Add broadcast pinging and fix node merging by shared IP

broadcast.go

@@ -0,0 +1,69 @@
+package tendrils
+
+import (
+	"context"
+	"log"
+	"net"
+	"time"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
+)
+
+func (t *Tendrils) pingBroadcast(ctx context.Context, iface net.Interface) {
+	_, broadcast := getInterfaceIPv4(iface)
+	if broadcast == nil {
+		return
+	}
+
+	t.sendBroadcastPing(broadcast, iface.Name)
+
+	ticker := time.NewTicker(30 * time.Second)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			t.sendBroadcastPing(broadcast, iface.Name)
+		}
+	}
+}
+
+func (t *Tendrils) sendBroadcastPing(broadcast net.IP, ifaceName string) {
+	conn, err := icmp.ListenPacket("ip4:icmp", "0.0.0.0")
+	if err != nil {
+		if t.DebugARP {
+			log.Printf("[broadcast] %s: failed to create icmp socket: %v", ifaceName, err)
+		}
+		return
+	}
+	defer conn.Close()
+
+	msg := icmp.Message{
+		Type: ipv4.ICMPTypeEcho,
+		Code: 0,
+		Body: &icmp.Echo{
+			ID:   1,
+			Seq:  1,
+			Data: []byte("tendrils"),
+		},
+	}
+	msgBytes, err := msg.Marshal(nil)
+	if err != nil {
+		return
+	}
+
+	_, err = conn.WriteTo(msgBytes, &net.IPAddr{IP: broadcast})
+	if err != nil {
+		if t.DebugARP {
+			log.Printf("[broadcast] %s: failed to send ping to %s: %v", ifaceName, broadcast, err)
+		}
+		return
+	}
+
+	if t.DebugARP {
+		log.Printf("[broadcast] %s: sent ping to %s", ifaceName, broadcast)
+	}
+}