Function StreamWriter.drain

The intended use is to write:

w.write(data) w.drain()

When the size of the transport buffer reaches the high-water limit (the protocol is paused), block until the size of the buffer is drained down to the low-water limit and the protocol is resumed. When there is nothing to wait for, continue immediately.

Calling drain() gives the opportunity for the loop to schedule the write operation and flush the buffer. It should especially be used when a possibly large amount of data is written to the transport, and the coroutine does not process the event loop between calls to write().

Prototype