与控制器动作过滤器捕获的HTML输出 [英] Capturing HTML output with a controller action filter

问题描述

我得上的操作到位以下筛选捕捉到HTML输出，其转换为字符串，做一些操作，以修改字符串，并用新的字符串返回ContentResult类型，不幸的是，我一直在结束了一个空字符串。

I've got the following filter in place on an action to capture the HTML output, convert it to a string, do some operations to modify the string, and return a ContentResult with the new string. Unfortunately, I keep ending up with an empty string.

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;
        }
    }

我已经牵制了的StreamReader（流）.ReadToEnd（）返回一个空字符串，但我想不出为什么。

I've pinned down that StreamReader(stream).ReadToEnd() returns an empty string, but I can't figure out why.

任何想法如何解决这一问题？

Any ideas how to fix this?

修改：我已经改变了OnActionExecuted到OnResultExecuted，现在已经产生了查看后的叫法，但流仍然是空的。

EDIT: I've changed the OnActionExecuted to OnResultExecuted, and now it is called after the View has been generated, but the stream is still empty!

推荐答案

我解决了这个被劫持HttpWriter，并有记录到一个的StringBuilder 而非响应，然后做任何需要它写入输出前需做/与响应。

I solved this by hijacking the HttpWriter, and having it write into a StringBuilder rather than the response, and then doing whatever needs to be done to/with the response before writing it to the output.

 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);
        }
    }

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