ASP.Net 重写IHttpModule 来拦截 HttpApplication 实现HTML资源压缩和空白过滤

务实直接上代码：

1. 重写FilterModule.cs

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using System.Web;
 using System.Text.RegularExpressions;
 using System.IO.Compression;

 namespace Compress.FilterModule
 {
     public class FilterModule : IHttpModule
     {
         public void Dispose()
         {
             //
         }

         /// <summary>
         /// Init method is only used to register the desired event
         /// </summary>
         /// <param name="context"></param>
         public void Init(HttpApplication context)
         {
             context.BeginRequest += new EventHandler(context_BeginRequest);
             //context.EndRequest += new EventHandler(context_EndRequest);
             //context.PostRequestHandlerExecute += new EventHandler(context_PostRequestHandlerExecute);
         }

         /// <summary>
         /// Handles the BeginRequest event of the context control.
         /// </summary>
         /// <param name="sender">The source of the event.</param>
         /// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
         void context_BeginRequest(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             HttpContext context = app.Context;
             if (context.CurrentHandler is System.Web.UI.Page)
             {
                 bool isPage = context.CurrentHandler.IsReusable;
             }
             if (app.Request.RawUrl.Contains(".aspx") || app.Request.RawUrl.EndsWith("/"))
             {
                 // HttpContext context = app.Context;
                 HttpRequest request = context.Request;
                 string acceptEncoding = request.Headers["Accept-Encoding"];
                 HttpResponse response = context.Response;
                 if (!string.IsNullOrEmpty(acceptEncoding))
                 {
                     acceptEncoding = acceptEncoding.ToUpperInvariant();
                     if (acceptEncoding.Contains("GZIP"))
                     {
                         //var straem = new GZipStream(response.Filter, CompressionMode.Compress);
                         response.Filter = new CompressWhitespaceFilter(response.Filter, CompressOptions.GZip);
                         response.AppendHeader("Content-encoding", "gzip");
                     }
                     else if (acceptEncoding.Contains("DEFLATE"))
                     {
                         response.Filter = new CompressWhitespaceFilter(context.Response.Filter, CompressOptions.Deflate);
                         response.AppendHeader("Content-encoding", "deflate");
                     }
                 }
                 response.Cache.VaryByHeaders["Accept-Encoding"] = true;
             }
         }

         // Test
         //void context_BeginRequest(object sender, EventArgs e)
         //{
         //    HttpApplication application = (HttpApplication)sender;
         //    HttpContext context = application.Context;
         //    context.Response.ContentType = "text/html";
         //    context.Response.Charset = "GB2312";
         //    context.Response.ContentEncoding = Encoding.Default;
         //    context.Response.Write("<h1 style='color:#00f'>Treatment from HttpModule，Begin...</h1><hr>");
         //}

         // Test
         //void context_EndRequest(object sender, EventArgs e)
         //{
         //    HttpApplication application = (HttpApplication)sender;
         //    HttpContext context = application.Context;
         //    context.Response.ContentType = "text/html";
         //    context.Response.Charset = "GB2312";
         //    context.Response.ContentEncoding = Encoding.Default;
         //    context.Response.Write("<hr><h1 style='color:#f00'>Treatment from HttpModule，End...</h1>");
         //}

     }
 }

2. 处理压缩和匹配自定义过滤 CompressWhitespaceFilter.cs

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using System.IO;
 using System.Text;
 using System.Text.RegularExpressions;
 using System.IO.Compression;

 namespace Compress.ModuleDemo
 {
     public enum CompressOptions
     {
         GZip,
         Deflate,
         None
     }

     public class CompressWhitespaceFilter : Stream
     {
         StringBuilder responseHtml;
         const string _cssPattern = "(?<HTML><link[^>]*href\\s*=\\s*[\\\"\\']?(?<HRef>[^\"'>\\s]*)[\\\"\\']?[^>]*>)";
         const string _jsPattern = "(?<HTML><script[^>]*src\\s*=\\s*[\\\"\\']?(?<SRC>[^\"'>\\s]*)[\\\"\\']?[^>]*></script>)";

         private HttpApplication app;
         public HttpApplication App
         {
             get { return app; }
             set { app = value; }
         }

