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;
}
}
I've pinned down that StreamReader(stream).ReadToEnd() returns an empty string, but I can't figure out why.
Any ideas how to fix this?
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!
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);
}
}
Above code using the HttpContext to avoid threading errors - see jaminto's comment
private class RenderFilter : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);
HtmlTextWriter tw = new HtmlTextWriter(sw);
HttpWriter output = (HttpWriter)filterContext.RequestContext.HttpContext.Response.Output;
filterContext.HttpContext.Items["sb"] = sb;
filterContext.HttpContext.Items["output"] = output;
filterContext.RequestContext.HttpContext.Response.Output = tw;
}
public override void OnResultExecuted(ResultExecutedContext filterContext)
{
string response = filterContext.HttpContext.Items["sb"].ToString();
//response processing
((HttpWriter)filterContext.HttpContext.Items["output"]).Write(response);
}
}
Try rewinding the stream to the beginning by setting Position = 0;
before you read it.
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;
}
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