setup-hostname: validate the given hostname

1 files changed, 27 insertions, 3 deletions

diff --git a/setup-hostname.in b/setup-hostname.in
index b1c2379..f97f487 100755
--- a/setup-hostname.in
+++ b/setup-hostname.in
@@ -5,9 +5,33 @@ PREFIX=
 
 . $PREFIX/lib/libalpine.sh
 
-HOST=`hostname`
-echon "Enter system hostname (short form, e.g. 'foo') [$HOST]: "
-default_read HOST `hostname`
+# http://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_host_names
+valid_hostname() {
+	# check length
+	if [ $(echo "$1" | wc -c) -gt 63 ]; then
+		echo "Hostname '$1' is too long."
+		return 1
+	fi
+	# check that it only contains valid chars
+	if ! [ -z "$(echo $1 | sed 's/[0-9a-z-]//g')" ]; then
+		echo "Hostname must only contain letters (a-z), digits (0-9) or -"
+		return 1
+	fi
+	# must not start with -
+	case "$1" in
+		-*) echo "Hostname must not start with a '-'"; return 1;;
+	esac
+	return 0
+}
+
+while true; do
+	HOST=`hostname`
+	echon "Enter system hostname (short form, e.g. 'foo') [$HOST]: "
+	default_read HOST `hostname`
+	if valid_hostname "$HOST"; then
+		break
+	fi
+done
 
 mkdir -p "$ROOT/etc"
 echo "$HOST" > "$ROOT/etc/hostname"