Clean up network/* packages, revamp online status detection

network/environment/dialing.go

@@ -0,0 +1,21 @@
+package environment
+
+import "net"
+
+var (
+	localAddrFactory func(network string) net.Addr
+)
+
+// SetLocalAddrFactory supplies the environment package with a function to get permitted local addresses for connections.
+func SetLocalAddrFactory(laf func(network string) net.Addr) {
+	if localAddrFactory == nil {
+		localAddrFactory = laf
+	}
+}
+
+func getLocalAddr(network string) net.Addr {
+	if localAddrFactory != nil {
+		return localAddrFactory(network)
+	}
+	return nil
+}