Question

我正在尝试通过控制器ActionResult返回大文件，并实现了如下的自定义FileResult类。

    public class StreamedFileResult : FileResult
{
    private string _FilePath;

    public StreamedFileResult(string filePath, string contentType)
        : base(contentType)
    {
        _FilePath = filePath;
    }

    protected override void WriteFile(System.Web.HttpResponseBase response)
    {
        using (FileStream fs = new FileStream(_FilePath, FileMode.Open, FileAccess.Read))
        {
            int bufferLength = 65536;
            byte[] buffer = new byte[bufferLength];
            int bytesRead = 0;

            while (true)
            {
                bytesRead = fs.Read(buffer, 0, bufferLength);

                if (bytesRead == 0)
                {
                    break;
                }

                response.OutputStream.Write(buffer, 0, bytesRead);
            }
        }
    }
}

但是我遇到的问题是整个文件似乎被缓冲到内存中。我需要做些什么来防止这种情况？

Answer 1

您需要刷新响应以防止缓冲。但是，如果您在不设置内容长度的情况下继续缓冲，则用户将看不到任何进度。因此，为了让用户看到正确的进度，IIS缓冲整个内容，计算内容长度，应用压缩然后发送响应。我们采用以下程序将文件传递给客户端，具有很高的性能。

FileInfo path = new FileInfo(filePath);

// user will not see a progress if content-length is not specified
response.AddHeader("Content-Length", path.Length.ToString());
response.Flush();// do not add anymore headers after this...


byte[] buffer = new byte[ 4 * 1024 ]; // 4kb is a good for network chunk

using(FileStream fs = path.OpenRead()){
   int count = 0;
   while( (count = fs.Read(buffer,0,buffer.Length)) >0 ){
      if(!response.IsClientConnected) 
      {
          // network connection broke for some reason..
          break;
      }
      response.OutputStream.Write(buffer,0,count);
      response.Flush(); // this will prevent buffering...
   }
}

您可以更改缓冲区大小，但4kb是理想的，因为较低级别的文件系统也会读取4kb块中的缓冲区。

Answer 2

Akash Kava is partly right and partly wrong. You DO NOT need to add the Content-Length header or do the flush afterward. But you DO, need to periodically flush response.OutputStream and then response. ASP.NET MVC (at least version 5) will automatically convert this into a "Transfer-Encoding: chunked" response.

byte[] buffer = new byte[ 4 * 1024 ]; // 4kb is a good for network chunk

using(FileStream fs = path.OpenRead()){
   int count = 0;
   while( (count = fs.Read(buffer,0,buffer.Length)) >0 ){
      if(!response.IsClientConnected) 
      {
          // network connection broke for some reason..
          break;
      }
      response.OutputStream.Write(buffer,0,count);
      response.OutputStream.Flush();
      response.Flush(); // this will prevent buffering...
   }
}

I tested it and it works.

FileResult缓冲到内存

2 个答案: