Don't crash if Yggdrasil is started with no router adapter

cmd/yggdrasil/main.go

@@ -248,10 +248,10 @@ func main() {
 	// Setup the Yggdrasil node itself. The node{} type includes a Core, so we
 	// don't need to create this manually.
 	n := node{}
-	// Now that we have a working configuration, we can now actually start
-	// Yggdrasil. This will start the router, switch, DHT node, TCP and UDP
-	// sockets, TUN/TAP adapter and multicast discovery port.
+	// Before we start the node, set the TUN/TAP to be our router adapter
 	n.core.SetRouterAdapter(&n.tuntap)
+	// Now start Yggdrasil - this starts the DHT, router, switch and other core
+	// components needed for Yggdrasil to operate
 	state, err := n.core.Start(cfg, logger)
 	if err != nil {
 		logger.Errorln("An error occurred during startup")

src/yggdrasil/core.go

@@ -220,10 +220,12 @@ func (c *Core) Start(nc *config.NodeConfig, log *log.Logger) (*config.NodeState,
 		return nil, err
 	}
 
+	if c.router.adapter != nil {
 		if err := c.router.adapter.Start(c.router.addr, c.router.subnet); err != nil {
 			c.log.Errorln("Failed to start TUN/TAP")
 			return nil, err
 		}
+	}
 
 	go c.addPeerLoop()
 
@@ -234,7 +236,9 @@ func (c *Core) Start(nc *config.NodeConfig, log *log.Logger) (*config.NodeState,
 // Stops the Yggdrasil node.
 func (c *Core) Stop() {
 	c.log.Infoln("Stopping...")
+	if c.router.adapter != nil {
 		c.router.adapter.Close()
+	}
 	c.admin.close()
 }
 

src/yggdrasil/router.go

@@ -128,8 +128,10 @@ func (r *router) init(core *Core) {
 	r.nodeinfo.setNodeInfo(r.core.config.Current.NodeInfo, r.core.config.Current.NodeInfoPrivacy)
 	r.core.config.Mutex.RUnlock()
 	r.cryptokey.init(r.core)
+	if r.adapter != nil {
 		r.adapter.Init(&r.core.config, r.core.log, send, recv, reject)
 	}
+}
 
 // Starts the mainLoop goroutine.
 func (r *router) start() error {