macOS Ventura/Sonoma auto Ethernet/Wi-Fi switching

000_README.md

Auto Ethernet/Wi-Fi switching script for macOS

! CRITICAL PROBLEM ! Currently broken because ...../airport -z no longer functions and the replacement is uncertain and nonexistent for now

Installation

1. Add local.auto-switch-wifi-ethernet.zsh to /usr/local/sbin
2. Add local.auto-switch-wifi-ethernet.plist to /Library/LaunchDaemons
3. Create /usr/local/.home.wifi.ssid containing the Wi-Fi network name (SSID) to try to connect to when Ethernet is no longer internet reachable
4. Start it permanently sudo launchctl unload -w /Library/LaunchDaemons/local.auto-switch-wifi-ethernet.plist

Uninstallation

sudo launchctl unload -w /Library/LaunchDaemons/local.auto-switch-wifi-ethernet.plist
sudo rm -f /Library/LaunchDaemons/local.auto-switch-wifi-ethernet.plist \
           /usr/local/sbin/local.auto-switch-wifi-ethernet.zsh \
           /usr/local/.home.wifi.ssid
           

local.auto-switch-wifi-ethernet.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>local.auto-switch-wifi-ethernet</string>
  <key>Program</key>
  <string>/usr/local/sbin/local.auto-switch-wifi-ethernet.zsh</string>
  <key>Nice</key>
  <integer>20</integer>
  <key>KeepAlive</key>
  <true/>
  <key>StandardErrorPath</key>
  <string>/dev/null</string>
  <key>StandardOutPath</key>
  <string>/dev/null</string>
</dict>
</plist>

local.auto-switch-wifi-ethernet.zsh

#!/bin/zsh
set -euo pipefail
set -x


if [ $UID != 0 ]; then
  exec /usr/bin/sudo "$0" "$@"
fi

network_service_to_bsd_device() {
  /usr/sbin/networksetup -listnetworkserviceorder | grep -A1 ") $1$" | awk '/, Device/{gsub("[()]","");print $NF}'
}

#### Configuration
WIFI=$(network_service_to_bsd_device Wi-Fi)
DEFAULT_SSID=$(cat /usr/local/.home.wifi.ssid || { echo >&2 'Missing /usr/local/.home.wifi.ssid'; exit 1; })
#### Configuration


airport_getnetwork() {
  /usr/sbin/networksetup -getairportnetwork "$WIFI" \
    | /usr/bin/sed 's/^Current Wi-Fi Network: //'
}

find_ip() {
  local DEV=$(network_service_to_bsd_device "$1")
  echo >&2 "find_ip $DEV -> $1"
  { /sbin/ifconfig "$DEV" inet 2>/dev/null || true ; } \
    | /usr/bin/sed -E '/^[[:space:]]+inet /!d;s/[[:space:]]+inet ([0-9.]+).*/\1/;/^169\.254\./d;/^0\.0\.0\.0/d'
}

default_gateway_for_interface() {
  /usr/sbin/netstat -rn | /usr/bin/awk "/default/ && /${1//\//\/}$/{print\$2}" 
}

disassociate() {
  if ! is_associated; then # wifi is already disconnected
    return
  fi
  echo "On ethernet"
  ORIG_SSID=$(airport_getnetwork)
  echo "Disabling wifi network $WIFI"
  # TODO FIXME currently broken!
  /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -z
}

airport_power() {
  /usr/sbin/networksetup -getairportpower "$WIFI" | grep -q ': On'
}

toggle_airpower() {
  if airport_power; then
    echo "Connecting to default wifi network"
    /usr/sbin/networksetup -setairportpower "$WIFI" off
    sleep 1
    /usr/sbin/networksetup -setairportpower "$WIFI" on
    sleep 10
  else
    echo "Not connecting to wifi because it was off previously"
  fi
}

connect_to_network() {
    echo "Connecting to previous wifi network $1"
    local PASSWD=$(/usr/bin/security find-generic-password -D "AirPort network password" -wa "$1")

    for ((TRIES = 0; TRIES < 3; TRIES++)); do
      /usr/sbin/networksetup -setairportnetwork "$WIFI" "$1" "$PASSWD"
      sleep 1
      if is_associated; then
        echo >&2 'Connected OK'
        return 0
      fi
    done

    echo >&2 'Unable to connect to wifi network'
    return 1
}

associate() {
  if is_associated; then
    return
  fi
  echo "On Wi-Fi"
  if [ -n "${ORIG_SSID-}" ]; then
    connect_to_network "$ORIG_SSID" && return
  fi
  if [ -n "${DEFAULT_SSID-}" ]; then
    connect_to_network "$DEFAULT_SSID" && return
  fi
  toggle_airpower
}


is_associated() {
  ! /usr/sbin/networksetup -getairportnetwork "$WIFI" | grep -q 'You are not associated with an AirPort network.'
}

is_network_reachable() {
  if [ -z "$1" ]; then
    echo >&2 'is_network_reachable parameter error: BSD network device missing'
    return 1
  fi
  local gateway=$(default_gateway_for_interface "$1")
  [ -n "$gateway" ] || return 1
  nc -z "$gateway" 443 -b "$1" -G 2
}

is_internet_reachable() {
  if [ -z "$1" ]; then
    echo >&2 'is_internet_reachable parameter error: BSD network device missing'
    return 1
  fi
  echo >&2 "Checking network reachability for internet '$1'"
  /usr/bin/nc -z 8.8.8.8 443 -b "$1" -G 2
}

wifi_device() {
  network_service_to_bsd_device 'Wi-Fi'
}

is_internet_reachable_from_wifi() {
  is_internet_reachable $(wifi_device)
}

has_ethernet() {
  sleep 1
  local ETHS=()
  readarray -t ETHS < <(/usr/sbin/networksetup -listallnetworkservices | sed '/^\*/d;/^An asterisk/d;/^Wi-Fi/d')
  local HAS_ETH=
  local E
  for E in "${ETHS[@]}"; do
    HAS_ETH=$(find_ip "$E")
    if [ -n "$HAS_ETH" ]; then
      echo "Active ethernet device found '$E'"
      ETH="$E"
      return 0
    fi
  done
  return 1
}

while :; do
  if has_ethernet; then
    DEV=$(network_service_to_bsd_device "$ETH")
    if is_internet_reachable "$DEV"; then
      disassociate
      continue
    fi
    # TODO: handle cases where internet isn't reachable from ethernet
  else
    # TODO: handle precondition cases where association isn't desired and to prevent flapping
    associate
  fi
  sleep 2
done