telnet: serial + monitor TCP listeners negotiate options on accept#24
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Both serial ports (8880/tty2, 8881/tty1) and the monitor (8888) were raw TCP sockets — telnet clients stayed in NVT line-buffered mode with local echo and CR/LF mangling. Add a small RFC 854 state machine that, on accept, offers WILL ECHO + WILL SGA + WILL BINARY + DO BINARY so the client drops into char-at-a-time, host-echo, 8-bit-clean mode for the serial endpoints. Inbound IAC sequences are filtered out; outbound 0xFF on the serial side is escaped as IAC IAC. The monitor uses a passive variant (no initial offers, just declines what the client offers) so the client keeps its local line editor and echo. All monitor write paths route through a CrlfWriter so bare \n renders as CRLF on the wire, as NVT requires. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Both serial ports (8880/tty2, 8881/tty1) and the monitor (8888) were raw TCP sockets — telnet clients stayed in NVT line-buffered mode with local echo and CR/LF mangling. Add a small RFC 854 state machine that, on accept, offers WILL ECHO + WILL SGA + WILL BINARY + DO BINARY so the client drops into char-at-a-time, host-echo, 8-bit-clean mode for the serial endpoints. Inbound IAC sequences are filtered out; outbound 0xFF on the serial side is escaped as IAC IAC.
The monitor uses a passive variant (no initial offers, just declines what the client offers) so the client keeps its local line editor and echo. All monitor write paths route through a CrlfWriter so bare \n renders as CRLF on the wire, as NVT requires.