minimodembbs.sh

#!/bin/bash

########///////////////////////////////////////########
#
# This is a bash script which uses minimodem, fifos,
# cat, and netcat to serve a telnet BBS over an audio
# line. The server and the client each run a pair of
# minimodem instances which read and write to transmit
# and receive fifos.
#
# With mic/phones splitters and some USB sound cards
# a person could connect to a BBS over the audio
# of a pair of cell phones.
#
# Also, just by crossing headphone and mic jacks
# to connect two computers over soundcards for
# tests...
#
# Theoretically could work over radio but
# would add complexity and noise so probably
# not.
#
# Call this script as a server or client from within its
# own directory where only it exists.
#
# As a server:
#    $ ./minimodembbs.sh server [bbsaddress] [bbsport]
#
# As a client:
#    $ ./minimodembbs.sh client [optional: speed] [optional: squeltch]
#
# The "server" side connects to a designated telnet
# BBS and then serves it via minimodem to the client.
# The client receives it via a receiving minimodem
# and sends commands back to the server (and BBS) via
# a transmitting minimodem instance.
#
# A pair of people could set both of their copy of
# this script to "client" mode and directly chat
# that way as well.
#
# Phillip J Rhoades 2022-02-17
#
########///////////////////////////////////////########

###########################################
# Set some variables for configuration
# and check to see if we are a server
# or a client using command line arguments
###########################################

#----------------------------------------------
# Speed and squeltch. Set as needed for
# line noise conditions.
# (Speed "rtty" has no lower case)
# Can use any of the speeds/formats
# minimodem allows, (baudrate, SAME, RTTY,etc)
#----------------------------------------------
defaultspeed=100
defaultsqueltch=2.00

#----------------------------------------------
# Check if server or client and adjust things
# as needed.
#----------------------------------------------
if [ -z "$1" ]; then
    echo ""
    echo "Call this script as a server or client."
    echo ""
    echo "As a server:"
    echo "   $ ./minimodembbs.sh server [bbsaddress] [bbsport] [optional speed] [optional squeltch]"
    echo ""
    echo "As a client:"
    echo "   $ ./minimodembbs.sh client [optional speed] [optional squeltch]"
    echo ""
    echo "-->Note: If you manually set the speed, you have to manually set the squeltch."
    echo ""
    exit
fi

if [ "$1" = "server" ]; then
    if [ -z "$2" ] && [ -z "$3" ]; then
        echo ""
        echo "To serve a BBS over twin minimodems, please include"
        echo "a server address and port number of a Telnet BBS to"
        echo "connect to:"
        echo "   $ ./minimodembbs.sh server [bbsaddress] [bbsport] [optional speed] [optional squeltch]"
        echo "-->Note: If you manually set the speed, you have to manually set the squeltch."
        echo ""
        exit
    else
        #----------------------------------------------
        # Telnet address and port of BBS you are
        # connecting to over the audio channels...
        #----------------------------------------------
        bbsaddress=$2
        bbsport=$3
    fi
    if [ -z "$4" ] && [ -z "$5" ]; then
        speed=$defaultspeed
        squeltch=$defaultsqueltch
    else
        speed=$4
        squeltch=$5
    fi
    echo "Starting as Telnet BBS Over Minimodems Server"
fi

if [ "$1" = "client" ]; then
    if [ -z "$2" ] && [ -z "$3" ]; then
        speed=$defaultspeed
        squeltch=$defaultsqueltch
    else
        speed=$2
        squeltch=$3
    fi
fi

###########################################
# Trap ctrl-c for cleanup before exiting.
###########################################
trap ctrl_c INT
function ctrl_c() {

        echo "#################"
        echo "Cleaning up before exit..."
        echo "#################"

        echo "#################"
        echo "Deleting fifos..."
        rm $rpipe
        rm $tpipe

        echo "#################"
        echo "Exiting..."
        echo "#################"
        kill 0

} 2>/dev/null

###########################################
# When working as a server, we need to not
# transmit until there is a client so we
# wait for the client to say it is ready
# to connect to the BBS by listening for
# a short initial transmit from the client
###########################################
function hello_wait() {
    echo "Waiting for a blip from a connecting client"
    head -n 1 $rpipe
}

###########################################
# Make a temp fifo for
# transmitting via a first minimodem
###########################################
tpipe=$(mktemp -u)
mkfifo -m 600 "$tpipe"

###########################################
# Make a temp fifo for
# receiving via a second minimodem
###########################################
rpipe=$(mktemp -u)
mkfifo -m 600 "$rpipe"

###########################################
# Tell the user what the receive pipe
# and the transmit pipe are...
###########################################
echo "Receive  pipe: $rpipe"
echo "Transmit pipe: $tpipe"

###########################################
# Start the receive minimodem which
# seems to continue until the script
# comes to a stop.
###########################################
echo "Starting receive"
minimodem -q --print-filter -c $squeltch -r $speed | cat >$rpipe &

# Don't move forward until we hear from a client
if [ "$1" = "server" ]; then
    hello_wait
fi

###########################################
# Start the transmit minimodem which
# seems to exit after every successful
# fifo read. So, we keep restarting it
# whenever it stops...
###########################################

while true; do
    echo "(Re)starting transmit"
    minimodem -t $speed <$tpipe &
    transmitPID=$!
    wait $transmitPID
done &

###########################################
# Use netcat to open a Telnet BBS and
# connect it through the minimodems running
# here with the minimodems running on a
# different machine through the fifos
###########################################

#----------------------------------------------
# What to do if called as a server
#----------------------------------------------
if [ "$1" = "server" ]; then
    echo "Serving telnet BBS at $bbsaddress $bbsport over double minimodems"
    cat $rpipe |while true; do netcat $bbsaddress $bbsport | cat >$tpipe; hello_wait; done;
    #cat $rpipe |netcat $bbsaddress $bbsport >$tpipe
fi

#----------------------------------------------
# What to do if called as a client
#----------------------------------------------
if [ "$1" = "client" ]; then
    echo "Starting client and connecting to double minimodems BBS server"
    echo "1" >$tpipe
    cat $rpipe & cat >$tpipe
fi