzip":
                    actionExecutedContext.Response.Content = new ByteArrayContent(CompressionHelper.GZipBytes(bytes.Result));
                    actionExecutedContext.Response.Content.Headers.Add("Content-Encoding", "gzip");
                    break;
                case "deflate":
                    actionExecutedContext.Response.Content = new ByteArrayContent(CompressionHelper.DeflateBytes(bytes.Result));
                    actionExecutedContext.Response.Content.Headers.Add("Content-encoding", "deflate");
                    break;
            }
            return DefaultResult(actionExecutedContext, cancellationToken);
        }
        private Task DefaultResult(HttpActionExecutedContext actionExecutedContext, CancellationToken cancellationToken)
        {
            return base.OnActionExecutedAsync(actionExecutedContext, cancellationToken);
        }
    }

    /// <summary>
    /// 壓縮幫助類
    /// </summary>
    internal static class CompressionHelper
    {
        public static byte[] DeflateBytes(byte[] bytes)
        {
            if (bytes.Length == 0)
            {
                return null;
            }
            using (var output = new MemoryStream())
            {
                using (var compressor = new  DeflateStream(output, CompressionMode.Compress, CompressionLevel.Default))
                {
                    compressor.Write(bytes, 0, bytes.Length);
                }
                return output.ToArray();
            }
        }

        public static byte[] GZipBytes(byte[] bytes)
        {
            if (bytes.Length == 0)
            {
                return null;
            }
            using (var output = new MemoryStream())
            {
                using (var compressor = new GZipStream(output, CompressionMode.Compress, CompressionLevel.Default))
                {
                    compressor.Write(bytes, 0, bytes.Length);
                }
                return output.ToArray();
            }
        }
    }
}