Details
Major Description
Background: If one calls TelnetInputStream.read() in single-threaded mode (no
reader thread) and there is no data immediately available, the call blocks on
a socket read. When data starts to arrive, the stream adds all the available
bytes to its internal queue before returning the first one to the caller. To
do this, it calls __read() in a loop for as long as there are bytes available.
The __read() method returns the first byte of "user data" from the socket. If
__read() encounters a Telnet command sequence (IAC, WILL, WONT, DO, DONT,
etc.), it handles the negotiation transparently and then returns the first
byte of user data.
In most cases, this works fine, but a problem arises if a chunk of data from
the remote host ends in a Telnet command sequence. When that happens, the
TelnetInputStream.read() method hangs, even though it may have already
acquired some user data. This is because it calls __read() in a loop as long
as super.available() returns true. But if the remaining data from the socket
consists entirely of Telnet commands, __read() will process those AND THEN
BLOCK waiting for user data.
Just checking super.available() is not sufficient. We should continue the loop
only if there are bytes of USER DATA still available from the socket. Not
doing this can cause the client to wait indefinitely.