Check router connection hijacking (captive portal)

check-hijacking.sh

#!/usr/bin/env zsh
# adapted from Alterstep dnscrypt-proxy OSX client

try_resolution() {
  exec alarmer 5 dig +tries=2 +time=3 +short github.com | egrep '^192[.]30[.]'  > /dev/null 2>&1
}

try_http_query() {
  exec alarmer 5 curl -L --max-redirs 5 -4 -m 5 --connect-timeout 5 -s \
    http://icanhazip.com/ 2>/dev/null | \
  fgrep -c '.' > /dev/null 2>&1
}

try_everything() {
  try_resolution &
  resolution_pid=$!
  try_http_query &
  http_query_pid=$!
  wait $resolution_pid
  resolution_ret=$?
  if [ $resolution_ret != 0 ]; then
    return 1
  fi
  wait $http_query_pid
  http_query_ret=$?
  [ $resolution_ret = 0 -a $http_query_ret = 0 ]
}

try_everything_with_retries() {
  try_everything || try_everything
}

try_everything_with_retries