使用控制器動作篩選器捕獲HTML輸出

Question

我在捕獲HTML輸出的動作上使用以下篩選器，將其轉換爲字符串，執行一些操作以修改字符串，並返回帶有新的ContentResult串。不幸的是，我一直以空字符串結束。

private class UpdateFilter : ActionFilterAttribute 
    { 
     private Stream stream; 

     public override void OnActionExecuting(ActionExecutingContext filterContext) 
     { 
      stream = filterContext.HttpContext.Response.Filter; 
      stream = new MemoryStream(); 
      filterContext.HttpContext.Response.Filter = stream; 
     } 

     public override void OnResultExecuted(ResultExecutedContext filterContext) 
     { 
      StreamReader responsereader = new StreamReader(filterContext.HttpContext.Response.Filter); //empty stream? why? 
      responsereader.BaseStream.Position = 0; 
      string response = responsereader.ReadToEnd(); 
      ContentResult contres = new ContentResult(); 
      contres.Content = response; 
      filterContext.Result = contres; 
     } 
    } 

我牽制是的StreamReader（流）.ReadToEnd（）返回一個空字符串，但我想不出爲什麼。

任何想法如何解決這個問題？

編輯：我已經將OnActionExecuted更改爲OnResultExecuted，現在它在View生成後調用，但流仍然是空的！

Answer 1

我解決了這個由劫持HttpWriter，並將其寫入StringBuilder而不是響應，然後在將響應寫入輸出之前對響應進行任何處理。

private class UpdateFilter : ActionFilterAttribute 
    { 
     private HtmlTextWriter tw; 
     private StringWriter sw; 
     private StringBuilder sb; 
     private HttpWriter output; 

     public override void OnActionExecuting(ActionExecutingContext filterContext) 
     { 
      sb = new StringBuilder(); 
      sw = new StringWriter(sb); 
      tw = new HtmlTextWriter(sw); 
      output = (HttpWriter)filterContext.RequestContext.HttpContext.Response.Output; 
      filterContext.RequestContext.HttpContext.Response.Output = tw; 
     } 

     public override void OnResultExecuted(ResultExecutedContext filterContext) 
     { 
      string response = sb.ToString(); 
      //response processing 
      output.Write(response); 
     } 
    } 

Answer 2

在讀取它之前，嘗試通過設置Position = 0;來倒回流。

public override void OnActionExecuted(ActionExecutedContext filterContext) 
{ 
    stream.Position = 0; 
    string response = new StreamReader(stream).ReadToEnd(); 
    ContentResult contres = new ContentResult(); 
    contres.Content = response; 
    filterContext.Result = contres; 
} 

Answer 3

你可以在OnActionExectuted方法中驗證流是否爲NULL？我不知道流變量的狀態被存儲整個過程..

你爲什麼不嘗試讓流出來的filterContext的：

public override void OnActionExecuted(ActionExecutedContext filterContext) 
{ 
    var stream = filterContext.HttpContext.Response.Filter; 
    string response = new StreamReader(stream).ReadToEnd(); 
    ContentResult contres = new ContentResult(); 
    contres.Content = response; 
    filterContext.Result = contres; 
} 

Answer 4

我想我已經開發了一個很好的方法來做到這一點。

• 與自定義一個
• 該濾波器需要委託接受一個流
• 此委託，因此抽象方法被稱爲該流的靠近一個抽象方法更換效應初探過濾，即當所有的HTML都可用時
• 覆蓋OnClose方法並隨意使用流。

---

public abstract class ReadOnlyActionFilterAttribute : ActionFilterAttribute 
{ 
    private delegate void ReadOnlyOnClose(Stream stream); 

    public override void OnActionExecuting(ActionExecutingContext filterContext) 
    { 
     filterContext.HttpContext.Response.Filter = new OnCloseFilter(
      filterContext.HttpContext.Response.Filter, 
      this.OnClose); 
     base.OnActionExecuting(filterContext); 
    } 

    protected abstract void OnClose(Stream stream); 

    private class OnCloseFilter : MemoryStream 
    { 
     private readonly Stream stream; 

     private readonly ReadOnlyOnClose onClose; 

     public OnCloseFilter(Stream stream, ReadOnlyOnClose onClose) 
     { 
      this.stream = stream; 
      this.onClose = onClose; 
     } 

     public override void Close() 
     { 
      this.Position = 0; 
      this.onClose(this); 
      this.Position = 0; 
      this.CopyTo(this.stream); 
      base.Close(); 
     } 
    } 
} 

然後你可以從這個推導到另一個屬性來訪問數據流，並獲得HTML：

public class MyAttribute : ReadOnlyActionFilterAttribute 
{ 
    protected override void OnClose(Stream stream) 
    { 
     var html = new HtmlDocument(); 
     html.Load(stream); 
     // play with html 
    } 
}