#!/bin/bash
# Copyright (C) 2017 Ian Kelling

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


# Create a network namespace. Designed for use from systemd.

[[ $EUID == 0 ]] || exec sudo -E "$BASH_SOURCE" "$@"

cd "${BASH_SOURCE%/*}"
source ../errhandle/errcatch-function
source ../errhandle/bash-trace-function
errcatch


## begin arg parsing ##
action=$1
nn=$2 # network namespace / namespace name
## end arg parsing ##

## begin sanity checking ##

install_error=false
if ! type -p ip &>/dev/null; then
    echo "please install the iproute2 package"
    install_error=true
fi
if ! type -p iptables &>/dev/null; then
    echo "please install the iptables package"
    install_error=true
fi
if $install_error; then
    exit 1
fi

##   end sanity checking ##


v0=veth0-$nn
v1=veth1-$nn
ip_base=10.173


target=/run/netns/default
if [[ ! -e $target && ! -L $target ]]; then
    mkdir -p /run/netns
    # make the default network namespace be named
    ln -s /proc/1/ns/net $target
fi


ipd() { ip -n default "$@"; }
dexec() { ip netns exec default "$@"; }

# note: this script could be easily adapted to create a
# netns instead of using the systemd created one.
# ip netns add NAME
# ip -n NAME link set dev lo up

# random note, ip netns exec creates a mount namespace and
# remaps /etc to /etc/netns/NAME.

# head -n1 is defensive. I don't know if it's possible to have more
# than one default route.
gateway_if=$(ipd route list exact 0/0 | head -n1| sed -r 's/.*\s(\S+)\s*$/\1/')
nat() { dexec iptables -t nat $1 POSTROUTING -o $gateway_if -j MASQUERADE \
              -m comment --comment "systemd network namespace nat"; }

find_network() {
    found=false
    existing=false
    ips="$(ipd addr show | awk '$1 == "inet" {print $2}')"
    for ((i=0; i <= 254; i++)); do
        network=$ip_base.$i
        if printf "%s\n" "$ips" | grep "^${network//./\\.}"; then
            existing=true
        else
            found=true
            break
        fi
    done
}

start() {

    mkdir -p /root/mount_namespaces
    if ! mountpoint /root/mount_namespaces >/dev/null; then
        mount --bind /root/mount_namespaces /root/mount_namespaces
        mount --make-private /root/mount_namespaces
    fi
    if [[ ! -e /root/mount_namespaces/$nn ]]; then
        touch /root/mount_namespaces/$nn
    fi
    if ! mountpoint /root/mount_namespaces/$nn >/dev/null; then
        unshare --mount=/root/mount_namespaces/$nn
    fi



    find_network
    if ! $found; then
        echo "$0: error: no open network found"
        exit 1
    fi

    echo 1 | dexec dd of=/proc/sys/net/ipv4/ip_forward 2>/dev/null

    _errcatch_cleanup=stop
    ip link add $v0 type veth peer name $v1
    ip link set $v0 netns default
    ipd addr add $network.1/24 dev $v0
    ipd link set $v0 up
    nat -C &>/dev/null || nat -A
    ip addr add $network.2/24 dev $v1
    ip link set $v1 up
    ip route add default via $network.1

}

stop() {
    if ipd link list $v0 &>/dev/null; then
        # this also deletes $v1 and the route we added.
        ipd link del $v0
    fi
    find_network
    if ! $existing; then
        if nat -C &>/dev/null; then nat -D; fi
    fi
}

case $action in
    start|stop)
        $action
        ;;
    *)
        echo "$0: error: unsupported action"
        exit 1
        ;;
esac