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`r0c` telnet server

retr0chat, irc-like chat service for superthin clients (on PyPI)
MIT-Licensed, 2018-01-07, ed @ irc.rizon.net
windows telnet 360 noscope <- good video

see installation or grab the latest release: r0c.py

summary

imagine being stuck on ancient gear, in the middle of nowhere, on a slow connection between machines that are even more archaic than the toaster you're trying to keep from falling apart

retr0chat is the lightweight, no-dependencies, runs-anywhere solution for when life gives you lemons

tries to be irssi
zero dependencies on python 2.6, 2.7, 3.x
supports telnet, netcat, /dev/tcp, TLS clients
modem-aware; comfortable at 1200 bps
fallbacks for inhumane conditions
- linemode
- no vt100 / ansi escape codes

endorsements

the german federal office for information security does not approve

features

irc-like:

public channels with persistent history (pgup/pgdn)
private messages (/msg acidburn hey)
nick completion with Tab ↹
notifications (bell/visual) on hilights and PMs
command subset (/nick, /join, /part, /names, /topic, /me)
inline message coloring, see /help

technical:

client behavior detection (echo, colors, charset, newline)
message input with readline-like editing (arrow-left/right, home/end, backspace)
- history of sent messages (arrow-up/down)
bandwidth-conservative (push/pop lines instead of full redraws; scroll-regions)
fast enough; 1'000 clients @ 200 msgs/sec

windows clients

use putty in telnet mode
or the powershell client
or enable Telnet Client in control panel -> programs -> programs and features -> turn windows features on or off, then press WIN+R and run telnet r0c.int

putty is the best option;

the powershell client is OK and no longer spammy as of windows 10.0.15063 (win10 1703 / LTSC)
windows-telnet has a bug (since win7) where non-ascii letters occasionally render but usually dont
- this is due to a buffer overflow in telnet.exe, so r0c will apply a rate-limit to avoid it
- looks like messages larger than 512 bytes end up messing with the unicode glyphs area? or something

linux clients

most to least recommended

client	example
telnet	`telnet r0c.int`
socat	`socat -,raw,echo=0 tcp:r0c.int:531`
bash	mostly internals
netcat	`nc r0c.int 531`

you can even exec 147<>/dev/tcp/r0c.int/531;cat<&147&while IFS= read -rn1 x;do [ -z "$x" ]&&x=$'\n';printf %s "$x">&147;done (disconnect using exec 147<&-; killall cat #sorry)

tls clients

if you enable TLS with -tpt 2424 (telnet) and/or -tpn 1515 (netcat) you can connect to r0c with TLS encryption using any of the following:

telnet-ssl -zssl -zsecure -zcacert=r0c.crt r0c.int 2424
socat -,raw,echo=0 openssl:r0c.int:1515,cafile=cert.crt
stty -icanon; ncat --ssl --ssl-trustfile r0c.crt -v r0c.int 1515
stty -icanon; openssl s_client -CAfile ~/.r0c/cert.crt -nbio -connect r0c.int:1515
windows: powershell client with port +1515 (the + enables TLS)
- powershell does not verify certificate; the other clients do

installation

just run r0c.py and that's it (usually)

or install through pypi (python3 only): python3 -m pip install --user -U r0c

you can run it as a service so it autostarts on boot:

on most linux distros: systemd service (automatically does port-forwarding)
on alpine / gentoo: openrc service
on windows: nssm probably

firewall rules

skip this section if:

you are using the systemd service
or you are running as root and do not have a firewall
or you're on windows

telnet uses port 23 by default, so on the server you'll want to port-forward 23 to 2323 (and 531 to 1531 for plaintext):

iptables -A INPUT -p tcp --dport 23 -m state --state NEW -j ACCEPT
iptables -A INPUT -p tcp --dport 531 -m state --state NEW -j ACCEPT
iptables -A INPUT -p tcp --dport 2323 -m state --state NEW -j ACCEPT
iptables -A INPUT -p tcp --dport 1531 -m state --state NEW -j ACCEPT
iptables -A INPUT -p tcp --dport 2424 -m state --state NEW -j ACCEPT  # tls telnet
iptables -A INPUT -p tcp --dport 1515 -m state --state NEW -j ACCEPT  # tls netcat
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 23 -j REDIRECT --to-port 2323
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 531 -j REDIRECT --to-port 1531

(you'll have to do this on every reboot)

documentation

not really but there is a list of commands and a list of hotkeys

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r0c telnet server