Why is my StreamResult not returning the whole files?

Question

I have to serve large files (200-800MB) to the client from my controller. I tested FileStreamResult, but this class buffered the whole file in memory. This behavior is not good enough for my project.

Further i testest the approach from here: http://support.microsoft.com/kb/812406. Concerning the memory, this looks pretty good -but the files are not completly downloaded on the client (the original file is 210222 KB, the downloaded ones are 209551 to 209776). This means there is about 0.5 MB lost (which concequently causes the files to be broken).

Has somebody an idea? Whats the best way to do this anyway? Im grateful for everything.

Just for users in the future, the link pointed to the following code:

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();
}

Update

This is my action:

    public DownloadResult TransferTest()
    {
        string fullFilePath = @"C:\ws\Test\Test\Templates\example.pdf";
        return new DownloadResult(fullFilePath);
    }

I simply call the action directly from my browser (http://xxx.xxx/Other/TransferTest).

This code works for me with files of ~200MB. Does it fail with smaller files as well? — amitfr, Apr 17 '14 at 14:05
Yes. I analyzed the problem further and it seems that there got some bytes cut off from the end. See updated answer for my calling-code. Compression is deactivated. Got any ideas? — user2482138, Apr 17 '14 at 14:13
incidentally, there is no need to create a new buffer every iteration — Marc Gravell, Apr 17 '14 at 14:25
@Marc Gravell I appreciate your comment -this is true indeed. I planned to fix it after the code works. My mistake, thanks. — user2482138, Apr 17 '14 at 14:29
It *looks* fine; have you tried adding `Response.OutputStream.Flush()`, `Response.OutputStream.Close()` ? — Marc Gravell, Apr 17 '14 at 14:36
@Marc Gravell Of couse -this is it! Sometime you just need to read the code before you copy it blind. Thanks very much! If you write the answer i can mark it as such. — user2482138, Apr 17 '14 at 14:47

score 3 · Accepted Answer · answered Apr 17 '14 at 14:57

The code basically looks sound - you are more-or-less correctly handling the return value from Read (if I was being picky, I would say check it for <=0, but this would not be an expected behavior since you probably have a lock on the file).

The only thing that occurs is: try adding a:

Response.OutputStream.Flush();

and perhaps:

Response.OutputStream.Close();

to make sure that the output stream is flushed.

Why is my StreamResult not returning the whole files?

1 Answers1