内网穿透原理及frp核心代码解析

服务端设置(frps.ini)：
[common]
bind_port = 7000       //此处填写客户端监听的服务端端口号
vhost_http_port = 8080 //此处填写用户访问的端口号

客户端配置(frpc.ini)：
[common]
server_addr = x.x.x.x //此处填写服务端 IP 地址
server_port = 7000    //此处填写服务端配置的bind_port

[web]
type = http         //此处规定转发请求的协议类型
local_port = 80     //此处规定本地服务启动的地址
custom_domains = www.example.com   //此处可以填写自定义域名（需要在 IP 地址下配置域名解析）

func runServer(cfg config.ServerCommonConf) (err error) {
  log.InitLog(cfg.LogWay, cfg.LogFile, cfg.LogLevel, cfg.LogMaxDays, cfg.DisableLogColor)

  if cfgFile != "" {
    log.Info("frps uses config file: %s", cfgFile)
  } else {
    log.Info("frps uses command line arguments for config")
  }
  
  // !important 核心代码1
  svr, err := server.NewService(cfg)
  if err != nil {
    return err
  }
  log.Info("frps started successfully")
  // !important 核心代码2
  svr.Run()
  return
}

for{    
  // !important 核心代码3
conn, session, err := svr.login()
    if err != nil {
      xl.Warn("login to server failed: %v", err)

      // if login_fail_exit is true, just exit this program
      // otherwise sleep a while and try again to connect to server
      if svr.cfg.LoginFailExit {
        return err
      }
      util.RandomSleep(10*time.Second, 0.9, 1.1)
    } else {
      // login success
      // !important 核心代码4
      ctl := NewControl(svr.ctx, svr.runID, conn, session, svr.cfg, svr.pxyCfgs, svr.visitorCfgs, svr.serverUDPPort, svr.authSetter)
      ctl.Run()
      svr.ctlMu.Lock()
      svr.ctl = ctl
      svr.ctlMu.Unlock()
      break
    }
}

func (pxy *BaseProxy) GetWorkConnFromPool(src, dst net.Addr) (workConn net.Conn, err error) {
  xl := xlog.FromContextSafe(pxy.ctx)
  // try all connections from the pool
  for i := 0; i < pxy.poolCount+1; i++ {
    // !important 核心代码5
    if workConn, err = pxy.getWorkConnFn(); err != nil {
      xl.Warn("failed to get work connection: %v", err)
      return
    }
    xl.Debug("get a new work connection: [%s]", workConn.RemoteAddr().String())
    xl.Spawn().AppendPrefix(pxy.GetName())
    workConn = frpNet.NewContextConn(pxy.ctx, workConn)
    ......
    // !important 核心代码6
    err := msg.WriteMsg(workConn, &msg.StartWorkConn{
      ProxyName: pxy.GetName(),
      SrcAddr:   srcAddr,
      SrcPort:   uint16(srcPort),
      DstAddr:   dstAddr,
      DstPort:   uint16(dstPort),
      Error:     "",
    })
  }
}

func (pxy *TCPProxy) InWorkConn(conn net.Conn, m *msg.StartWorkConn) {
  // !important 核心代码7
  HandleTCPWorkConnection(pxy.ctx, &pxy.cfg.LocalSvrConf, pxy.proxyPlugin, pxy.cfg.GetBaseInfo(), pxy.limiter,
    conn, []byte(pxy.clientCfg.Token), m)
}

func (ctl *Control) writer() {
  xl := ctl.xl
  defer func() {
    if err := recover(); err != nil {
      xl.Error("panic error: %v", err)
      xl.Error(string(debug.Stack()))
    }
  }()

  defer ctl.allShutdown.Start()
  defer ctl.writerShutdown.Done()

  encWriter, err := crypto.NewWriter(ctl.conn, []byte(ctl.serverCfg.Token))
  if err != nil {
    xl.Error("crypto new writer error: %v", err)
    ctl.allShutdown.Start()
    return
  }
  for {
    m, ok := <-ctl.sendCh
    if !ok {
      xl.Info("control writer is closing")
      return
    }
    // !important 核心代码8
    if err := msg.WriteMsg(encWriter, m); err != nil {
      xl.Warn("write message to control connection error: %v", err)
      return
    }
  }
}

// !important 核心代码9
func (ctl *Control) reader() {
  xl := ctl.xl
  defer func() {
    if err := recover(); err != nil {
      xl.Error("panic error: %v", err)
      xl.Error(string(debug.Stack()))
    }
  }()
  defer ctl.readerShutdown.Done()
  defer close(ctl.closedCh)

  encReader := crypto.NewReader(ctl.conn, []byte(ctl.clientCfg.Token))
  for {
    m, err := msg.ReadMsg(encReader)
    if err != nil {
      if err == io.EOF {
        xl.Debug("read from control connection EOF")
        return
      }
      xl.Warn("read error: %v", err)
      ctl.conn.Close()
      return
    }
    ctl.readCh <- m
  }
}