#!/usr/bin/env bash
# author: joe.zheng
# version: 21.12.08

function list_nic() {
  for i in $(ls -d /sys/class/net/*); do
    if [[ "$(cat $i/operstate)" == "up" ]]; then
       if readlink $i | grep -qv virtual; then
         echo ${i##*/}
       fi
    fi
  done
}

NAME="br0"
BASE=0
COUNT=2
NIC=$(list_nic | tail -n1) # last physical network device as default
TAP_PREFIX="tap"
DELETE="n"
DRY_RUN="n"

function usage() {
  local self=`basename $0`
  local version="$(sed -n '1,4s/# version: \(.*\)/\1/p' $0)"

  cat <<EOF
Usage: $self [-b <base>] [-d <nic>] [-D] [-N <name>] [-n] [-h] [<count>]
  Create a network bridge, and then attach a physical network interface
  and the created tap devices ($TAP_PREFIX*) to it

  -b <base>:  base index of the tap devices, default: $BASE
  -d <nic>:   physical network interface, default: $NIC
  -D:         delete created bridge and detach NIC, default: $DELETE
  -n:         dry run, print out information only, default: $DRY_RUN
  -N <name>:  name of the bridge, default: $NAME
  -h:         print the usage message

  <count>:    number of the tap devices, default: $COUNT

Examples:
  # Check information before actual execution
  $self -n

  # Create bridge $NAME, attach physical NIC $NIC and $COUNT tap devices
  $self

  # Detach physical NIC $NIC and tap devices, then delete bridge $NAME
  $self -D

  # Create bridge br1, attach physical NIC $NIC and 1 tap device ${TAP_PREFIX}10
  $self -b 10 -N br1 1

Version: $version
EOF

}

while getopts ":b:d:DnN:h" opt
do
  case $opt in
    b ) BASE=$OPTARG;;
    d ) NIC=$OPTARG;;
    D ) DELETE="y";;
    n ) DRY_RUN=y;;
    N ) NAME=$OPTARG;;
    h ) usage && exit;;
    * ) usage && exit 1;;
  esac
done

shift $((OPTIND-1))

if [[ -n $1 && $1 > 0 ]]; then
  COUNT=$1
fi

if [[ $DRY_RUN == 'y' ]]; then
  for v in BASE COUNT DELETE NAME NIC TAP_PREFIX; do
    eval echo "$v: \${$v}"
  done
  exit
fi

br="$NAME"

if [[ "$(id -u)" != "0" ]]; then
  echo "run as root please, exit"
  exit 1
fi

if list_nic | grep -qv $NIC; then
  echo "the target NIC ($NIC) is not a physical device or it can't be found"
  exit 1
fi

if [[ $DELETE == "y" ]]; then
  for ((i=BASE; i<BASE+COUNT; i++)); do
    tap="$TAP_PREFIX$i"

    echo "detach $tap"
    ip link set $tap nomaster
    ip link set $tap down

    echo "delete $tap"
    ip link delete $tap
  done

  echo "detach $NIC"
  ip link set $NIC nomaster
  ip link set $NIC down

  echo "delete $br"
  ip link delete $br type bridge

  echo "bring up $NIC again"
  ip link set $NIC up
  dhclient -v $NIC

  exit # nothing to do, quit now
fi

echo "disable bridge-netfilter"
sysctl -w net.bridge.bridge-nf-call-ip6tables=0
sysctl -w net.bridge.bridge-nf-call-iptables=0
sysctl -w net.bridge.bridge-nf-call-arptables=0
sysctl -w net.bridge.bridge-nf-filter-vlan-tagged=0

echo "create bridge if necessary"
if ip link show dev $br; then
  echo "bridge $br already exist, skip"
else
  echo "create bridge $br"
  ip link add $br type bridge

  echo "attach network interface: $NIC"
  ip link set $NIC up
  ip addr flush dev $NIC
  ip link set $NIC master $br
  
  echo "bring up $br"
  ip link set dev $br up

  echo "get the IP address for $br"
  dhclient -v $br
fi

# create tap and attach to the bridge
for ((i=BASE; i<BASE+COUNT; i++)); do
  tap="$TAP_PREFIX$i"
  if ip link show dev $tap; then
    echo "tap $tap already exist, skip"
  else
    echo "create tap $tap"
    ip tuntap add $tap mode tap user $(whoami)
    ip link set dev $tap up

    echo "attach $tap to $br"
    ip link set $tap master $br
  fi
done