一个超级简单的 http Proxy ,实现本机代理，在pad 上方便的访问公司vpn内的资源

package main

import (
    "bytes"
    "fmt"
    "io"
    "log"
    "net"
    "net/url"
    "strings"
)

func main()  {
    var port string = "8888"
    li, err := net.Listen("tcp", ":"+port)
    if err != nil {
        log.Println("error listent ", err)
        return
    }
    defer li.Close()
    log.Println("开启监听端口 "+port)
    var i int
    //死循环监听
    clientData := make([] byte, 4096)
    for {
        client, err := li.Accept();
        if err != nil {
            log.Println("监听错误", err)
            break
        }
        i++
        n, err := client.Read(clientData)
        requestStrings:=string(clientData[:n])
        log.Println("client request : \n ", requestStrings)

        var method,uri, host, address string
        //取第一行
        fmt.Sscanf(string(clientData[:bytes.IndexByte(clientData, '\n')]), "%s%s", &method, &uri)
        key:=strings.Split(requestStrings,"\n")
        for _,c :=range( key) { 
            if strings.Index(c,"Host")!=-1{
                host=c[strings.Index(c,"Host:")+5 :]
                host=strings.TrimSpace(host)
            }
    
        }
        fmt.Printf("methods [%s],Host [%s]\n",method,host)

        //判断url有没有接口
        if strings.Index(uri, "http:") >0 {
            parseUrl,err:=url.Parse(uri)
            if err!= nil{
                log.Println("error",err)
            }
            address=parseUrl.Host
        } else if strings.Index(uri, ":443") >0 {           
            address = host + ":443"
        }else{
            address = host + ":80"
        }

        //获得了请求host和port，开始拨号进行tcp连接
        server, err := net.Dial("tcp", address)
        if err != nil {
            log.Println(err)
            continue
        }

        if method == "CONNECT" {
            fmt.Fprint(client, "HTTP/1.1 200 Connection established\r\n\r\n")
        } else  {
            server.Write(clientData[:n])
        }

        go io.Copy(server, client)
        go io.Copy(client, server)
    }
}