1 files changed, 178 insertions, 0 deletions
diff --git a/debvm-waitssh b/debvm-waitssh
new file mode 100755
index 0000000..82eb14d
--- /dev/null
+++ b/debvm-waitssh
@@ -0,0 +1,178 @@
+#!/bin/sh
+# Copyright 2023 Helmut Grohne <helmut@subdivi.de>
+# SPDX-License-Identifier: MIT
+
+: <<'POD2MAN'
+=head1 NAME
+
+debvm-waitssh - Wait for a ssh server to be reachable
+
+=head1 SYNOPSIS
+
+B<debvm-waitssh> [B<-q>] [B<-t> I<timeout>] [I<hostname>:]I<port>
+
+=head1 DESCRIPTION
+
+B<debvm-waitssh> can be used to wait for a virtual machine with exposed ssh port to be reachable on that port.
+If no hostname is given, B<127.0.0.1> is assumed. No authentication is attempted by B<debvm-waitssh>, so neither
+a username nor a key have to be supplied.
+
+=head1 OPTIONS
+
+=over 8
+
+=item B<-t> I<timeout>, B<--timeout>=I<timeout>
+
+Set the maximum duration for waiting in seconds.
+Defaults to one minute.
+
+=item B<-q>, B<--quiet>
+
+Be quiet.
+Do not output a message when the timeout has been reached without success.
+
+=back
+
+=head1 EXIT VALUES
+
+=over 8
+
+=item B<0>
+
+The server is reachable.
+
+=item B<1>
+
+A timeout was reached before the server answered.
+
+=item B<2>
+
+Usage error.
+
+=back
+
+=head1 SEE ALSO
+
+    debvm-run(1)
+
+=cut
+POD2MAN
+
+set -u
+
+TOTALTIMEOUT=60
+SCANTIMEOUT=10
+SCANDELAY=1
+VERBOSITY=1
+
+nth_arg() {
+	shift "$1"
+	printf "%s" "$1"
+}
+
+die() {
+	echo "$*" >&2
+	exit 2
+}
+usage() {
+	die "usage: $0 [-q] [-t <timeout>] [<host>:]<port>"
+}
+usage_error() {
+	echo "error: $*" >&2
+	usage
+}
+
+opt_help() {
+	# shellcheck disable=SC2317 # not dead, called as "opt_$OPTARG"
+	usage
+}
+opt_quiet() {
+	VERBOSITY=0
+}
+opt_timeout() {
+	TOTALTIMEOUT=$1
+}
+
+while getopts :qt:-: OPTCHAR; do
+	case "$OPTCHAR" in
+		q)	opt_quiet		;;
+		t)	opt_timeout "$OPTARG"	;;
+		-)
+			case "$OPTARG" in
+				help|quiet)
+					"opt_$OPTARG"
+				;;
+				timeout)
+					test "$OPTIND" -gt "$#" && usage_error "missing argument for --$OPTARG"
+					"opt_$OPTARG" "$(nth_arg "$OPTIND" "$@")"
+					OPTIND=$((OPTIND+1))
+				;;
+				timeout=)
+					"opt_${OPTARG%%=*}" "${OPTARG#*=}"
+				;;
+				*)
+					usage_error "unrecognized option --$OPTARG"
+				;;
+			esac
+		;;
+		:)
+			usage_error "missing argument for -$OPTARG"
+		;;
+		'?')
+			usage_error "unrecognized option -$OPTARG"
+		;;
+		*)
+			die "internal error while parsing command options, please report a bug"
+		;;
+	esac
+done
+shift "$((OPTIND - 1))"
+
+test "$#" = 1 || usage
+
+case "$1" in
+	"")
+		usage
+	;;
+	*:*)
+		HOST=${1%:*}
+		PORT=${1##*:}
+	;;
+	*)
+		HOST=127.0.0.1
+		PORT=$1
+	;;
+esac
+
+case "$HOST" in *@*)
+	die "$0: hostname '$HOST' must not contain the '@' character. No username is required."
+;; esac
+
+# Guard against strings containing anything but digits, strings starting with
+# zero and empty strings as the port number.
+#
+# We cannot use [!0-9] because that matches on any character (or possibly
+# multi-character collation element) that sorts in between 0 and 9.
+case "$PORT" in *[!0123456789]*|0?*|""|??????*)
+	die "$0: port '$PORT' is not an integer between 1 and 65535"
+;; esac
+if test "$PORT" -lt 1 -o "$PORT" -gt 65535; then
+	die "$0: port '$PORT' is not an integer between 1 and 65535"
+fi
+
+now=$(date +%s)
+deadline=$((now + TOTALTIMEOUT))
+while test "$now" -lt "$deadline"; do
+	start=$now
+	ssh-keyscan -t rsa -T "$SCANTIMEOUT" -p "$PORT" "$HOST" >/dev/null 2>&1 && exit 0
+	now=$(date +%s)
+	if test "$((now - start))" -lt "$SCANTIMEOUT"; then
+		sleep "$SCANDELAY"
+		now=$(date +%s)
+	fi
+done
+if [ "$VERBOSITY" -ge 1 ]; then
+	echo "$0: timeout reached trying to contact $HOST:$PORT after waiting $TOTALTIMEOUT seconds." >&2
+fi
+exit 1
+