How to properly stream big data from MVC3 without using too much RAM?

Question

I'd like to use HttpResponse.OutputStream together with ContentResult so that I can Flush from time to time to avoid using too much RAM by .Net.

But all examples with MVC FileStreamResult, EmptyResult, FileResult, ActionResult, ContentResult show code that gets all the data into memory and passes to one of those. Also one post suggest that returning EmptyResult together with using HttpResponse.OutputStream is bad idea. How else can I do that in MVC ?

What is the right way to organize flushable output of big data (html or binary) from MVC server ?

Why is returning EmptyResult or ContentResult or FileStreamResult a bad idea ?

Answer 1

You would want to use FileStreamResult if you already had a stream to work with. A lot of times you may only have access to the file, need to build a stream and then output that to the client.

System.IO.Stream iStream = null;

// Buffer to read 10K bytes in chunk:
byte[] buffer = new Byte[10000];

// Length of the file:
int length;

// Total bytes to read:
long dataToRead;

// Identify the file to download including its path.
string filepath  = "DownloadFileName";

// Identify the file name.
string  filename  = System.IO.Path.GetFileName(filepath);

try
{
    // Open the file.
    iStream = new System.IO.FileStream(filepath, System.IO.FileMode.Open, 
                System.IO.FileAccess.Read,System.IO.FileShare.Read);


    // Total bytes to read:
    dataToRead = iStream.Length;

    Response.ContentType = "application/octet-stream";
    Response.AddHeader("Content-Disposition", "attachment; filename=" + filename);

    // Read the bytes.
    while (dataToRead > 0)
    {
        // Verify that the client is connected.
        if (Response.IsClientConnected) 
        {
            // Read the data in buffer.
            length = iStream.Read(buffer, 0, 10000);

            // Write the data to the current output stream.
            Response.OutputStream.Write(buffer, 0, length);

            // Flush the data to the HTML output.
            Response.Flush();

            buffer= new Byte[10000];
            dataToRead = dataToRead - length;
        }
        else
        {
            //prevent infinite loop if user disconnects
            dataToRead = -1;
        }
    }
}
catch (Exception ex) 
{
    // Trap the error, if any.
    Response.Write("Error : " + ex.Message);
}
finally
{
    if (iStream != null) 
    {
        //Close the file.
        iStream.Close();
    }
    Response.Close();
}

Here is the microsoft article explaining the above code.