Using net.Listen to look for open ports before binding them with Gin

Signed-off-by: Andrea Tosatto <andrea.tosy@gmail.com>

Author: atosatto

main.go

@@ -4,7 +4,9 @@
 package main
 
 import (
+	"errors"
 	"flag"
+	"net"
 	"os"
 	"os/user"
 	"path/filepath"
@@ -75,6 +77,21 @@ func launchSelfLater() {
 	log.Println("Done waiting 2 secs. Now launching...")
 }
 
+// getBindPort returns the first bindable port in the given range
+func getBindPort(minPort, maxPort int) (int, error) {
+
+	for i := minPort; i < maxPort; i++ {
+		ln, _ := net.Listen("tcp", ":"+strconv.Itoa(i))
+		if ln != nil {
+			ln.Close()
+			return i, nil
+		}
+	}
+
+	return -1, errors.New("Unable to bind any port in the range [" + strconv.Itoa(minPort) + "," + strconv.Itoa(maxPort) + ")")
+
+}
+
 func main() {
 
 	flag.Parse()
@@ -215,11 +232,18 @@ func main() {
 
 			socketHandler := wsHandler().ServeHTTP
 
-			extraOriginStr := "https://create.arduino.cc, http://create.arduino.cc, https://create-dev.arduino.cc, http://create-dev.arduino.cc, http://create-staging.arduino.cc, https://create-staging.arduino.cc"
-
-			for i := 8990; i < 9001; i++ {
-				extraOriginStr = extraOriginStr + ", http://localhost:" + strconv.Itoa(i) + ", https://localhost:" + strconv.Itoa(i)
+			portPlain, err := getBindPort(8990, 9001)
+			if err != nil {
+				panic(err)
 			}
+			portSSL, err := getBindPort(portPlain+1, 9001)
+			if err != nil {
+				panic(err)
+			}
+
+			extraOriginStr := "https://create.arduino.cc, http://create.arduino.cc, https://create-dev.arduino.cc, http://create-dev.arduino.cc, http://create-staging.arduino.cc, https://create-staging.arduino.cc"
+			extraOriginStr += ", http://localhost:" + strconv.Itoa(portPlain) + ", https://localhost:" + strconv.Itoa(portPlain)
+			extraOriginStr += ", http://localhost:" + strconv.Itoa(portSSL) + ", https://localhost:" + strconv.Itoa(portSSL)
 
 			r.Use(cors.Middleware(cors.Config{
 				Origins:         *origins + ", " + extraOriginStr,
@@ -247,38 +271,23 @@ func main() {
 					return
 				}
 
-				start := 8990
-				end := 9000
-				i := start
-				for i < end {
-					i = i + 1
-					portSSL = ":" + strconv.Itoa(i)
-					if err := r.RunTLS(portSSL, filepath.Join(dest, "cert.pem"), filepath.Join(dest, "key.pem")); err != nil {
-						log.Printf("Error trying to bind to port: %v, so exiting...", err)
-						continue
-					} else {
-						ip := "0.0.0.0"
-						log.Print("Starting server and websocket (SSL) on " + ip + "" + port)
-						break
-					}
+				portStr := ":" + strconv.Itoa(portSSL)
+				if err := r.RunTLS(portStr, filepath.Join(dest, "cert.pem"), filepath.Join(dest, "key.pem")); err != nil {
+					log.Printf("Error trying to bind to port: %v, so exiting...", err)
+				} else {
+					ip := "0.0.0.0"
+					log.Print("Starting server and websocket (SSL) on " + ip + "" + port)
 				}
 			}()
 
 			go func() {
-				start := 8990
-				end := 9000
-				i := start
-				for i < end {
-					i = i + 1
-					port = ":" + strconv.Itoa(i)
-					if err := r.Run(port); err != nil {
-						log.Printf("Error trying to bind to port: %v, so exiting...", err)
-						continue
-					} else {
-						ip := "0.0.0.0"
-						log.Print("Starting server and websocket on " + ip + "" + port)
-						break
-					}
+
+				portStr := ":" + strconv.Itoa(portPlain)
+				if err := r.Run(portStr); err != nil {
+					log.Printf("Error trying to bind to port: %v, so exiting...", err)
+				} else {
+					ip := "0.0.0.0"
+					log.Print("Starting server and websocket on " + ip + "" + port)
 				}
 			}()