package mainimport ("bytes""fmt""io""log""net""net/url""strings"
)func main() {// tcp 连接，监听 8080 端口l, err := net.Listen("tcp", ":8080")if err != nil {log.Panic(err)}// 死循环，每当遇到连接时，调用 handlefor {client, err := l.Accept()if err != nil {log.Panic(err)}go handle(client)}
}func handle(client net.Conn) {if client == nil {return}defer client.Close()log.Printf("remote addr: %v\n", client.RemoteAddr())// 用来存放客户端数据的缓冲区var b [1024]byte//从客户端获取数据n, err := client.Read(b[:])if err != nil {log.Println(err)return}var method, URL, address string// 从客户端数据读入 method，urlfmt.Sscanf(string(b[:bytes.IndexByte(b[:], '\n')]), "%s%s", &method, &URL)hostPortURL, err := url.Parse(URL)if err != nil {log.Println(err)return}// 如果方法是 CONNECT，则为 https 协议if method == "CONNECT" {address = hostPortURL.Scheme + ":" + hostPortURL.Opaque} else { //否则为 http 协议address = hostPortURL.Host// 如果 host 不带端口，则默认为 80if strings.Index(hostPortURL.Host, ":") == -1 { //host 不带端口， 默认 80address = hostPortURL.Host + ":80"}}//获得了请求的 host 和 port，向服务端发起 tcp 连接server, err := net.Dial("tcp", address)if err != nil {log.Println(err)return}//如果使用 https 协议，需先向客户端表示连接建立完毕if method == "CONNECT" {fmt.Fprint(client, "HTTP/1.1 200 Connection established\r\n\r\n")} else { //如果使用 http 协议，需将从客户端得到的 http 请求转发给服务端server.Write(b[:n])}//将客户端的请求转发至服务端，将服务端的响应转发给客户端。io.Copy 为阻塞函数，文件描述符不关闭就不停止go io.Copy(server, client)io.Copy(client, server)
}