2 files changed, 52 insertions, 4 deletions

diff --git a/src/config.c b/src/config.c
index 1ac9e81..7aa046d 100644
--- a/src/config.c
+++ b/src/config.c
@@ -102,6 +102,15 @@ bool fastd_config_ifname(fastd_peer_t *peer, const char *ifname) {
 	if (strchr(ifname, '/'))
 		return false;
 
+	const char *percent = strchr(ifname, '%');
+	if (percent) {
+		if (strrchr(ifname, '%') != percent)
+			return false; /* Multiple patterns */
+
+		if (percent[1] != 'n' && percent[1] != 'k')
+			return false;
+	}
+
 	char **name = peer ? &peer->ifname : &conf.ifname;
 
 	free(*name);
diff --git a/src/iface.c b/src/iface.c
index 6cad96d..e471c89 100644
--- a/src/iface.c
+++ b/src/iface.c
@@ -464,18 +464,57 @@ void fastd_iface_write(fastd_iface_t *iface, fastd_buffer_t buffer) {
 
 /** Opens a new TUN/TAP interface, optionally associated with a specific peer */
 fastd_iface_t * fastd_iface_open(fastd_peer_t *peer) {
-	fastd_iface_t *iface = fastd_new(fastd_iface_t);
-	iface->peer = peer;
-
 	const char *ifname = conf.ifname;
+	char ifnamebuf[IFNAMSIZ];
 
 	if (peer) {
 		if (peer->ifname)
 			ifname = peer->ifname;
-		else if (!fastd_config_single_iface())
+		else if (!fastd_config_single_iface() && !(ifname && strchr(ifname, '%')))
 			ifname = NULL;
 	}
 
+	const char *percent = ifname ? strchr(ifname, '%') : NULL;
+	if (percent) {
+		if (peer) {
+			char prefix[percent - ifname + 1];
+			memcpy(prefix, ifname, percent - ifname);
+			prefix[percent - ifname] = 0;
+
+			ifname = NULL;
+
+			switch (percent[1]) {
+			case 'n':
+				if (peer->name) {
+					snprintf(ifnamebuf, sizeof(ifnamebuf), "%s%s%s", prefix, peer->name, percent+2);
+					ifname = ifnamebuf;
+				}
+
+				break;
+
+			case 'k':
+			{
+				char buf[17];
+				if (conf.protocol->describe_peer(peer, buf, sizeof(buf))) {
+					snprintf(ifnamebuf, sizeof(ifnamebuf), "%s%s%s", prefix, buf, percent+2);
+					ifname = ifnamebuf;
+				}
+			}
+				break;
+
+			default:
+				exit_bug("fastd_iface_open: invalid interface pattern");
+			}
+		}
+		else {
+			pr_error("Invalid TUN/TAP device name: `%%n' and `%%k' patterns can't be used in TAP mode");
+			return NULL;
+		}
+	}
+
+	fastd_iface_t *iface = fastd_new(fastd_iface_t);
+	iface->peer = peer;
+
 	pr_debug("initializing TUN/TAP device...");
 	open_iface(iface, ifname);