1#!/bin/sh
  2
  3#
  4# Waits for the given host(s) to be available before executing a given command.
  5# Tests for availability by using netcat to connect to the hosts via TCP.
  6#
  7# Usage:
  8# ./wait-for-hosts.sh [-q] [-t seconds] [host:port] [...] [-- command args...]
  9#
 10# The script accepts multiple `host:port` combinations as arguments or defined
 11# as WAIT_FOR_HOSTS environment variable, separating the `host:port`
 12# combinations via spaces.
 13#
 14# The status output can be made quiet by adding the `-q` argument or by setting
 15# the environment variable WAIT_FOR_HOSTS_QUIET to `1`.
 16#
 17# The default timeout of 10 seconds can be changed via `-t seconds` argument or
 18# by setting the WAIT_FOR_HOSTS_TIMEOUT environment variable to the desired
 19# number of seconds.
 20#
 21# The command defined after the `--` argument separator will be executed if all
 22# the given hosts are reachable.
 23#
 24# Copyright 2016, Sebastian Tschan
 25# https://blueimp.net
 26#
 27# Licensed under the MIT license:
 28# https://opensource.org/licenses/MIT
 29#
 30
 31set -e
 32
 33is_integer() {
 34  test "$1" -eq "$1" 2> /dev/null
 35}
 36
 37set_timeout() {
 38  if ! is_integer "$1"; then
 39    printf 'Error: "%s" is not a valid timeout value.\n' "$1" >&2
 40    return 1
 41  fi
 42  TIMEOUT="$1"
 43}
 44
 45connect_to_service() {
 46  nc -w 1 -z "$1" "$2"
 47}
 48
 49quiet_echo() {
 50  if [ "$QUIET" -ne 1 ]; then echo "$@" >&2; fi
 51}
 52
 53wait_for_host() {
 54  HOST="${1%:*}"
 55  PORT="${1#*:}"
 56  if ! is_integer "$PORT"; then
 57    printf 'Error: "%s" is not a valid host:port combination.\n' "$1" >&2
 58    return 1
 59  fi
 60  if [ "$QUIET" -ne 1 ]; then
 61    printf "Waiting for host: %-${PADDING}s ... " "$1" >&2
 62  fi
 63  TIME_LIMIT=$(($(date +%s)+TIMEOUT))
 64  while ! OUTPUT="$(connect_to_service "$HOST" "$PORT" 2>&1)"; do
 65    if [ "$(date +%s)" -ge "$TIME_LIMIT" ]; then
 66      quiet_echo timeout
 67      if [ -n "$OUTPUT" ]; then
 68        quiet_echo "$OUTPUT"
 69      fi
 70      return 1
 71    fi
 72    sleep 1
 73  done
 74  quiet_echo ok
 75}
 76
 77set_padding() {
 78  PADDING=0
 79  while [ $# != 0 ]; do
 80    case "$1" in
 81      -t) shift 2;;
 82      -q) break;;
 83      --) break;;
 84       *) test ${#1} -gt $PADDING && PADDING=${#1}; shift;;
 85    esac
 86  done
 87}
 88
 89QUIET=${WAIT_FOR_HOSTS_QUIET:-0}
 90set_timeout "${WAIT_FOR_HOSTS_TIMEOUT:-10}"
 91
 92if [ "$QUIET" -ne 1 ]; then
 93  # shellcheck disable=SC2086
 94  set_padding $WAIT_FOR_HOSTS "$@"
 95fi
 96
 97while [ $# != 0 ]; do
 98  case "$1" in
 99    -t) set_timeout "$2"; shift 2;;
100    -q) QUIET=1; shift;;
101    --) shift; break;;
102     *) wait_for_host "$1"; shift;;
103  esac
104done
105
106for HOST in $WAIT_FOR_HOSTS; do
107  wait_for_host "$HOST"
108done
109
110exec "$@"