Twisted - howto transport megabytes?

[Ed Young]

I am exploring Twisted for use as the basis for an 
application to application data transporter (queueing).

When receiving large messages (multiple megabytes), I can
use the dataReceived method to get the messages piecemeal.
Since file writes can be blocking, how can I write the
received pieces to a file in a non-blocking fashion?

When sending large messages (multiple megabytes), well,
I haven't figured that out yet.  Does the transport
method accept a filehandle from which it will feed as
it needs to?

The Twisted documentation is twisting my mind <sick_grin>.
All hints appreciated...