wait-for/wait-for

#!/usr/bin/env sh

WAITFOR_TIMEOUT=${WAITFOR_TIMEOUT:-15}
WAITFOR_QUIET=${WAITFOR_QUIET:-0}

HAS_NC=0
HAS_BASH=0

echoerr() {
  if [ "$WAITFOR_QUIET" -ne 1 ]; then printf "%s\n" "$*" 1>&2; fi
}

usage() {
  exitcode="$1"
  cat <<USAGE >&2
usage: wait-for host:port [-t timeout] [-- command args]

Synchronize services like containers and wait for readiness.

optional arguments:
  -q | --quiet                              Do not output any status messages
  -t WAITFOR_TIMEOUT | --timeout=timeout    Timeout in seconds, zero for no timeout
  -- COMMAND ARGS                           Execute command with args after the test finishes
USAGE
  exit "$exitcode"
}

wait_for() {
  for _ in $(seq "$WAITFOR_TIMEOUT"); do
    if [ $HAS_NC = 1 ]; then
      nc -w 1 -z "$WAITFOR_HOST" "$WAITFOR_PORT" >/dev/null 2>&1
    elif [ $HAS_BASH = 1 ]; then
      # shellcheck disable=SC3025
      bash -c "</dev/tcp/$WAITFOR_HOST/$WAITFOR_PORT" >/dev/null 2>&1
    fi

    result=$?
    if [ $result -eq 0 ]; then
      if [ $# -gt 0 ]; then
        exec "$@"
      fi
      exit 0
    fi
    sleep 1
  done
  echo "error: operation timed out" >&2
  exit 1
}

while [ $# -gt 0 ]; do
  case "$1" in
  *:*)
    WAITFOR_HOST=$(printf "%s\n" "$1" | cut -d : -f 1)
    WAITFOR_PORT=$(printf "%s\n" "$1" | cut -d : -f 2)
    shift 1
    ;;
  -q | --quiet)
    WAITFOR_QUIET=1
    shift 1
    ;;
  -t)
    WAITFOR_TIMEOUT="$2"
    if [ "$WAITFOR_TIMEOUT" = "" ]; then break; fi
    shift 2
    ;;
  --timeout=*)
    WAITFOR_TIMEOUT="${1#*=}"
    shift 1
    ;;
  --)
    shift
    break
    ;;
  --help)
    usage 0
    ;;
  *)
    echoerr "unknown argument: $1"
    usage 1
    ;;
  esac
done

if [ -x "$(command -v nc)" ]; then
  HAS_NC=1
fi

if [ -x "$(command -v bash)" ]; then
  HAS_BASH=1
fi

if [ $HAS_NC = 0 ] || [ $HAS_BASH = 0 ]; then
  echoerr "error: netcat or bash is required for wait-for to run"
  exit 1
fi

if [ "$WAITFOR_HOST" = "" ] || [ "$WAITFOR_PORT" = "" ]; then
  echoerr "error: you need to provide a host and port to test"
  usage 2
fi

wait_for "$@"