         private GZipStream _contentGZip;
         private DeflateStream _content_Deflate;
         private Stream _content;
         private CompressOptions _options;
         private bool disposed = false;

         private CompressWhitespaceFilter() { }
         public CompressWhitespaceFilter(Stream content, CompressOptions options)
         {

             responseHtml = new StringBuilder();
             if (options == CompressOptions.GZip)
             {
                 this._contentGZip = new GZipStream(content, CompressionMode.Compress, true);
                 this._content = this._contentGZip;
             }
             else if (options == CompressOptions.Deflate)
             {
                 this._content_Deflate = new DeflateStream(content, CompressionMode.Compress, true);
                 this._content = this._content_Deflate;
             }
             else
             {
                 this._content = content;
             }
             this._options = options;
         }

         public override bool CanRead
         {
             get { return this._content.CanRead; }
         }

         public override bool CanSeek
         {
             get { return this._content.CanSeek; }
         }

         public override bool CanWrite
         {
             get { return this._content.CanWrite; }
         }

         /// <summary>
         /// When overriding in a derived class, all buffers of the stream are cleared and all buffer data is written to the underlying device
         /// </summary>
         public override void Flush()
         {
             this._content.Flush();
             //Test
             //this._content.Dispose();
             //this._contentGZip.Dispose();
         }

         /// <summary>
         /// 重写Dispose方法，释放派生类自己的资源，并且调用基类的Dispose方法
         /// 使Gzip把缓存中余下的内容全部写入MemoryStream中,因为只有在Gzip流释放之后才能去承载对象中读取数据或判断数据大小
         /// </summary>
         /// <param name="disposing"></param>
         protected override void Dispose(bool disposing)
         {
             if (!this.disposed)
             {
                 try
                 {
                     if (disposing)
                     {
                         // Release the managed resources you added in this derived class here.
                         //xx.Dispose();
                     }

                     //  Release the native unmanaged resources you added in this derived class here.
                     //  xx.Close()

                     //if (_contentGZip != null)
                     //    _contentGZip.Close();

                     //if (_content_Deflate != null)
                     //    _content_Deflate.Close();

                     this._content.Close();
                     this.disposed = true;
                 }
                 finally
                 {
                     // Call Dispose on your base class.
                     base.Dispose(disposing);
                 }
             }
         }

         public override long Length
         {
             get { return this._content.Length; }
         }

         public override long Position
         {
             get
             {
                 return this._content.Position;
             }
             set
             {
                 this._content.Position = value;
             }
         }

         public override int Read(byte[] buffer, int offset, int count)
         {
             return this._content.Read(buffer, offset, count);
         }

         public override long Seek(long offset, SeekOrigin origin)
         {
             return this._content.Seek(offset, origin);
         }

         public override void SetLength(long value)
         {
             this._content.SetLength(value);
         }

         public override void Write(byte[] buffer, int offset, int count)
         {
             byte[] data = new byte[count + ];
             Buffer.BlockCopy(buffer, offset, data, , count);
             string s = System.Text.Encoding.UTF8.GetString(data);
             s = Regex.Replace(s, "^\\s*", string.Empty, RegexOptions.Compiled | RegexOptions.Multiline);
             s = Regex.Replace(s, "\\r\\n", string.Empty, RegexOptions.Compiled | RegexOptions.Multiline);
             s = Regex.Replace(s, "<!--*.*?-->", string.Empty, RegexOptions.Compiled | RegexOptions.Multiline);
             byte[] outdata = System.Text.Encoding.UTF8.GetBytes(s);
             this._content.Write(outdata, , outdata.GetLength());
         }

         /// <summary>
         /// Replcase stylesheet links with ones pointing to HttpHandlers that compress and cache the css
         /// </summary>
         /// <param name="html"></param>
         /// <returns></returns>
         public string ReplaceCss(string html)
         {
             // create a list of the stylesheets
             List<string> stylesheets = new List<string>();
             // create a dictionary used for combining css in the same directory
             Dictionary<string, List<string>> css = new Dictionary<string, List<string>>();

             // create a base uri which will be used to get the uris to the css
             Uri baseUri = new Uri(app.Request.Url.AbsoluteUri);

