When transferring a large amount of information from a 4 letter word, especially in interactive mode (telnet or nc) over a slower network link, the connection can be closed before all of the data has reached the client. This is due to the way we handle nc non-interactive mode, by cancelling the selector key.
Instead of cancelling the selector key for 4-letter-words, we should instead flag the NIOServerCnxn to ignore detection of a close condition on that socket (CancelledKeyException, EndOfStreamException). Since the 4lw will close the connection immediately upon completion, this should be safe to do.
ZOOKEEPER-737 for more details