wait-for-it.sh

#!/usr/bin/env bash
# Use this script to test if a given TCP host/port are available

WAITFORIT_cmdname=${0##*/}

echoerr() { if [[ $WAITFORIT_QUIET -ne 1 ]]; then echo "$@" 1>&2; fi; }

usage() {
  cat <<USAGE >&2
Usage:
    $WAITFORIT_cmdname host:port [-s] [-t timeout] [-- command args]
    -h HOST | --host=HOST       Host or IP under test
    -p PORT | --port=PORT       TCP port under test
                                Alternatively, you specify the host and port as host:port
    -s | --strict               Only execute subcommand if the test succeeds
    -q | --quiet                Don't output any status messages
    -t TIMEOUT | --timeout=TIMEOUT
                                Timeout in seconds, zero for no timeout
    -- COMMAND ARGS             Execute command with args after the test finishes
USAGE
  exit 1
}

wait_for() {
  if [[ $WAITFORIT_TIMEOUT -gt 0 ]]; then
    echoerr "$WAITFORIT_cmdname: waiting $WAITFORIT_TIMEOUT seconds for $WAITFORIT_HOST:$WAITFORIT_PORT"
  else
    echoerr "$WAITFORIT_cmdname: waiting for $WAITFORIT_HOST:$WAITFORIT_PORT without a timeout"
  fi
  WAITFORIT_start_ts=$(date +%s)
  while :; do
    if [[ $WAITFORIT_ISBUSY -eq 1 ]]; then
      nc -z $WAITFORIT_HOST $WAITFORIT_PORT
      WAITFORIT_result=$?
    else
      (echo >/dev/tcp/$WAITFORIT_HOST/$WAITFORIT_PORT) >/dev/null 2>&1
      WAITFORIT_result=$?
    fi
    if [[ $WAITFORIT_result -eq 0 ]]; then
      WAITFORIT_end_ts=$(date +%s)
      echoerr "$WAITFORIT_cmdname: $WAITFORIT_HOST:$WAITFORIT_PORT is available after $((WAITFORIT_end_ts - WAITFORIT_start_ts)) seconds"
      break
    fi
    sleep 1
  done
  return $WAITFORIT_result
}

wait_for_wrapper() {
  # In order to support SIGINT during timeout: http://unix.stackexchange.com/a/57692
  if [[ $WAITFORIT_QUIET -eq 1 ]]; then
    timeout $WAITFORIT_BUSYTIMEFLAG $WAITFORIT_TIMEOUT $0 --quiet --child --host=$WAITFORIT_HOST --port=$WAITFORIT_PORT --timeout=$WAITFORIT_TIMEOUT &
  else
    timeout $WAITFORIT_BUSYTIMEFLAG $WAITFORIT_TIMEOUT $0 --child --host=$WAITFORIT_HOST --port=$WAITFORIT_PORT --timeout=$WAITFORIT_TIMEOUT &
  fi
  WAITFORIT_PID=$!
  trap "kill -INT -$WAITFORIT_PID" INT
  wait $WAITFORIT_PID
  WAITFORIT_RESULT=$?
  if [[ $WAITFORIT_RESULT -ne 0 ]]; then
    echoerr "$WAITFORIT_cmdname: timeout occurred after waiting $WAITFORIT_TIMEOUT seconds for $WAITFORIT_HOST:$WAITFORIT_PORT"
  fi
  return $WAITFORIT_RESULT
}

# process arguments
while [[ $# -gt 0 ]]; do
  case "$1" in
  *:*)
    WAITFORIT_hostport=(${1//:/ })
    WAITFORIT_HOST=${WAITFORIT_hostport[0]}
    WAITFORIT_PORT=${WAITFORIT_hostport[1]}
    shift 1
    ;;
  --child)
    WAITFORIT_CHILD=1
    shift 1
    ;;
  -q | --quiet)
    WAITFORIT_QUIET=1
    shift 1
    ;;
  -s | --strict)
    WAITFORIT_STRICT=1
    shift 1
    ;;
  -h)
    WAITFORIT_HOST="$2"
    if [[ $WAITFORIT_HOST == "" ]]; then break; fi
    shift 2
    ;;
  --host=*)
    WAITFORIT_HOST="${1#*=}"
    shift 1
    ;;
  -p)
    WAITFORIT_PORT="$2"
    if [[ $WAITFORIT_PORT == "" ]]; then break; fi
    shift 2
    ;;
  --port=*)
    WAITFORIT_PORT="${1#*=}"
    shift 1
    ;;
  -t)
    WAITFORIT_TIMEOUT="$2"
    if [[ $WAITFORIT_TIMEOUT == "" ]]; then break; fi
    shift 2
    ;;
  --timeout=*)
    WAITFORIT_TIMEOUT="${1#*=}"
    shift 1
    ;;
  --)
    shift
    WAITFORIT_CLI=("$@")
    break
    ;;
  --help)
    usage
    ;;
  *)
    echoerr "Unknown argument: $1"
    usage
    ;;
  esac
done

if [[ "$WAITFORIT_HOST" == "" || "$WAITFORIT_PORT" == "" ]]; then
  echoerr "Error: you need to provide a host and port to test."
  usage
fi

WAITFORIT_TIMEOUT=${WAITFORIT_TIMEOUT:-15}
WAITFORIT_STRICT=${WAITFORIT_STRICT:-0}
WAITFORIT_CHILD=${WAITFORIT_CHILD:-0}
WAITFORIT_QUIET=${WAITFORIT_QUIET:-0}

# Check to see if timeout is from busybox?
WAITFORIT_TIMEOUT_PATH=$(type -p timeout)
WAITFORIT_TIMEOUT_PATH=$(realpath $WAITFORIT_TIMEOUT_PATH 2>/dev/null || readlink -f $WAITFORIT_TIMEOUT_PATH)

WAITFORIT_BUSYTIMEFLAG=""
if [[ $WAITFORIT_TIMEOUT_PATH =~ "busybox" ]]; then
  WAITFORIT_ISBUSY=1
  # Check if busybox timeout uses -t flag
  # (recent Alpine versions don't support -t anymore)
  if timeout &>/dev/stdout | grep -q -e '-t '; then
    WAITFORIT_BUSYTIMEFLAG="-t"
  fi
else
  WAITFORIT_ISBUSY=0
fi

if [[ $WAITFORIT_CHILD -gt 0 ]]; then
  wait_for
  WAITFORIT_RESULT=$?
  exit $WAITFORIT_RESULT
else
  if [[ $WAITFORIT_TIMEOUT -gt 0 ]]; then
    wait_for_wrapper
    WAITFORIT_RESULT=$?
  else
    wait_for
    WAITFORIT_RESULT=$?
  fi
fi

if [[ $WAITFORIT_CLI != "" ]]; then
  if [[ $WAITFORIT_RESULT -ne 0 && $WAITFORIT_STRICT -eq 1 ]]; then
    echoerr "$WAITFORIT_cmdname: strict mode, refusing to execute subprocess"
    exit $WAITFORIT_RESULT
  fi
  exec "${WAITFORIT_CLI[@]}"
else
  exit $WAITFORIT_RESULT
fi