recipes-google/hosts/gbmc-hosts-gen/gbmc-hosts-gen.sh

#!/bin/bash
source /usr/share/network/lib.sh || exit

exec_over_conf_dirs() {
  local fun="$1"
  shift

  declare -A basemap=()
  local oldshopt="$(shopt -p nullglob)"
  shopt -s nullglob
  local i=0
  local dir
  local file
  for dir in "$@"; do
    for file in "$dir"/*; do
      basemap["${file##*/}$i"]="$file"
    done
    (( i+=1 ))
  done
  $oldshopt

  local key
  for key in $(printf "%s\n" "${!basemap[@]}" | sort -r); do
    "$fun" "${basemap[$key]}" || return
  done
}

gbmc_line_to_ips() {
  local ip="$1"
  [[ -z $ip ]] && return
  local -a ipbytes
  ip_to_bytes ipbytes "$ip" || return
  ip="$(ip_bytes_to_str ipbytes)" || return

  shift
  local host
  for host in "$@"; do
    ip_to_hosts["$ip"]+=" $host"
    ip_hosts["$ip $host"]=0
  done
}

gbmc_hosts_read() {
  local file="$1"

  echo "Building /etc/hosts from $file" >&2
  while read -r line; do
    gbmc_line_to_ips ${line%%#*}
  done <"$file"
}

gbmc_hosts_gen_int() {
  local -A ip_to_hosts=()
  local -A ip_hosts=()
  exec_over_conf_dirs gbmc_hosts_read /{run,etc,usr/share}/hosts.d || return

  echo '# Autogenerated, re-execute `gbmc-hosts-gen.sh` after configured in' >&$hostsfd
  echo '#   /run/hosts.d/*' >&$hostsfd
  echo '#   /etc/hosts.d/*' >&$hostsfd
  echo '#   /usr/share/hosts.d/*' >&$hostsfd
  local ip
  local host
  for ip in "${!ip_to_hosts[@]}"; do
    local line="$ip"
    for host in "${ip_to_hosts["$ip"]}"; do
      (( ip_hosts["$ip $host"] == 0 )) || continue
      ip_hosts["$ip $host"]=1
      line+=" $host"
    done
    if [[ $line != $ip ]]; then
      echo "$line" >&$hostsfd
    fi
  done
}

gbmc_hosts_gen() {
  local lockfd
  local hostsfd
  local rc=0
  exec {lockfd}<>/run/hosts && \
    flock "$lockfd" && \
    rm -f /run/.hosts && \
    exec {hostsfd}<>/run/.hosts && \
    gbmc_hosts_gen_int && \
    mv /run/.hosts /run/hosts || rc=$?
  exec {hostsfd}>&-
  exec {lockfd}>&-
  return $rc
}

gbmc_hosts_gen