golang實現TCP代理

前言

TCP代理的使用場景有很多，比如Nginx的http代理，本質上也是TCP的轉發，微服務網格istio的Envoy也是基於這種理念來實現的。

 

之所以寫這個demo，是為了可以很方便地調試上下游服務在通信過程中到底傳遞了什么數據，對各種協議的通信方式可以很快的掌握它們原理，比如rpc通信、http通信、grpc通信等等。

 

代碼路徑：http://gitee.com/zqwlai/go-test/tcpProxy.go

 

package main import ( "bufio"
    "flag"
    "fmt"
    "github.com/rs/zerolog"
    "net"
    "os"
    "strconv"
    "strings"

    "time" ) var logger = zerolog.New(os.Stdout).With().Timestamp().Logger() func main() { help := flag.Bool("help", false, "print usage") bind := flag.String("bind", "0.0.0.0:9528", "The address to bind to") backend := flag.String("backend", "127.0.0.1:30000", "The backend server address") flag.Parse() logger.Level(zerolog.DebugLevel) if *help { flag.Usage() return } if *backend == "" { flag.Usage() return } if *bind == "" { //use default bind
        logger.Info().Str("bind", *bind).Msg("use default bind") } success, err := RunProxy(*bind, *backend) if !success { logger.Error().Err(err).Send() os.Exit(1) } } func RunProxy(bind, backend string) (bool, error) { listener, err := net.Listen("tcp", bind) if err != nil { return false, err } defer listener.Close() logger.Info().Str("bind", bind).Str("backend", backend).Msg("tcp-proxy started.") for { conn, err := listener.Accept() if err != nil { logger.Error().Err(err).Send() } else { go ConnectionHandler(conn, backend) } } } func ConnectionHandler(conn net.Conn, backend string) { logger.Info().Str("conn", conn.RemoteAddr().String()).Msg("client connected.") target, err := net.Dial("tcp", backend) defer conn.Close() if err != nil { logger.Error().Err(err).Send() } else { defer target.Close() logger.Info().Str("conn", conn.RemoteAddr().String()).Str("backend", target.LocalAddr().String()).Msg("backend connected.") closed := make(chan bool, 1) go Proxy(conn, target, closed) go Proxy2(target, conn, closed) <-closed logger.Info().Str("conn", conn.RemoteAddr().String()).Msg("Connection closed.") } } func Proxy(from net.Conn, to net.Conn, closed chan bool) { buffer := make([]byte, 4096) for { n1, err := from.Read(buffer) if err != nil { closed <- true
            return } fmt.Println(1111, n1) fmt.Println(222, string(buffer[:n1])) n2, err := to.Write(buffer[:n1]) logger.Debug().Str("from", from.RemoteAddr().String()).Int("recv", n1).Str("to", to.RemoteAddr().String()).Int("send", n2).Send() if err != nil { closed <- true
            return } } } func Proxy2(from net.Conn, to net.Conn, closed chan bool) { time.Sleep(1*time.Second) buffer := make([]byte, 4096) for { n1, err := from.Read(buffer) if err != nil { closed <- true
            return } fmt.Println(3333, string(buffer[:n1])) n2, err := to.Write(buffer[:n1]) logger.Debug().Str("from", from.RemoteAddr().String()).Int("recv", n1).Str("to", to.RemoteAddr().String()).Int("send", n2).Send() if err != nil { closed <- true
            return } } } //解析HTTP報文
func parseHttp(conn net.Conn)(string){ var s = "" reader := bufio.NewReader(conn) firstLine,_,_ := reader.ReadLine() s += string(firstLine) + "\n" tempList := strings.Split(string(firstLine), " ") method := tempList[0] path := tempList[1] proto := tempList[2] fmt.Println(1111, method, path, proto) var headers = make(map[string]string) var contenLength int
    for { line,_,_ := reader.ReadLine() s += string(line) + "\n"
        if len(line) == 0{ break } tempList = strings.Split(string(line), ":") key := tempList[0] value := strings.Trim(tempList[1], " ") headers[key] = value if (key == "Content-Length"){ contenLength,_ = strconv.Atoi(value) } } fmt.Println(2222, headers) if contenLength == 0{ return s } pack := make([]byte, contenLength) t,_ := reader.Read(pack) s += string(pack[:t]) return s }

 

 

 

簡單說下原理，proxy在收到下游的請求后，會建立一個conn1，此時proxy會解析conn1里面的目標地址，並與之建立TCP連接conn2， 接下來會開啟兩個協程，一個用來從conn1里讀取請求報文，並將報文發給conn2，另一個協程從conn2讀取響應數據，並寫到conn1返回給上游。