wgengine/magicsock: return early, outdent in derpWriteChanOfAddr

wgengine/magicsock/magicsock.go

@@ -688,6 +688,8 @@ func (c *Conn) derpWriteChanOfAddr(addr *net.UDPAddr) chan<- derpWriteRequest {
 	if !addr.IP.Equal(derpMagicIP) {
 		return nil
 	}
+	nodeID := addr.Port
+
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	if !c.wantDerp || c.closed {
@@ -697,13 +699,18 @@ func (c *Conn) derpWriteChanOfAddr(addr *net.UDPAddr) chan<- derpWriteRequest {
 		c.logf("DERP lookup of %v with no private key; ignoring", addr)
 		return nil
 	}
-	ad, ok := c.activeDerp[addr.Port]
-	if !ok {
+
+	ad, ok := c.activeDerp[nodeID]
+	if ok {
+		*ad.lastWrite = time.Now()
+		return ad.writeCh
+	}
+
 	if c.activeDerp == nil {
 		c.activeDerp = make(map[int]activeDerp)
 		c.prevDerp = make(map[int]*syncs.WaitGroupChan)
 	}
-		derpSrv := c.derps.ServerByID(addr.Port)
+	derpSrv := c.derps.ServerByID(nodeID)
 	if derpSrv == nil || derpSrv.HostHTTPS == "" {
 		return nil
 	}
@@ -712,10 +719,10 @@ func (c *Conn) derpWriteChanOfAddr(addr *net.UDPAddr) chan<- derpWriteRequest {
 	// so it is safe to do under the mu lock.
 	dc, err := derphttp.NewClient(c.privateKey, "https://"+derpSrv.HostHTTPS+"/derp", c.logf)
 	if err != nil {
-			c.logf("derphttp.NewClient: port %d, host %q invalid? err: %v", addr.Port, derpSrv.HostHTTPS, err)
+		c.logf("derphttp.NewClient: port %d, host %q invalid? err: %v", nodeID, derpSrv.HostHTTPS, err)
 		return nil
 	}
-		dc.NotePreferred(c.myDerp == addr.Port)
+	dc.NotePreferred(c.myDerp == nodeID)
 	dc.DNSCache = dnscache.Get()
 	dc.TLSConfig = c.derpTLSConfig
 
@@ -726,23 +733,23 @@ func (c *Conn) derpWriteChanOfAddr(addr *net.UDPAddr) chan<- derpWriteRequest {
 	ad.writeCh = ch
 	ad.cancel = cancel
 	ad.lastWrite = new(time.Time)
-		c.activeDerp[addr.Port] = ad
+	c.activeDerp[nodeID] = ad
 
 	// Build a startGate for the derp reader+writer
 	// goroutines, so they don't start running until any
 	// previous generation is closed.
 	startGate := syncs.ClosedChan()
-		if prev := c.prevDerp[addr.Port]; prev != nil {
+	if prev := c.prevDerp[nodeID]; prev != nil {
 		startGate = prev.DoneChan()
 	}
 	// And register a WaitGroup(Chan) for this generation.
 	wg := syncs.NewWaitGroupChan()
 	wg.Add(2)
-		c.prevDerp[addr.Port] = wg
+	c.prevDerp[nodeID] = wg
 
 	go c.runDerpReader(ctx, addr, dc, wg, startGate)
 	go c.runDerpWriter(ctx, addr, dc, ch, wg, startGate)
-	}
+
 	*ad.lastWrite = time.Now()
 	return ad.writeCh
 }