Work-around issues with WSL DNS resolver

dns-sync.sh

#!/bin/bash

# Based on https://gist.github.com/matthiassb/9c8162d2564777a70e3ae3cbee7d2e95

PATH=/sbin:/bin
WINSYS32=/mnt/c/Windows/System32
PS=$WINSYS32/WindowsPowerShell/v1.0/powershell.exe
CHCP=$WINSYS32/chcp.com

PIDFILE=/var/run/dns-sync.pid
CACHE_PATH=/var/cache/dns-sync

if ! [ -d "${CACHE_PATH}" ] ; then
    mkdir -p "${CACHE_PATH}" || exit 2
fi

linux_powershell() {
    if [ -z "${__oemcp}" ] ; then
        __oemcp=$(reg.exe query "HKLM\\SYSTEM\\CurrentControlSet\\Control\\Nls\\CodePage" /v OEMCP 2>&1 | sed -n 3p | tr -d '\015' | grep -o '[[:digit:]]*')
    fi
    $CHCP $__oemcp >/dev/null
    $PS "$@" | tr -d '\015'
    $CHCP 65001 >/dev/null
}

do_start () {
    touch "${CACHE_PATH}/ns.current" "${CACHE_PATH}/search.current"
    while true
    do
        UNIQUE_SEARCH=()
        UNIQUE_NS=()

        # Retrieve nameservers from via Powershell
        if linux_powershell -Command "Get-DnsClientServerAddress -AddressFamily IPv4 | Select-Object -ExpandProperty ServerAddresses" | awk '!x[$0]++' > "${CACHE_PATH}/ns.new" ; then
            if ! cmp -s "${CACHE_PATH}/ns.current" "${CACHE_PATH}/ns.new" ; then
                mapfile -t UNIQUE_NS < "${CACHE_PATH}/ns.new"

                linux_powershell -Command "Get-DnsClientGlobalSetting | Select-Object -ExpandProperty SuffixSearchList" > "${CACHE_PATH}/search.new" | awk '!s[$0]++' > "${CACHE_PATH}/search.new"
                if ! cmp -s "${CACHE_PATH}/search.current" "${CACHE_PATH}/search.new" ; then
                    mapfile -t UNIQUE_SEARCH < "${CACHE_PATH}/search.new"
                fi

                cp -f /etc/resolv.conf "${CACHE_PATH}/resolv.conf"

                if [ ${#UNIQUE_NS[@]} -gt 0 ] ; then
                    sed -i '/^nameserver.*/d' "${CACHE_PATH}/resolv.conf"
                    for i in "${UNIQUE_NS[@]}" ; do
                        echo "nameserver ${i}" >> "${CACHE_PATH}/resolv.conf"
                    done
                    mv -vf "${CACHE_PATH}/ns.new" "${CACHE_PATH}/ns.current"
                fi

                if [ ${#UNIQUE_SEARCH[@]} -gt 0 ] ; then
                    sed -i '/^search.*/d' "${CACHE_PATH}/resolv.conf"
                    echo "search ${UNIQUE_SEARCH[@]}" >> "${CACHE_PATH}/resolv.conf"
                    mv -vf "${CACHE_PATH}/search.new" "${CACHE_PATH}/search.current"
                fi

                if ! cmp -s "${CACHE_PATH}/resolv.conf" /etc/resolv.conf ; then
                    cp -f "${CACHE_PATH}/resolv.conf" /etc/resolv.conf
                fi
            fi
        fi

        sleep 30
    done
}

do_status () {
    PID=$(cat /var/run/dns-sync.pid 2>/dev/null)
    if [ "$PID" == "" ]; then
        echo "dns-sync is not running"
        return
    fi

    if ps -p $PID > /dev/null
    then
        echo "dns-sync is running"
    else
        echo "dns-sync is not running"
    fi
}

case "$1" in
start|"")
    kill $(cat "${PIDFILE}" >/dev/null 2>&1) > /dev/null  2>&1 || true
    do_start &
    echo $! > "${PIDFILE}"
    ;;
restart|reload|force-reload)
    stop && start
    ;;
stop)
    PID=$(cat "${PIDFILE}")
    if [ -r "/proc/${PID}/cmdline" ] ; then
       kill $(cat "${PIDFILE}")
       echo "dns-sync stopped"
       rm -f "${PIDFILE}"
    else
       echo "dns-sync is not running"
    fi
    ;;
status)
    do_status
    exit $?
    ;;
*)
    echo "Usage: dns-sync.sh [start|stop]" >&2
    exit 3
    ;;
esac