mm-connect-helper

#!/bin/sh -efux

# This file works only with IPv4. The variables in capitals are the parameters
# you can adjust to your needs

# The name of the modem network interface as shown in `ip a`
INTERFACE=wwp0s20f0u3i12

# The access point address. This is the same value as the one you typically
# have in the internet settings of your mobile phone.
#
# Some common values are
# Altel KZ: internet, internet.altel.kz
# internet.tele2.kz
# internet.beeline.kz
# APN=internet.altel.kz
# APN=halebop.telia.se
# APN=data.tre.se
# APN=online.telia.se
# APN=internet.telenor.se
APN=services.telenor.se
# APN=internet.beeline.kz
# APN=internet.beeline.ru

# File in /etc/systemd/network/ to save networkd config to
NETWORKD_CONF=30-mobile.network

# Metric for the routes set up through this interface. Can be useful to set
# priorities for network interfaces when multiple of them are online and are
# connected to internet
METRIC=30

# Hardcoding the modem id is not good, because it may change (often happens
# if you suspend/hibernate your computer). The command we do here is just a
# smarter version of
#
#   modemId=$(mmcli --list-modems | grep -oP 'Modem/\d+' | sed 's:Modem/::')
#
# It continuosly reads the output of mmcli --monitor-modems, and takes the
# first modem from there.
echo "Waiting for any modems to come online…"
modemId=$(
  (mmcli --monitor-modems &) |
    while true; do
      read l
      if m=$(echo "$l" | grep -oP 'Modem/\d+'); then
        echo "$m" | sed 's:Modem/::'
        exit # Subshell exit
      fi
    done
)

print_help() {
    cat << EOF
mm-connect-helper <command>|--help

This program is a wrapper around ModemManager's mmcli that helps connect to
internet through a 4G modem in settings where network is managed through
sysetmd-networkd (we reimplement some of NetworkManager functionality, but only
in a limited way). See Archwiki [1] for more info.

Available commands:

  status -- print the status of the modem
  connect -- connect and obtain IP address (this has the same effect as doing
    connect-only and ip)
  disconnect -- disconnect
  connect-only -- connect without obtaining the IP address
  ip -- obtain IP address

[1]: <https://wiki.archlinux.org/title/Mobile_broadband_modem>

Common errors:
  libmbim.Error.Status.ServiceNotActivated -- you might be using wrong AP settings
EOF
}

connect() {
    mmcli -m "$modemId" --simple-connect="apn=$APN"
    # The following is optional, it allows checking signal level with
    # 'mmcli -m 0 --signal-get'
    mmcli -m "$modemId" --signal-setup=5
}


disconnect() {
    mmcli -m "$modemId" --simple-disconnect
}


status() {
    mmcli -m "$modemId" --output-keyvalue | grep 'modem.generic.state' | sed 's/.*: //'
}


# Sets the ip address specified by the ModemManager
ip() {
    # FIXME: Looks like sometimes the Bearer id and Modem id do not match. How
    # do I get the correct bearer id for this command?
    body=$(mmcli -b "$modemId")

    field() {
        field="$1"
        echo "$body" | grep "$field:" | sed "s/.*$field: //"
    }

    address=$(field address)
    prefix=$(field prefix)
    gateway=$(field gateway)
    dns=$(for i in $(field dns | sed 's:, : :'); do
        echo "DNS=$i"
    done)

    (
        cat <<EOF
[Match]
Name=$INTERFACE

[Network]
IPv6LinkLocalAddressGenerationMode=none
IPv6AcceptRA=false
$dns

[Address]
Address=$address/24
RouteMetric=$METRIC

[Route]
Gateway=$gateway
Metric=$METRIC
EOF
    ) | sudo tee /etc/systemd/network/$NETWORKD_CONF
    sudo systemctl restart systemd-networkd.service
}


remove_ip() {
    sudo ip addr flush dev "$INTERFACE"
}


if [ "$#" -lt 1 ]; then
    print_help
    exit 0
fi

case "$1" in
    status)
        status
        ;;
    connect)
        connect
        ip
        ;;
    disconnect)
        disconnect
        remove_ip
        ;;
    connect-only)
        connect
        ;;
    ip)
        ip
        ;;
    --help|-h)
        print_help
        ;;
    *)
        echo "Can't recognize the parameters"
        print_help
        ;;
esac