修复空指针的问题，避免程序奔溃

.env

@@ -0,0 +1 @@
+CGO_ENABLED=0

Makefile

@@ -1,17 +1,22 @@
-PROJECT=socks5lb
-VERSION=`date +%Y%m%d`
-COMMIT_HASH=`git rev-parse --short HEAD`
+#https://gqlxj1987.github.io/2018/08/14/good-makefile-golang/
+include .env
+
+PROJECT=$(shell basename "$(PWD)")
+VERSION=$(shell date +%Y%m%d)
+COMMIT_HASH=$(shell git rev-parse --short HEAD)
 
 SRC=./cmd/$(PROJECT)
 BINARY=$(PROJECT)
 
-GO_ENV=CGO_ENABLED=0
 GO_FLAGS=-ldflags="-X main.version=$(VERSION) -X 'main.commit=$(COMMIT_HASH)' -X 'main.date=`date`'"
-GO=go
+GO=$(shell which go)
 
 PACKAGES=`go list ./...`
 GOFILES=`find . -name "*.go" -type f`
 
+# Make is verbose in Linux. Make it silent.
+MAKEFLAGS += --silent
+
 all: build
 
 build: cmd/$(PROJECT)

cmd/socks5lb/program.go

@@ -20,8 +20,7 @@ import "github.com/judwhite/go-svc"
 // program to run a specific version of the local package socks5lb
 type program struct {
 	Config *socks5lb.Configure
-	pool   *socks5lb.Pool
-	Server socks5lb.Server
+	Server *socks5lb.Server
 }
 
 // Init to initial the program
@@ -33,23 +32,21 @@ func (p *program) Init(env svc.Environment) (err error) {
 	for _, v := range p.Config.Backends {
 		log.Tracef("add backend %s", v.Addr)
 		backend := socks5lb.NewBackend(v.Addr, *v.CheckConfig)
-		pool.Add(backend)
+		_ = pool.Add(backend)
 	}
 
-	p.Server = socks5lb.Server{
-		Pool:   pool,
-		Config: p.Config.ServerConfig,
-	}
+	p.Server, err = socks5lb.NewServer(pool, p.Config.ServerConfig)
 
 	return
 }
 
 // Start when the program is start
 func (p *program) Start() (err error) {
+	log.Infof("start the program")
 	go func() {
-		err = p.Server.Start()
-		if err != nil {
-			log.Panic(err)
+		if err = p.Server.Start(); err != nil {
+			log.Error(err)
+			p.Server.Stop()
 		}
 	}()
 
@@ -58,5 +55,6 @@ func (p *program) Start() (err error) {
 
 // Stop when the program is stop
 func (p *program) Stop() (err error) {
+	log.Infof("stop the program")
 	return p.Server.Stop()
 }

config.go

@@ -25,6 +25,6 @@ type ServerConfig struct {
 }
 
 type Configure struct {
-	ServerConfig *ServerConfig `yaml:"server"`
-	Backends     []Backend     `yaml:"backends"`
+	ServerConfig ServerConfig `yaml:"server"`
+	Backends     []Backend    `yaml:"backends"`
 }

pool.go

@@ -20,9 +20,12 @@ import (
 type Pool struct {
 	backends map[string]*Backend
 	current  uint64
+	lock     sync.Mutex
 }
 
 func (b *Pool) Add(backend *Backend) (err error) {
+	b.lock.Lock()
+	defer b.lock.Unlock()
 	if b.backends[backend.Addr] != nil {
 		return fmt.Errorf("%v is already exists, remove it first", backend.Addr)
 	}
@@ -32,6 +35,8 @@ func (b *Pool) Add(backend *Backend) (err error) {
 }
 
 func (b *Pool) Remove(addr string) (err error) {
+	b.lock.Lock()
+	defer b.lock.Unlock()
 	delete(b.backends, addr)
 	return
 }

redirect_linux.go

@@ -63,28 +63,38 @@ func getOriginalDstAddr(conn *net.TCPConn) (addr net.Addr, c *net.TCPConn, err e
 }
 
 var (
-	socks5Clients *socks5.Client
-	clientLock    sync.Mutex
+	currentSocks5Client *socks5.Client
+	updateClientLock    sync.Mutex
 )
 
