wait-for

#!/bin/sh

# Exit with error if any command fails.
set -e

TIMEOUT=30
QUIET=

USAGE="Usage: $0 [-h] [-q] [-t TIMEOUT] [-c COMMAND] HOST:PORT [HOST:PORT ..]

Wait for services to become available by scanning host/ports.

Positional arguments:
    HOST:PORT               Socket to wait for. Can be specified multiple
                            times.

Options:
    -h                      Show this help message and exit.
    -q                      Do not output any status messages.
    -t TIMEOUT              Timeout in seconds, 0 tries forever,
                            defaults to $TIMEOUT.
    -c COMMAND              Run given command with arguments after host:port is
                            available.
"

log() { if [ -z "$QUIET" ]; then echo "$@" >&2; fi; }

usage_error() { echo "$USAGE" >&2 && echo "ERROR: $@" >&2 && exit 2; }

wait_for() {
    log "Waiting for $HOST:$PORT"
    for i in `seq $TIMEOUT` ; do
        if nc -z "$HOST" "$PORT" > /dev/null 2>&1; then
            log "UP: $HOST:$PORT"
            return
        fi
        log "DOWN: $HOST:$PORT"
        sleep 1
    done
    echo "TIMEOUT: $HOST:$PORT" >&2
    exit 1
}

while getopts "hqt:c:" opt; do
    case "$opt" in
        h)
            echo "$USAGE"
            exit
            ;;
        q)
            QUIET=1
            ;;
        t)
            TIMEOUT=$OPTARG
            ;;
        c)
            CMD=$OPTARG
            ;;
        \?)
            usage_error "Invalid option: -$OPTARG"
            ;;
    esac
done

shift $(expr $OPTIND - 1)
if [ $# -eq 0 ]; then
    usage_error "No HOST:PORT provided to wait for"
fi

while [ $# -gt 0 ]; do
    HOST=$(printf "%s\n" "$1"| cut -d : -f 1)
    PORT=$(printf "%s\n" "$1"| cut -d : -f 2)
    if [ -z "$HOST" ] || [ -z "$PORT" ]; then
        usage_error "Invalid HOST:PORT \"$HOST:$PORT\""
    fi
    wait_for
    shift 1
done
if [ -n "$CMD" ]; then
    log "Will execute command $CMD"
    exec $CMD
fi