private static async Task WriteFileAsync(ActionContext context, OverlappedFileStreamResult result)
{
var output = context.HttpContext.Response.Body;
var input = result.FileStream;
var readTask = _readNotStarted;
var writeTask = _writeNotStarted;
// Triple buffer so reads and writes never overlap data
var buffers = new byte[3][];
for (var i = 0; i < buffers.Length; i++)
{
buffers[i] = ArrayPool <byte> .Shared.Rent(BufferSize);
}
var cts = new CancellationTokenSource();
var step = 1;
try
{
var count = -1;
do
{
// Wait for last read to complete before reading again
count = await readTask;
// If last read wasn't the end, submit another read
if (count != 0)
{
var inputBuffer = buffers[(step % buffers.Length)];
readTask = input.ReadAsync(inputBuffer, 0, inputBuffer.Length, cts.Token);
}
// If previous read read something, write it out
if (count > 0)
{
// Wait for last write to complete before writing again
await writeTask;
var outputBuffer = buffers[((step - 1) % buffers.Length)];
writeTask = output.WriteAsync(outputBuffer, 0, count, cts.Token);
}
step++;
} while (count != 0);
// Wait for final write to complete
await writeTask;
}
finally
{
// Cancel any pending operations
cts.Cancel();
// Return the buffers
for (var i = 0; i < buffers.Length; i++)
{
ArrayPool <byte> .Shared.Return(buffers[i]);
}
// Dispose the input stream
input.Dispose();
}
}
public Task ExecuteAsync(ActionContext context, OverlappedFileStreamResult result)
{
SetHeadersAndLog(context, result);
return(WriteFileAsync(context, result));
}
