一个简单的tcp代理(golang实现）

最近需要在生产环境中调试一个http的问题，但是网管说不能安装抓包工具......

想到的一种替代方案是，增加个反向代理，然后把所有的request和response打印一下即可

1. nginx/haproxy来做反向代理，肯定可行，但是我配置的不太熟练

2. 自己写个简单的即可，正好golang写这类程序很快，所以就花了一会儿重新熟悉下go的语法（有阵子没看忘掉了......）然后写了个

主要的思路就是接收客户端的request,然后把里面的Host header改成真正的服务器的Host,然后转发，并把接收到的response回发个客户端即可

下面是全部的代码，用法很简单 ./tcpproxy 127.0.0.1 1080 www.baidu.com:80

// TcpProxy project main.go
package main

import (
    "fmt"
    "net"
    "os"
    "regexp"
    "strconv"
)

func main() {
    if len(os.Args) < 4 {
        fmt.Println("missing message!")
        return
    }
    ip := os.Args[1]
    port, err := strconv.Atoi(os.Args[2])
    if err != nil {
        fmt.Println("error happened ,exit")
        return
    }
    addr := os.Args[3]
    host := "Host: " + addr

    Service(ip, port, addr, host)
}

func Service(ip string, port int, dstaddr string, dsthost string) {
    // listen and accept
    listen, err := net.ListenTCP("tcp", &net.TCPAddr{net.ParseIP(ip), port, ""})
    if err != nil {
        fmt.Println("listen error: ", err.Error())
        return
    }
    fmt.Println("init done...")

    for {
        client, err := listen.AcceptTCP()
        if err != nil {
            fmt.Println("accept error: ", err.Error())
            continue
        }
        go Channal(client, dstaddr, dsthost)
    }
}

func Channal(client *net.TCPConn, addr string, rhost string) {

    tcpAddr, _ := net.ResolveTCPAddr("tcp4", addr)
    conn, err := net.DialTCP("tcp", nil, tcpAddr)
    if err != nil {
        fmt.Println("connection error: ", err.Error())
        client.Close()
        return
    }

    go ReadRequest(client, conn, rhost)
    ReadResponse(conn, client)
}

func ReadRequest(lconn *net.TCPConn, rconn *net.TCPConn, dsthost string) {
    for {
        buf := make([]byte, 10240)
        n, err := lconn.Read(buf)
        if err != nil {
            break
        }

        mesg := changeHost(string(buf[:n]), dsthost)
        // print request
        fmt.Println(mesg)
        rconn.Write([]byte(mesg))
    }
    lconn.Close()
}

func ReadResponse(lconn *net.TCPConn, rconn *net.TCPConn) {
    for {
        buf := make([]byte, 10240)
        n, err := lconn.Read(buf)
        if err != nil {
            break
        }

        fmt.Println(string(buf[:n]))
        rconn.Write(buf[:n])
    }
    lconn.Close()
}

func changeHost(request string, newhost string) string {
    reg := regexp.MustCompile(`Host[^\r\n]+`)
    return reg.ReplaceAllString(request, newhost)
}