2.4.4 代理一个TCP客户端(示例补充)

2.4.4 代理一个TCP客户端

不能直接访问的目标网站：
package main

import (
	"io"
	"log"
	"net"
)

// echo is a handler function that simply echoes received data.
func echo(conn net.Conn) {
	defer conn.Close()

	// Create a buffer to store received data.
	b := make([]byte, 512)
	//代理连接上目标网站
	if _, err := conn.Write([]byte("proxy success connect website")); err != nil {
		log.Fatalln("Unable to write data")
	}
	for {
		// Receive data via conn.Read into a buffer.
		size, err := conn.Read(b[0:])
		if err != nil && err != io.EOF {
			log.Println("Unexpected error")
			break
		}

		if err == io.EOF && size == 0 {
			log.Println("Client disconnected")
			break
		}

		log.Printf("Received %d bytes: %s", size, string(b))

		// Send data via conn.Write.
		log.Println("Writing data")
		if _, err := conn.Write(b[0:size]); err != nil {
			log.Fatalln("Unable to write data")
		}
	}
}

func main() {
	// Bind to TCP port 20080 on all interfaces.
	listener, err := net.Listen("tcp", ":20000")
	if err != nil {
		log.Fatalln("Unable to bind to port")
	}
	log.Println("Listening on 0.0.0.0:20080")
	for {
		// Wait for connection. Create net.Conn on connection established.
		//等待连接
		conn, err := listener.Accept()
		log.Println("Received connection")
		if err != nil {
			log.Fatalln("Unable to accept connection")
		}
		// Handle the connection. Using goroutine for concurrency.
		//处理连接
		go echo(conn)
	}
}

代理：
package main

import (
	"io"
	"log"
	"net"
)

func handle(src net.Conn) {
	//website:127.0.0.1:80
	dst, err := net.Dial("tcp", "127.0.0.1:20000")
	if err != nil {
		log.Fatalln("Unable to connect to our unreachable host")
	}
	defer dst.Close()
	//告诉joe你已经通过代理连上了目标网站
	if _, err := src.Write([]byte("Success connect proxy")); err != nil {
		log.Fatalln("Unable to write data")
	}
	go func() {
		//把客户端流量导到目标网站
		if _, err := io.Copy(dst, src); err != nil {
			log.Fatalln(err)
		}
	}()
	//防止IO流阻塞
	if _, err := io.Copy(src, dst); err != nil {
		log.Fatalln(err)
	}

}

func main() {
	listener, err := net.Listen("tcp", ":30000")
	if err != nil {
		log.Fatalln("Unable to bind port")
	}
	for {
		conn, err := listener.Accept()
		if err != nil {
			log.Fatalln("Unable to accept connection")
		}
		go handle(conn)
	}
}

客户端：
package main

import (
	"bufio"
	"fmt"
	"log"
	"net"
	"os"
)

func main() {
	// Connect to the server on TCP port 20080.
	conn, err := net.Dial("tcp", "127.0.0.1:30000")
	if err != nil {
		log.Fatalln("Unable to connect to the server")
	}
	defer conn.Close()

	// Create a scanner to read input from the user.
	scanner := bufio.NewScanner(os.Stdin)

	// Create a goroutine to read and display server responses.
	go func() {
		for {
			// Read server response.
			response := make([]byte, 512)
			size, err := conn.Read(response)
			if err != nil {
				log.Fatalln("Error reading from server:", err)
				return
			}
			fmt.Printf("imformation: %s\n", string(response[:size]))
		}
	}()

	// Read user input and send it to the server.
	for {
		fmt.Print("Enter text to send to the server: \n")
		scanner.Scan()
		text := scanner.Text()

		// Send user input to the server.
		_, err := conn.Write([]byte(text))
		if err != nil {
			log.Fatalln("Error writing to server:", err)
			return
		}
	}
}

效果：

客户端能够收到来自代理的信息和目标网站的信息

输入aaaaa能够收到来自目标网站的回显效果，说明示例基本上完成了流量转发的功能，这里只是一个简单的示例，大家可以在这个基础上进行扩充。