WebAPI的压缩

有时候为了提升WebAPI的性能，减少响应时间，我们会使用压缩和解压，而现在大多数客户端浏览器都提供了内置的解压支持。在WebAPI请求的资源越大时，使用压缩对性能提升的效果越明显，而当请求的资源很小时则不需要使用压缩和解压，因为压缩和解压同样也是需要耗费一定的时间的。

看见老外写了一篇ASP.NET Web API GZip compression ActionFilter with 8 lines of code

说实话被这标题吸引了，8行代码实现GZip压缩过滤器，我就照着他的去实践了一番，发现居然中文出现乱码。

按照他的实现方式：

1、下载DotNetZipLib库

2、解压后添加Ionic.Zlib.dll的dll引用

3、新建DeflateCompression特性和GZipCompression特性，分别代表Deflate压缩和GZip压缩，这两种压缩方式的实现代码很相似

不同的地方就是

actContext.Response.Content.Headers.Add("Content-encoding", "gzip");

actContext.Response.Content.Headers.Add("Content-encoding", "deflate");

和

  var compressor = new DeflateStream(
                    output, CompressionMode.Compress,
                    CompressionLevel.BestSpeed)

 var compressor = new GZipStream(
                    output, CompressionMode.Compress,
                    CompressionLevel.BestSpeed)

using System.Net.Http;
using System.Web.Http.Filters;

namespace WebAPI.Filter
{
    public class GZipCompressionAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuted(HttpActionExecutedContext actContext)
        {
            var content = actContext.Response.Content;
            var bytes = content == null ? null : content.ReadAsByteArrayAsync().Result;
            var zlibbedContent = bytes == null ? new byte[] :
            CompressionHelper.GZipByte(bytes);
            actContext.Response.Content = new ByteArrayContent(zlibbedContent);
            actContext.Response.Content.Headers.Remove("Content-Type");
            actContext.Response.Content.Headers.Add("Content-encoding", "gzip");
            actContext.Response.Content.Headers.Add("Content-Type", "application/json");
            base.OnActionExecuted(actContext);
        }
    }
}
using System.Net.Http;
using System.Web.Http.Filters;

namespace WebAPI.Filter
{
    public class DeflateCompressionAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuted(HttpActionExecutedContext actContext)
        {
            var content = actContext.Response.Content;
            var bytes = content == null ? null : content.ReadAsByteArrayAsync().Result;
            var zlibbedContent = bytes == null ? new byte[] :
            CompressionHelper.DeflateByte(bytes);
            actContext.Response.Content = new ByteArrayContent(zlibbedContent);
            actContext.Response.Content.Headers.Remove("Content-Type");
            actContext.Response.Content.Headers.Add("Content-encoding", "deflate");
            actContext.Response.Content.Headers.Add("Content-Type", "application/json");
            base.OnActionExecuted(actContext);
        }
    }

4、添加一个压缩帮助类CompressionHelper

using System.IO;
using Ionic.Zlib;

namespace WebAPI.Filter
{
    public class CompressionHelper
    {
        public static byte[] DeflateByte(byte[] str)
        {
            if (str == null)
            {
                return null;
            }

            using (var output = new MemoryStream())
            {
                using (
                    var compressor = new DeflateStream(
                    output, CompressionMode.Compress,
                    CompressionLevel.BestSpeed))
                {
                    compressor.Write(str, , str.Length);
                }

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

                return output.ToArray();
            }
        }
    }
}

5、控制器调用，这里我写的测试代码：

    public class TestController : ApiController
    {
        StringBuilder sb = new StringBuilder();

        [GZipCompression]
        public string Get(int id)
        {
            for (int i = ; i < ;i++ )
            {
                sb.Append("这里是中国的领土" + i);
            }
            return sb.ToString() + DateTime.Now.ToLocalTime() + "," + id;
        }
    }

先看下不使用压缩，注释//[GZipCompression] 标记，文件大小是26.4kb，请求时间是1.27s

使用[GZipCompression]标记，添加压缩后，文件大小是2.4kb，响应时间是1.21，Respouse Body明显小了很多，但是响应时间少得并不明显，因为在本地环境下载太快了，而压缩解压却要消耗一定的时间，界面加载的时间主要消耗在onload上了。有个问题：中文显示乱码了。

