Golang client綁定本地IP和端口

有時須要指定網絡通訊時本地使用的IP地址和端口號。

在Go語言中可經過定義 Dialer 中LocalAddr 成員實現。 Dialer結構定義以下：

// A Dialer contains options for connecting to an address.
//
// The zero value for each field is equivalent to dialing
// without that option. Dialing with the zero value of Dialer
// is therefore equivalent to just calling the Dial function.
type Dialer struct {
    ...

	// LocalAddr is the local address to use when dialing an
	// address. The address must be of a compatible type for the
	// network being dialed.
	// If nil, a local address is automatically chosen.
	LocalAddr Addr
}

Addr是接口類型，其定義以下：

// Addr represents a network end point address.
//
// The two methods Network and String conventionally return strings
// that can be passed as the arguments to Dial, but the exact form
// and meaning of the strings is up to the implementation.
type Addr interface {
	Network() string // name of the network (for example, "tcp", "udp")
	String() string  // string form of address (for example, "192.0.2.1:25", "[2001:db8::1]:80")
}

目前實現Addr接口的類型而且被net 庫支持的類型 包括：TCPAddr、UDPAddr、IPAddr。

下面經過代碼演示如何指定client 使用的IP和端口號。

例子中使用TCPAddr 類型。

client

package main


import (

	"bufio"
	"fmt"
	"net"
	"os"
	"time"
)


func DialCustom(network, address string, timeout time.Duration, localIP []byte, localPort int)(net.Conn,error) {
	netAddr := &net.TCPAddr{Port:localPort}

	if len(localIP) != 0 {
		netAddr.IP = localIP
	}

	fmt.Println("netAddr:", netAddr)

	d := net.Dialer{Timeout: timeout, LocalAddr: netAddr}
	return d.Dial(network, address)
}


func main() {

	serverAddr := "172.20.22.160:8080"

	// 172.28.0.180
	//localIP := []byte{0xAC, 0x1C, 0, 0xB4}  // 指定IP
	localIP := []byte{} //  any IP，不指定IP
	localPort := 9001   // 指定端口
	conn, err := DialCustom("tcp", serverAddr, time.Second*10, localIP,localPort)
	if err != nil {
		fmt.Println("dial failed:", err)
		os.Exit(1)
	}
	defer conn.Close()


	buffer := make([]byte, 512)
	reader := bufio.NewReader(conn)

	n, err2 := reader.Read(buffer)
	if err2 != nil {
		fmt.Println("Read failed:", err2)
		return
	}

	fmt.Println("count:", n, "msg:", string(buffer))

	select{}	
}

server

package main

import (
	"fmt"
	"net"
	"log"
)

func main() {

	addr := "0.0.0.0:8080"

	tcpAddr, err := net.ResolveTCPAddr("tcp",addr)

	if err != nil {
		log.Fatalf("net.ResovleTCPAddr fail:%s", addr)
	}

	listener, err := net.ListenTCP("tcp", tcpAddr)
	if err != nil {
		log.Fatalf("listen %s fail: %s", addr, err)
	} else {
	
		log.Println("rpc listening", addr)
	}


	for {
		conn, err := listener.Accept()
		if err != nil {
			log.Println("listener.Accept error:", err)
			continue
		}
	
		go handleConnection(conn)
	
	}

}


func handleConnection(conn net.Conn) {

	//defer conn.Close()

	var buffer []byte = []byte("You are welcome. I'm server.")

	n, err := conn.Write(buffer)

	if err != nil {
	
		fmt.Println("Write error:", err)
	}
	fmt.Println("send:", n)

	fmt.Println("connetion end")

}

測試

啓動client,只指定端口

$ ./client 
netAddr: :9001
count: 28 msg: You are welcome. I'm server.

啓動client，指定IP,Port

$ ./client
netAddr: 172.28.172.180:9001
count: 28 msg: You are welcome. I'm server

server輸出

./sever
2018/06/19 18:15:41 rpc listening 0.0.0.0:8080
send: 28
connetion end

查看鏈接

$ netstat -anp | grep 8080
tcp        0      0 :::8080                     :::*                        LISTEN      27328/./server      
tcp        0      0 ::ffff:172.20.22.160:8080   ::ffff:172.28.0.180:9001  ESTABLISHED 27328/./server

從測試結果看，能夠成功指定IP和端口。