Improve hostname/IP default values

Default IP+hostname values were incorrect for my VPS provider. I
improved the detection, which should give correct results results for
almost any provider. Specific issues addressed:

- icanhazip.com detection was only enabled in non-interactive mode
- `hostname` is by convention a short (non-fqdn) name in Ubuntu
- `hostname --fqdn` fails if provider does not pouplate `hosts` file
- `hostname -i` fails if provider does not populate `hosts` file
- `curl` without `--fail` will someday return crazy results
  when icanhazip.com returns 500 errors or similar

setup/functions.sh

@@ -19,6 +19,34 @@ function apt_install {
 	DEBIAN_FRONTEND=noninteractive apt-get -qq -y install $PACKAGES > /dev/null;
 }
 
+function get_default_hostname {
+	set -- $(hostname --fqdn      2>/dev/null ||
+                 hostname --all-fqdns 2>/dev/null ||
+                 hostname             2>/dev/null)
+	printf '%s\n' "$1"
+}
+
+function get_default_publicip {
+	get_publicip_from_web_service || get_publicip_from_dns
+}
+
+function get_publicip_from_web_service {
+	curl --fail --silent icanhazip.com 2>/dev/null
+}
+
+function get_publicip_from_dns {
+	set -- $(hostname --ip-address       2>/dev/null) \
+	       $(hostname --all-ip-addresses 2>/dev/null)
+	while (( $# )) && is_loopback_ip "$1"; do
+		shift
+	done
+	printf '%s\n' "$1"
+}
+
+function is_loopback_ip {
+	[[ "$1" == 127.* ]]
+}
+
 function ufw_allow {
 	if [ -z "$DISABLE_FIREWALL" ]; then
 		# ufw has completely unhelpful output