使用.net自带的压缩，在System.IO.Compression中提供了对应的类库——GZipStream与DeflateStream。控制器调用代码不变，新建一个CompressContentAttribute.cs类，代码如下：

using System.Web;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;

namespace WebAPI.Filter
{
    // <summary>
    /// 自动识别客户端是否支持压缩，如果支持则返回压缩后的数据
    /// Attribute that can be added to controller methods to force content
    /// to be GZip encoded if the client supports it
    /// </summary>
    public class CompressContentAttribute : ActionFilterAttribute
    {
        /// <summary>
        /// Override to compress the content that is generated by
        /// an action method.
        /// </summary>
        /// <param name="filterContext"></param>
        public override void OnActionExecuting(HttpActionContext filterContext)
        {
            GZipEncodePage();
        }

        /// <summary>
        /// Determines if GZip is supported
        /// </summary>
        /// <returns></returns>
        public static bool IsGZipSupported()
        {
            string AcceptEncoding = HttpContext.Current.Request.Headers["Accept-Encoding"];
            if (!string.IsNullOrEmpty(AcceptEncoding) &&
                    (AcceptEncoding.Contains("gzip") || AcceptEncoding.Contains("deflate")))
                return true;
            return false;
        }

        /// <summary>
        /// Sets up the current page or handler to use GZip through a Response.Filter
        /// IMPORTANT:
        /// You have to call this method before any output is generated!
        /// </summary>
        public static void GZipEncodePage()
        {
            HttpResponse Response = HttpContext.Current.Response;

            if (IsGZipSupported())
            {
                string AcceptEncoding = HttpContext.Current.Request.Headers["Accept-Encoding"];

                if (AcceptEncoding.Contains("deflate"))
                {
                    Response.Filter = new System.IO.Compression.DeflateStream(Response.Filter,
                                               System.IO.Compression.CompressionMode.Compress);
                    #region II6不支持此方法,(实际上此值默认为null 也不需要移除)
                    //Response.Headers.Remove("Content-Encoding");
                    #endregion
                    Response.AppendHeader("Content-Encoding", "deflate");
                }
                else
                {
                    Response.Filter = new System.IO.Compression.GZipStream(Response.Filter,
                                                 System.IO.Compression.CompressionMode.Compress);
                    #region II6不支持此方法,(实际上此值默认为null 也不需要移除)
                    //Response.Headers.Remove("Content-Encoding");
                    #endregion
                    Response.AppendHeader("Content-Encoding", "gzip");
                }
            }

            // Allow proxy servers to cache encoded and unencoded versions separately
            Response.AppendHeader("Vary", "Content-Encoding");
        }
    }

    /// <summary>
    /// 强制Defalte压缩
    /// Content-encoding:gzip，Content-Type:application/json
    /// DEFLATE是一个无专利的压缩算法，它可以实现无损数据压缩，有众多开源的实现算法。
    /// </summary>
    public class DeflateCompressionAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(HttpActionContext filterContext)
        {
            HttpResponse Response = HttpContext.Current.Response;
            Response.Filter = new System.IO.Compression.DeflateStream(Response.Filter,
                                              System.IO.Compression.CompressionMode.Compress);
            #region II6不支持此方法,(实际上此值默认为null 也不需要移除)
            //Response.Headers.Remove("Content-Encoding");
            #endregion
            Response.AppendHeader("Content-Encoding", "deflate");
        }
    }

    /// <summary>
    /// 强制GZip压缩，application/json
    /// Content-encoding:gzip，Content-Type:application/json
    /// GZIP是使用DEFLATE进行压缩数据的另一个压缩库
    /// </summary>
    public class GZipCompressionAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(HttpActionContext filterContext)
        {
            HttpResponse Response = HttpContext.Current.Response;
            Response.Filter = new System.IO.Compression.GZipStream(Response.Filter,
                                              System.IO.Compression.CompressionMode.Compress);
            #region II6不支持此方法,(实际上此值默认为null 也不需要移除)
            //Response.Headers.Remove("Content-Encoding");
            #endregion
            Response.AppendHeader("Content-Encoding", "gzip");
        }
    }
}

运行查看结果，压缩能力比DotNetZipLib略差，但是不再出现乱码了。

把控制器代码中的标记改为   [DeflateCompression]，使用Deflate压缩再来看下效果：

Deflate压缩后，Content-Length值为2538，而GZip压缩Content-Length值为2556，可见Deflate压缩效果更好。

这里，WebAPI的压缩我都是通过Action过滤器的方式来实现，当然你也可以写在WebAPI中的全局配置中，考虑到有些API接口并不需要使用到压缩，所以就通过Action过滤器的方式来实现了。

dudu的这篇文章HttpClient与APS.NET Web API：请求内容的压缩与解压在客户端压缩、在服务端解压。