-// socks5Client to connect to a proxy server
-func (s *Server) socks5Client() (client *socks5.Client, err error) {
-	clientLock.Lock()
+// updateSocks5Client to connect to a proxy server
+func (s *Server) updateSocks5Client() (client *socks5.Client, err error) {
+	updateClientLock.Lock()
 
 	defer func() {
-		clientLock.Unlock()
-		if err != nil || client == nil {
+		if err != nil {
 			log.Error(err)
-			socks5Clients = nil
 			return
 		}
 
-		log.Infof("markup current proxy connection: %v", client.Server)
-		socks5Clients = client
+		if client != nil && currentSocks5Client != client {
+			if currentSocks5Client != nil && (currentSocks5Client.TCPConn != nil || currentSocks5Client.UDPConn != nil) {
+				log.Tracef("close pervious client before update the current socks5 client")
+				_ = currentSocks5Client.Close()
+				currentSocks5Client = nil
+			}
+
+			log.Infof("markup current socks5 proxy client %v", client.Server)
+			currentSocks5Client = client
+		}
+
+		// lock the update client
+		updateClientLock.Unlock()
 	}()
 
 	// found a available backend
-	if backend := s.Pool.Next(); backend != nil {
+	backend := s.Pool.Next()
+	if backend != nil {
 		return backend.socks5Client(0)
 	}
 
@@ -115,14 +125,18 @@ func (s *Server) ListenTProxy(addr string) (err error) {
 	defer timer.Stop()
 	go func() {
 		for ; true; <-timer.C {
-			_, err := s.socks5Client()
-			if err != nil {
+			log.Tracef("start to update current socks5 proxy client")
+			if _, err := s.updateSocks5Client(); err != nil {
 				log.Error(err)
 			}
 		}
 	}()
 
 	for {
+		if s.tproxyListener == nil {
+			return fmt.Errorf("transparent socket listenser is closed")
+		}
+
 		tproxyConn, err := s.tproxyListener.Accept()
 		if err != nil {
 			log.Error(err)
@@ -132,11 +146,11 @@ func (s *Server) ListenTProxy(addr string) (err error) {
 		go func() {
 			defer tproxyConn.Close()
 
-			if socks5Clients == nil {
+			if currentSocks5Client == nil {
 				log.Error("not found any suitable socks5 clients")
 				return
 			}
-			log.Tracef("using connected socks5 proxy client: %v", socks5Clients.Server)
+			log.Tracef("using connected socks5 proxy client: %v", currentSocks5Client.Server)
 
 			connect, ok := tproxyConn.(*tproxy.Conn)
 			if !ok {
@@ -153,7 +167,7 @@ func (s *Server) ListenTProxy(addr string) (err error) {
 			defer orgDstConn.Close()
 
 			log.Tracef("[red-tcp] %s -> %s", srcAddr, dstAddr)
-			socks5Conn, err := socks5Clients.Dial("tcp", dstAddr.String())
+			socks5Conn, err := currentSocks5Client.Dial("tcp", dstAddr.String())
 			if err != nil {
 				log.Error(err)
 			}

server.go

@@ -29,9 +29,8 @@ type Status struct {
 
 type Server struct {
 	Pool   *Pool
-	Status map[*Backend]Status
+	Config *ServerConfig
 
-	Config           *ServerConfig
 	healthCheckTimer *time.Ticker
 
 	socks5Listener net.Listener
@@ -70,8 +69,14 @@ func (s *Server) Stop() (e error) {
 	log.Debug("shutting down the server")
 	s.healthCheckTimer.Stop()
 
-	go s.socks5Listener.Close()
-	go s.tproxyListener.Close()
+	if s.socks5Listener != nil {
+		go s.socks5Listener.Close()
+	}
+
+	if s.tproxyListener != nil {
+		go s.tproxyListener.Close()
+	}
+
 	return
 }
 
@@ -98,3 +103,10 @@ func (s *Server) Transport(dst, src io.ReadWriter) (err error) {
 	log.Tracef("transport stream is finished")
 	return
 }
+
+func NewServer(pool *Pool, config ServerConfig) (*Server, error) {
+	return &Server{
+		Pool:   pool,
+		Config: &config,
+	}, nil
+}

socks5.go

@@ -25,10 +25,11 @@ func (s *Server) ListenSocks5(addr string) (err error) {
 	defer s.socks5Listener.Close()
 
 	for {
-		socks5Conn, err := s.socks5Listener.Accept()
+		var socks5Conn net.Conn
+		socks5Conn, err = s.socks5Listener.Accept()
 		if err != nil {
 			log.Error(err)
-			continue
+			return
 		}
 
 		go func() {