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 -n >/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