Tools for masking/spoofing/proxying DNS

dnsmasq.conf

#dnsmasq config, for a complete example, see:
#  http://oss.segetech.com/intra/srv/dnsmasq.conf

#log all dns queries
log-queries

#dont use host's hosts file
no-hosts
addn-hosts=./etc/hosts

#dont use host's nameservers
no-resolv
servers-file=./etc/servers

util.sh

#!/bin/bash -eux

main(){
    (
        cd $(script_dir)
        cmd="$1"
        [[ $cmd == kill ]] && cmd="kill_dnsmasq"
        shift
        $cmd "$@"
    )
}

update_hosts(){
    mkdir -p etc
    (
        host_alias example.com dq1dnt4af4eyy.cloudfront.net
    ) > etc/hosts
}

run(){
    if [[ ${1:-} == "background" ]]; then
        cmd=start_dnsmasq
        shift
    else
        cmd=start_dnsmasq_foreground
    fi
    $cmd "$@"
}

kill_dnsmasq(){
    stop_dnsmasq
}

start(){
    update_hosts
    update_servers
    if [[ ${1:-} == "background" ]]; then
        run "$@" &&
            use_local_dns
    else
        use_local_dns
        trap 'restore_dns' EXIT
        run "$@"
    fi
}

stop(){
    kill
    restore_dns
}

reload(){
    reload_dnsmasq
}

#############################
## Begin utility functions ##
#############################

ips_to_host(){
    # for each line in stdin, format as an etc/hosts entry for arg1
    # This simulates multiple A records
    local host="$1"
    awk -v host="$host" '{printf("%-16s %s\n",$0,host)}'
}

hostname_to_ips(){
    local host="$1"
    dig +short "$host"
}

host_alias(){
    local src="$1"
    local dst="$2"
    hostname_to_ips $dst | ips_to_host $src
}

start_dnsmasq(){
    sudo /usr/local/sbin/dnsmasq --conf-file=dnsmasq.conf --pid-file="$(get_pid_file)" "$@"
}

start_dnsmasq_foreground(){
    # In dnsmasq -d is "no-daemon" mode which is backwards from many other apps
    start_dnsmasq -d
    # This is the production-ready way, but it doesn't respond to SIGINT
    # start_dnsmasq --keep-in-foreground
}

signal_dnsmasq(){
    local msg=""
    if [[ -f $pid_file ]]; then
        local pid="$(cat $pid_file)"
        if ps -p $(cat $pid_file) >/dev/null; then
            sudo /bin/kill "$@" $(cat $pid_file)
        else
            msg="The dnsmasq pid ($pid) is not running."
        fi
    else
        msg="The dnsmasq pid file ($pid_file) is not present."
    fi
    if [[ -n $msg ]]; then
        echo "$msg"
        exit 255;
    fi
}

stop_dnsmasq(){
    signal_dnsmasq -TERM
}

reload_dnsmasq(){
    signal_dnsmasq -HUP
}

get_networksetup_device(){
    networksetup -listallnetworkservices | \
        grep "$(
            route -n get ${1:-8.8.8.8} | \
                awk '$1=="interface:"{
                         iface=$2
                     }
                     END{
                         if(iface=="en0"){iface="Wi-Fi"}
                         print iface
                     }'
        )"
}

uniq_ips(){
    echo $(grep -oE "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b" | sort | uniq)
}

set_dns(){
    networksetup -setdnsservers $(get_networksetup_device) "$@"
}

clear_dns(){
    set_dns Empty
}

current_resolv(){
    grep nameserver /etc/resolv.conf
}

update_servers(){
    local servers_file="$(get_servers_file)"
    current_resolv | uniq_ips | for ip in $(cat); do echo "server=$ip"; done > $servers_file
}

use_local_dns(){
    current_resolv | uniq_ips > etc/resolv.ips.bak
    set_dns 127.0.0.1
}

restore_dns(){
    clear_dns
    current_resolv | uniq_ips > etc/resolv.ips.tmp
    if ! diff etc/resolv.ips.{bak,tmp} >/dev/null; then
        set_dns $(cat etc/resolv.ips.bak)
    fi
}

get_pid_file(){
    #bash -c "$(sed -n 's/pid-file/pid_file/; /pid_file/p;' < dnsmasq.conf);"' echo $pid_file'
    echo "$PWD/etc/dnsmasq.pid"
}

get_servers_file(){
    bash -c "$(sed -n 's/servers-file/servers_file/; /servers_file/p;' < dnsmasq.conf);"' echo $servers_file'
}

script_dir(){
    echo "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
}

################
## Always run ##
################

pid_file="$(get_pid_file)"

main "$@"