             // loop through each match
             foreach (Match match in Regex.Matches(html, _cssPattern, RegexOptions.IgnoreCase))
             {
                 // this is the enire match and will be used to replace the link
                 string linkHtml = match.Groups[].Value;
                 // this is the href of the link
                 string href = match.Groups[].Value;

                 // get a uri from the base uri, this will resolve any relative and absolute links
                 Uri uri = new Uri(baseUri, href);
                 string file = "";
                 // check to see if it is a link to a local file
                 if (uri.Host == baseUri.Host)
                 {
                     // check to see if it is local to the application
                     if (uri.AbsolutePath.ToLower().StartsWith(app.Context.Request.ApplicationPath.ToLower()))
                     {
                         // this combines css files in the same directory into one file (actual combining done in HttpHandler)
                         int index = uri.AbsolutePath.LastIndexOf("/");
                         string path = uri.AbsolutePath.Substring(, index + );
                         file = uri.AbsolutePath.Substring(index + );
                         if (!css.ContainsKey(path))
                             css.Add(path, new List<string>());
                         css[path].Add(file + (href.Contains("?") ? href.Substring(href.IndexOf("?")) : ""));
                         // replace the origianl links with blanks
                         html = html.Replace(linkHtml, "");
                         // continue to next link
                         continue;
                     }
                     else
                         file = uri.AbsolutePath + uri.Query;
                 }
                 else
                     file = uri.AbsoluteUri;
                 string newLinkHtml = linkHtml.Replace(href, "css.axd?files=" + file);

                 // just replace the link with the new link
                 html = html.Replace(linkHtml, newLinkHtml);
             }

             StringBuilder link = new StringBuilder();
             link.AppendLine("");
             foreach (string key in css.Keys)
             {
                 link.AppendLine(string.Format("<link href='{0}css.axd?files={1}' type='text/css' rel='stylesheet' />", key, string.Join(",", css[key].ToArray())));

             }

             // find the head tag and insert css in the head tag
             int x = html.IndexOf("<head");
             int num = ;
             if (x > -)
             {
                 num = html.Substring(x).IndexOf(">");
                 html = html.Insert(x + num + , link.ToString());
             }
             return html;
         }

         /// <summary>
         /// Replcase javascript links with ones pointing to HttpHandlers that compress and cache the javascript
         /// </summary>
         /// <param name="html"></param>
         /// <returns></returns>
         public string ReplaceJS(string html)
         {
             // if the javascript is in the head section of the html, then try to combine the javascript into one
             int start, end;
             if (html.Contains("<head") && html.Contains("</head>"))
             {
                 start = html.IndexOf("<head");
                 end = html.IndexOf("</head>");
                 string head = html.Substring(start, end - start);

                 head = ReplaceJSInHead(head);

                 html = html.Substring(, start) + head + html.Substring(end);
             }

             // javascript that is referenced in the body is usually used to write content to the page via javascript,
             // we don't want to combine these and place them in the header since it would cause problems
             // or it is a WebResource.axd or ScriptResource.axd
             if (html.Contains("<body") && html.Contains("</body>"))
             {
                 start = html.IndexOf("<body");
                 end = html.IndexOf("</body>");
                 string head = html.Substring(start, end - start);

                 head = ReplaceJSInBody(head);

                 html = html.Substring(, start) + head + html.Substring(end);
             }

             return html;
         }

         /// <summary>
         /// Replaces the js in the head tag. (see ReplaceCss for comments)
         /// </summary>
         /// <param name="html"></param>
         /// <returns></returns>
         public string ReplaceJSInHead(string html)
         {
             List<string> javascript = new List<string>();
             Dictionary<string, List<string>> js = new Dictionary<string, List<string>>();

             Uri baseUri = new Uri(app.Request.Url.AbsoluteUri);
             foreach (Match match in Regex.Matches(html, _jsPattern, RegexOptions.IgnoreCase))
             {
                 string linkHtml = match.Groups[].Value;
                 string src = match.Groups[].Value;

