sauttefk / ttybus

A simple TTY multiplexer.

TTYBUS project

Copyright (c) 2010 Daniele Lacamera [e-mail]

dpipe command - copyright 2003 Renzo Davoli

Daemonization option - copyright 2020 Frank Sautter [e-mail]

OVERVIEW

The TTYBUS project is a toolkit that provides tty device virtualization, multiplexing, spoofing and sharing among unix processes. It allows users to connect their real and virtual terminals (including real serial devices) to a shared, non-reliable bus, and then to virtually any input/output stream.

LICENSE

TTYBUS comes without any warranty and it is released under the terms of the GNU/GPL v.2

IDEA

TTYBUS steals the architecture concept from VDE (Virtual Distributed Ethernet) design. The working scheme is quite simple: Users can connect their ttys together in a virtual bus, then all data sent and received from any of the devices connected to the virtual bus is echoed to all other devices.

This includes real and virtual tty devices, with the possibility to create fake devices using posix pseudo-terminals.

COMPONENTS

tty_bus

Creates a new tty_bus running on the system, at a given bus path specified with the -s option. The command creates the bus and exposes a unix socket at the given path. Once the path has been created, any device can be plugged in using the other toolkit's commands. The -d option deamonizes the process and detaches it from the terminal.

tty_plug

Connects STDIN/STDOUT of the current terminal to the tty_bus specified with the -s option. Eventually the -i option can be specified to add an init string to be passed to process stdout before it's connected to the tty_bus. The -d option deamonizes the process and detaches it from the terminal.

tty_fake

Creates a new pseudo-terminal devices connected to the tty_bus specified with the -s option. If the given path for the fake device already exists, tty_fake can be forced to replace it with the -o option. The -d option deamonizes the process and detaches it from the terminal.

tty_attach

Open a real (existing) tty and connects it to the tty_bus specified with the -s option. Eventually the -i option can be specified to add an init string to be passed to the real tty device before it's connected to the tty_bus. The -d option deamonizes the process and detaches it from the terminal.

dpipe

Taken from the VDE project, allows two unix processes to communicate each-other by attaching each process' STDOUT stream to the other one's STDIN.

Please refer to each command's help for usage notes, using the -h option .

EXAMPLES

Use case 1

Multiplexing serial input only or output only device attached to /dev/ttyS0, for use with multiple applications.

1. Create a new tty_bus called /tmp/ttyS0mux:

   tty_bus -d -s /tmp/ttyS0mux

2. Connect the real device to the bus using tty_attach:

   tty_attach -d -s /tmp/ttyS0mux /dev/ttyS0

3. Create two fake /dev/ttyS0 devices, attached to the bus:

   tty_fake -d -s /tmp/ttyS0mux /dev/ttyS0fake0

   tty_fake -d -s /tmp/ttyS0mux /dev/ttyS0fake1

4. Start your application and force it to use the new serial device for input or output

   /bin/foo /dev/ttyS0fake0 &

   /bin/bar /dev/ttyS0fake1 &

Both application will read (or write) from the same serial device.

CAUTION: All data written on each of the two fake devices will be echoed on the other one too.

Use case 2

Create fake NMEA devices from your running gpsd daemon.

1. Create the bus:

   tty_bus -s /tmp/gpsmux

2. Use dpipe, tty_plug and netcat to connect tcp socket to gpsd daemon. Send 'r' as init string to get NMEA flow from the socket:

   dpipe tty_plug -s /tmp/gpsmux -i "r" = nc -c ip.address.of.gpsd 2947

3. Create a fake gps device

   tty_fake -s /tmp/gpsmux /dev/gps0

4. Connect your legacy serial, non gpsd-compatible, nmea application to the fake device /dev/gps0

   /usr/local/games/stupid_nmea_app /dev/gps0

Use case 3:

Remote serial device via SSH tunnel. Host mars has a serial device connected on /dev/ttyUSB0, which must be accessed and used from host venus.

1. Create two tty_busses, one per machine.

   mars:$ tty_bus -s /tmp/exported_ttybus

   venus:$ tty_bus -s /tmp/remote_ttybus

2. On mars, attach the device to the local bus:

   mars:$ tty_attach -s /tmp/exported_ttybus /dev/ttyUSB0

3. On venus, prepare the fake tty device, on the same path, temporarly overriding the local /dev/ttyUSB0 device:

   venus:$ tty_fake -s /tmp/remote_ttybus -o /dev/ttyUSB0

4. Connect the two buses on the two hosts, using remote ssh command and tty_plug:

   venus:$ dpipe tty_plug -s /tmp/remote_ttybus = ssh mars tty_plug -s /tmp/exported_ttybus

From now on, the /dev/ttyUSB0 on venus is actually the device connected on mars. If it existed before being overridden, the original /dev/ttyUSB0 is restored once the tty_fake process on venus gets killed.