Maint: port forwarding refactoring (#543)

- portforward package
- portforward run loop
- Less functional arguments and cycles

internal/portforward/firewall.go

@@ -0,0 +1,32 @@
+package portforward
+
+import "context"
+
+// firewallBlockPort obtains the state port thread safely and blocks
+// it in the firewall if it is not the zero value (0).
+func (l *Loop) firewallBlockPort(ctx context.Context) {
+	port := l.state.GetPortForwarded()
+	if port == 0 {
+		return
+	}
+
+	err := l.portAllower.RemoveAllowedPort(ctx, port)
+	if err != nil {
+		l.logger.Error("cannot block previous port in firewall: " + err.Error())
+	}
+}
+
+// firewallAllowPort obtains the state port thread safely and allows
+// it in the firewall if it is not the zero value (0).
+func (l *Loop) firewallAllowPort(ctx context.Context) {
+	port := l.state.GetPortForwarded()
+	if port == 0 {
+		return
+	}
+
+	startData := l.state.GetStartData()
+	err := l.portAllower.SetAllowedPort(ctx, port, startData.Interface)
+	if err != nil {
+		l.logger.Error("cannot allow port through firewall: " + err.Error())
+	}
+}