fix: potential race conditions with non-local err

Some of the changes do not appear to have a potential race condition,
so there it is purely a refactor,
while in others (e.g. in broker.go and in proxy/lib/snowflake.go)
we do use the same variable from multiple threads / functions.

broker/broker.go

@@ -224,7 +224,6 @@ func main() {
 	flag.BoolVar(&unsafeLogging, "unsafe-logging", false, "prevent logs from being scrubbed")
 	flag.Parse()
 
-	var err error
 	var metricsFile io.Writer
 	var logOutput io.Writer = os.Stderr
 	if unsafeLogging {
@@ -237,6 +236,7 @@ func main() {
 	log.SetFlags(log.LstdFlags | log.LUTC)
 
 	if metricsFilename != "" {
+		var err error
 		metricsFile, err = os.OpenFile(metricsFilename, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
 
 		if err != nil {
@@ -262,7 +262,7 @@ func main() {
 	}
 
 	if !disableGeoip {
-		err = ctx.metrics.LoadGeoipDatabases(geoipDatabase, geoip6Database)
+		err := ctx.metrics.LoadGeoipDatabases(geoipDatabase, geoip6Database)
 		if err != nil {
 			log.Fatal(err.Error())
 		}
@@ -313,7 +313,7 @@ func main() {
 		for {
 			signal := <-sigChan
 			log.Printf("Received signal: %s. Reloading geoip databases.", signal)
-			if err = ctx.metrics.LoadGeoipDatabases(geoipDatabase, geoip6Database); err != nil {
+			if err := ctx.metrics.LoadGeoipDatabases(geoipDatabase, geoip6Database); err != nil {
 				log.Fatalf("reload of Geo IP databases on signal %s returned error: %v", signal, err)
 			}
 		}
@@ -326,12 +326,13 @@ func main() {
 	//   --disable-tls
 	// The outputs of this block of code are the disableTLS,
 	// needHTTP01Listener, certManager, and getCertificate variables.
+	var err error
 	if acmeHostnamesCommas != "" {
 		acmeHostnames := strings.Split(acmeHostnamesCommas, ",")
 		log.Printf("ACME hostnames: %q", acmeHostnames)
 
 		var cache autocert.Cache
-		if err = os.MkdirAll(acmeCertCacheDir, 0700); err != nil {
+		if err := os.MkdirAll(acmeCertCacheDir, 0700); err != nil {
 			log.Printf("Warning: Couldn't create cache directory %q (reason: %s) so we're *not* using our certificate cache.", acmeCertCacheDir, err)
 		} else {
 			cache = autocert.DirCache(acmeCertCacheDir)

client/lib/webrtc.go

@@ -241,7 +241,7 @@ func (c *WebRTCPeer) connect(
 		}
 	case <-time.After(DataChannelTimeout):
 		c.transport.Close()
-		err = errors.New("timeout waiting for DataChannel.OnOpen")
+		err := errors.New("timeout waiting for DataChannel.OnOpen")
 		if natPolicy != nil {
 			natPolicy.Failure(actualNatType, natTypeToSend)
 		}
@@ -259,7 +259,6 @@ func (c *WebRTCPeer) preparePeerConnection(
 	config *webrtc.Configuration,
 	keepLocalAddresses bool,
 ) error {
-	var err error
 	s := webrtc.SettingEngine{}
 
 	if !keepLocalAddresses {
@@ -282,7 +281,7 @@ func (c *WebRTCPeer) preparePeerConnection(
 	vnet, _ = stdnet.NewNet()
 
 	if c.proxy != nil {
-		if err = proxy.CheckProxyProtocolSupport(c.proxy); err != nil {
+		if err := proxy.CheckProxyProtocolSupport(c.proxy); err != nil {
 			return err
 		}
 		socksClient := proxy.NewSocks5UDPClient(c.proxy)
@@ -291,6 +290,7 @@ func (c *WebRTCPeer) preparePeerConnection(
 
 	s.SetNet(vnet)
 	api := webrtc.NewAPI(webrtc.WithSettingEngine(s))
+	var err error
 	c.pc, err = api.NewPeerConnection(*config)
 	if err != nil {
 		log.Printf("NewPeerConnection ERROR: %s", err)

common/amp/armor_encoder.go

@@ -144,7 +144,7 @@ func (enc *elementEncoder) Write(p []byte) (n int, err error) {
 		if enc.chunkCounter >= bytesPerChunk {
 			enc.chunkCounter = 0
 			enc.elementCounter += 1
-			nn, err = enc.w.Write([]byte("\n"))
+			nn, err := enc.w.Write([]byte("\n"))
 			if err != nil {
 				return total, err
 			}
@@ -153,7 +153,7 @@ func (enc *elementEncoder) Write(p []byte) (n int, err error) {
 
 		if enc.elementCounter >= chunksPerElement {
 			enc.elementCounter = 0
-			nn, err = enc.w.Write([]byte("</pre>\n"))
+			nn, err := enc.w.Write([]byte("</pre>\n"))
 			if err != nil {
 				return total, err
 			}

proxy/lib/snowflake.go

@@ -504,8 +504,7 @@ func (sf *SnowflakeProxy) makePeerConnectionFromOffer(
 			pw.Close()
 		})
 		dc.OnMessage(func(msg webrtc.DataChannelMessage) {
-			var n int
+			n, err := pw.Write(msg.Data)
-			n, err = pw.Write(msg.Data)
 			if err != nil {
 				if inErr := pw.CloseWithError(err); inErr != nil {
 					log.Printf("close with error generated an error: %v", inErr)

server/server.go

@@ -189,8 +189,7 @@ func main() {
 		log.Printf("ACME hostnames: %q", acmeHostnames)
 
 		var cache autocert.Cache
-		var cacheDir string
+		cacheDir, err := getCertificateCacheDir()
-		cacheDir, err = getCertificateCacheDir()
 		if err == nil {
 			log.Printf("caching ACME certificates in directory %q", cacheDir)
 			cache = autocert.DirCache(cacheDir)
@@ -224,7 +223,7 @@ func main() {
 			addr.Port = 80
 			log.Printf("Starting HTTP-01 ACME listener")
 			var lnHTTP01 *net.TCPListener
-			lnHTTP01, err = net.ListenTCP("tcp", &addr)
+			lnHTTP01, err := net.ListenTCP("tcp", &addr)
 			if err != nil {
 				log.Printf("error opening HTTP-01 ACME listener: %s", err)
 				pt.SmethodError(bindaddr.MethodName, "HTTP-01 ACME listener: "+err.Error())