Golang client绑定本地IP和端口

有时需要指定网络通信时本地使用的IP地址和端口号。

在Go语言中可通过定义 Dialer 中LocalAddr 成员实现。

Dialer结构定义如下：

// 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是接口类型，其定义如下：

// 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")
}


目前实现Addr接口的类型并且被net 库支持的类型 包括：TCPAddr、UDPAddr、IPAddr。

下面通过代码演示如何指定client 使用的IP和端口号。

例子中使用TCPAddr 类型。

client


package mainimport ("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 mainimport (
"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")}

测试

启动client,只指定端口

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


启动client，指定IP,Port

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


server输出

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


查看连接

$ 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


从测试结果看，可以成功指定IP和端口。