c# - 不允许过滤

我已经实现了一个操作方法来缩小HTML，它给出了一个例外“不允许过滤”，我已经搜索了Internet，但找不到任何合适的解决方案。请指导我如何解决这个问题。我正在共享我的代码：
minifyattribute类：

public class MinifyAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {

        var request = filterContext.HttpContext.Request;
        var response = filterContext.HttpContext.Response;

        response.Filter = new Minify(response.Filter, s =>
        {
            s = Regex.Replace(s, @"\s+", " ");
            s = Regex.Replace(s, @"\s*\n\s*", "\n");
            s = Regex.Replace(s, @"\s*\>\s*\<\s*", "><");
            s = Regex.Replace(s, @"<!--(.*?)-->", "");   //Remove comments

            var firstEndBracketPosition = s.IndexOf(">");
            if (firstEndBracketPosition >= 0)
            {
                s = s.Remove(firstEndBracketPosition, 1);
                s = s.Insert(firstEndBracketPosition, ">");
            }
            return s;
        }); // i'm getting exception here on this code block

    }
}

缩小班级

public class Minify : Stream
    {
        private Stream _shrink;
        private Func<string, string> _filter;

        public Minify(Stream shrink, Func<string, string> filter)
        {
            _shrink = shrink;
            _filter = filter;
        }


        public override bool CanRead { get { return true; } }
        public override bool CanSeek { get { return true; } }
        public override bool CanWrite { get { return true; } }
        public override void Flush() { _shrink.Flush(); }
        public override long Length { get { return 0; } }
        public override long Position { get; set; }
        public override int Read(byte[] buffer, int offset, int count)
        {
            return _shrink.Read(buffer, offset, count);
        }
        public override long Seek(long offset, SeekOrigin origin)
        {
            return _shrink.Seek(offset, origin);
        }
        public override void SetLength(long value)
        {
            _shrink.SetLength(value);
        }
        public override void Close()
        {
            _shrink.Close();
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            // capture the data and convert to string
            byte[] data = new byte[count];
            Buffer.BlockCopy(buffer, offset, data, 0, count);
            string s = Encoding.Default.GetString(buffer);

            // filter the string
            s = _filter(s);

            // write the data to stream
            byte[] outdata = Encoding.Default.GetBytes(s);
            _shrink.Write(outdata, 0, outdata.GetLength(0));
        }


    }

我在Controller上调用此方法并获取异常

最佳答案

尝试在应用筛选器之前添加空检查：

public override void OnActionExecuting(ActionExecutingContext filterContext)
{
    var response = filterContext.HttpContext.Response;

    if (response.Filter == null) return; // <-----

    response.Filter = new YourFilter(response.Filter);
}