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; 600 clients @ 750 msgs/sec, or 1'000 cli @ 350 msg/s

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
• socat -,raw,echo=0 openssl:127.0.0.1:1515,verify=0
• 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

the powershell client and bash client comes bundled with the server; see protips

connecting from a web browser

oh you betcha! see the webtty readme

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

if you're using firewalld, and just want to open up the high ports (not 23 and 531) then this is probably enough:

firewall-cmd --permanent --add-port={23,531,2323,1531,2424,1515,8023}/tcp
firewall-cmd --reload

but having to specify the port when connecting is lame so consider the folllowing --

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 -A INPUT -p tcp --dport 8023 -m state --state NEW -j ACCEPT  # http/ttyd
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, and also UI demystified

protips

try the following commands and hotkeys after connecting:

• /cy enables colored nicknames
• /b3 (max cowbell) beeps on every message
• /v or ctrl-n hides names and makes wordwrap more obvious; good for viewing a wall of text that somebody pasted

other surprises

• when running r0c.py it will extract a few bundled clients for your convenience (powershell and bash); look for the [SFX] sfxdir: /tmp/pe-r0c.1000 message during startup, they'll be in a clients subfolder over there

  • if you installed r0c through pip instead then the clients will be somewhere crazy like C:\Users\ed\AppData\Roaming\Python\share\doc\r0c\clients\powershell.ps1 or /home/ed/.local/share/doc/r0c/clients/powershell.ps1, good luck!