TelnetClient does not handle correctly binary transmissions in two places:
First in TelnetClient#connectAction() the telnet input and output streams are
wrapped in the NetASCII streams to handle net vs platform line separator
conversion which breaks the binary data. My quick solution was to simply remove
those two wrapping streams. A more general solution might be to provide access
to the unfilterer stream with methods like getUnfilteredInputStream and
getUnfilteredOutputStream or to dynamically stop the NetASCII stream from
'corrupting' the stream when a TelnetOption.BINARY option is negotiated.
Also, in TelnetInputStream#__read() there is a bug in the __receiveState
handling for the _STATE_IAC state. When a second consecutive IAC (0x255) is
received to encode the single 0x255 character, read does not return 0x255 but
instead move on to reading the next char in the stream.
The above bug report has been moved to the subtask
I'll provide patches for this.