Add --listeners option.

README.md

@@ -50,6 +50,8 @@ Usage of ./go-mmproxy:
     	Path to a file that contains allowed subnets of the proxy servers
   -l string
     	Adress the proxy listens on (default "0.0.0.0:8443")
+  -listeners int
+    	Number of listener sockets that will be opened for the listen address (default 1)
   -mark int
     	The mark that will be set on outbound packets
   -v int
@@ -57,6 +59,7 @@ Usage of ./go-mmproxy:
     	1 - log errors occuring in individual connections
     	2 - log all state changes of individual connections
 
+
 ```
 
 Example invocation:

main.go

@@ -7,6 +7,7 @@ package main
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"encoding/binary"
 	"flag"
 	"fmt"
@@ -26,6 +27,7 @@ var targetAddr6 string
 var allowedSubnetsPath string
 var mark int
 var verbose int
+var listeners int
 
 var allowedSubnets []*net.IPNet
 var logger *zap.Logger
@@ -40,6 +42,7 @@ func init() {
 	flag.IntVar(&verbose, "v", 0, `0 - no logging of individual connections
 1 - log errors occuring in individual connections
 2 - log all state changes of individual connections`)
+	flag.IntVar(&listeners, "listeners", 1, "Number of listener sockets that will be opened for the listen address")
 }
 
 func readRemoteAddrPROXYv2(conn net.Conn, ctrlBuf []byte) (net.Addr, net.Addr, []byte, error) {
@@ -233,9 +236,9 @@ func checkOriginAllowed(conn net.Conn) bool {
 	return false
 }
 
-func handleConnection(conn net.Conn) {
+func handleConnection(conn net.Conn, listenLog *zap.Logger) {
 	defer conn.Close()
-	connLog := logger.With(zap.String("remoteAddr", conn.RemoteAddr().String()),
+	connLog := listenLog.With(zap.String("remoteAddr", conn.RemoteAddr().String()),
 		zap.String("localAddr", conn.LocalAddr().String()))
 
 	if !checkOriginAllowed(conn) {
@@ -309,6 +312,43 @@ func handleConnection(conn net.Conn) {
 	}
 }
 
+func listen(listenerNum int, errors chan<- error) {
+	listenLog := logger.With(zap.Int("listenerNum", listenerNum))
+
+	listenConfig := net.ListenConfig{}
+	if listeners > 1 {
+		listenConfig.Control = func(network, address string, c syscall.RawConn) error {
+			return c.Control(func(fd uintptr) {
+				soReusePort := 15
+				if err := syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, soReusePort, 1); err != nil {
+					listenLog.Warn("failed to set SO_REUSEPORT - only one listener setup will succeed")
+				}
+			})
+		}
+	}
+
+	ctx := context.Background()
+	ln, err := listenConfig.Listen(ctx, "tcp", listenAddr)
+	if err != nil {
+		listenLog.Error("failed to bind listener", zap.String("listenAddr", listenAddr), zap.Error(err))
+		errors <- err
+		return
+	}
+
+	listenLog.Info("listening", zap.String("listenAddr", listenAddr))
+
+	for {
+		conn, err := ln.Accept()
+		if err != nil {
+			listenLog.Error("failed to accept new connection", zap.Error(err))
+			errors <- err
+			return
+		}
+
+		go handleConnection(conn, listenLog)
+	}
+}
+
 func loadAllowedSubnets() error {
 	file, err := os.Open(allowedSubnetsPath)
 	if err != nil {
@@ -345,29 +385,26 @@ func initLogger() error {
 
 func main() {
 	flag.Parse()
-
 	if err := initLogger(); err != nil {
 		log.Fatalf("Failed to initialize logging: %s", err.Error())
 	}
 	defer logger.Sync()
 
+	if listeners <= 0 {
+		logger.Fatal("--listeners has to be >= 1")
+	}
+
 	if allowedSubnetsPath != "" {
 		if err := loadAllowedSubnets(); err != nil {
 			logger.Fatal("failed to load allowed subnets file", zap.String("path", allowedSubnetsPath), zap.Error(err))
 		}
 	}
 
-	ln, err := net.Listen("tcp", listenAddr)
-	if err != nil {
-		logger.Fatal("failed to bind listener", zap.String("listenAddr", listenAddr), zap.Error(err))
+	listenErrors := make(chan error, listeners)
+	for i := 0; i < listeners; i++ {
+		go listen(i, listenErrors)
 	}
-
-	for {
-		conn, err := ln.Accept()
-		if err != nil {
-			logger.Fatal("failed to accept new connection", zap.Error(err))
-		}
-
-		go handleConnection(conn)
+	for i := 0; i < listeners; i++ {
+		<-listenErrors
 	}
 }