                 Uri uri = new Uri(baseUri, src);
                 if (!Path.GetExtension(uri.AbsolutePath).Equals("js") && uri.AbsolutePath.Contains("WebResource.axd"))
                     continue;
                 if (uri.Host == baseUri.Host)
                 {
                     if (uri.AbsolutePath.ToLower().StartsWith(app.Context.Request.ApplicationPath.ToLower()))
                     {
                         int index = uri.AbsolutePath.LastIndexOf("/");
                         string path = uri.AbsolutePath.Substring(, index + );
                         string file = uri.AbsolutePath.Substring(index + );
                         if (!js.ContainsKey(path))
                             js.Add(path, new List<string>());
                         js[path].Add(file + (src.Contains("?") ? src.Substring(src.IndexOf("?")) : ""));
                     }
                     else
                         javascript.Add(uri.AbsolutePath + uri.Query);

                 }
                 else
                     javascript.Add(uri.AbsoluteUri);
                 html = html.Replace(linkHtml, "");
             }

             int x = html.IndexOf("<head");
             int num = html.Substring(x).IndexOf(">");
             string link = "";

             foreach (string key in js.Keys)
             {
                 link = string.Format("<script src='{0}js.axd?files={1}' type='text/javascript' ></script>", key, string.Join(",", js[key].ToArray()));
                 html = html.Insert(x + num + , link + Environment.NewLine);

             }
             if (javascript.Count > )
             {
                 link = string.Format("<script src='js.axd?files={0}' type='text/javascript' /></script>", string.Join(",", javascript.ToArray()));
                 html = html.Insert(x + num + , link + Environment.NewLine);
             }
             return html;
         }

         /// <summary>
         /// Replaces the js in the body. (see ReplaceCss for comments)
         /// </summary>
         /// <param name="html"></param>
         /// <returns></returns>
         public string ReplaceJSInBody(string html)
         {
             Uri baseUri = new Uri(app.Request.Url.AbsoluteUri);
             foreach (Match match in Regex.Matches(html, _jsPattern, RegexOptions.IgnoreCase))
             {
                 string linkHtml = match.Groups[].Value;
                 string src = match.Groups[].Value;

                 Uri uri = new Uri(baseUri, src);
                 if (!uri.AbsolutePath.EndsWith(".js") && !uri.AbsolutePath.Contains("WebResource.axd"))
                     continue;
                 string file = "";
                 string path = "";
                 if (uri.Host == baseUri.Host)
                 {
                     if (uri.AbsolutePath.ToLower().StartsWith(app.Context.Request.ApplicationPath.ToLower()))
                     {
                         int index = uri.AbsolutePath.LastIndexOf("/");
                         path = uri.AbsolutePath.Substring(, index + );
                         file = uri.AbsolutePath.Substring(index + ) + (src.Contains("?") ? src.Substring(src.IndexOf("?")) : "");
                     }
                     else
                         file = uri.AbsolutePath + uri.Query;
                 }
                 else
                     file = uri.AbsoluteUri;
                 string newLinkHtml = linkHtml.Replace(src, path + "js.axd?files=" + file);
                 html = html.Replace(linkHtml, newLinkHtml);
             }
             return html;
         }

     }
 }

在这里需要注意的是对GZIP 的释放，否则流数据会读取不到：

         /// <summary>
         /// 重写Dispose方法，释放派生类自己的资源，并且调用基类的Dispose方法
         /// 使Gzip把缓存中余下的内容全部写入MemoryStream中,因为只有在Gzip流释放之后才能去承载对象中读取数据或判断数据大小
         /// </summary>
         /// <param name="disposing"></param>
         protected override void Dispose(bool disposing)
         {
             if (!this.disposed)
             {
                 try
                 {
                     if (disposing)
                     {
                         // Release the managed resources you added in this derived class here.
                         //xx.Dispose();
                     }

                     //  Release the native unmanaged resources you added in this derived class here.
                     //  xx.Close()

                     //if (_contentGZip != null)
                     //    _contentGZip.Close();

                     //if (_content_Deflate != null)
                     //    _content_Deflate.Close();

                     this._content.Close();
                     this.disposed = true;
                 }
                 finally
                 {
                     // Call Dispose on your base class.
                     base.Dispose(disposing);
                 }
             }
         }

对于C#非托管资源释放(Finalize/Dispose)方法理解：

http://www.cnblogs.com/lzhdim/archive/2009/11/04/1595845.html