golang hijack
一直不太明白golang的hijack是干什么的？只知道hijack这个词是篡取的意思，难道跟网关的作用一样，把client的请求发到这个服务上，然后这个服务帮忙转发到远端server，但是看了源码后就明白这个golang hijack是干嘛的？
先看一下hijack相关的结构说明：
type Hijacker interface {
Hijack() (net.Conn, *bufio.ReadWriter, error)
}
//返回连接接口net.Conn和ReadWriter,bufio读写的
// Hijack lets the caller take over the connection. -----翻译Hijack让调用者管理连接
// After a call to Hijack(), the HTTP server library
// will not do anything else with the connection.
// It becomes the caller's responsibility to manage
// and close the connection.
------------翻译调用Hijack后，HTTP的server不会对连接做多余的处理让用户自己管理和关闭连接
再看一下docker中对hijack的使用
dial, err := cli.dial() //设置TCP keepAlive做长连接
// When we set up a TCP connection for hijack, there could be long periods
// of inactivity (a long running command with no output) that in certain
// network setups may cause ECONNTIMEOUT, leaving the client in an unknown
// state. Setting TCP KeepAlive on the socket connection will prohibit
// ECONNTIMEOUT unless the socket connection truly is broken
if tcpConn, ok := dial.(*net.TCPConn); ok {
tcpConn.SetKeepAlive(true)
tcpConn.SetKeepAlivePeriod(30 * time.Second)
}
if err != nil {
if strings.Contains(err.Error(), "connection refused") {
return fmt.Errorf("Cannot connect to the Docker daemon. Is 'docker daemon' running on this host?")
}
return err
}
clientconn := httputil.NewClientConn(dial, nil)
defer clientconn.Close()
// Server hijacks the connection, error 'connection closed' expected
clientconn.Do(req)
rwc, br := clientconn.Hijack()
//清理掉buffer 这步非常重要,返回这个两个参数就是给用户自己管理连接和数据处理
defer rwc.Close()
再看看clientconn.Hijack的实现：
func (cc *ClientConn) Hijack() (c net.Conn, r *bufio.Reader) {
cc.lk.Lock()
defer cc.lk.Unlock()
c = cc.c
r = cc.r
cc.c = nil
cc.r = nil
return
}
//就是在NewClientConn时候保存的net.Conn和bufio.Reader
func NewClientConn(c net.Conn, r *bufio.Reader) *ClientConn {
if r == nil {
r = bufio.NewReader(c)
}
return &ClientConn{
c: c,
r: r,
pipereq: make(map[*http.Request]uint),
writeReq: (*http.Request).Write,
}
}
最后截取部分server端针对hijack的处理：
func (c *conn) serve() {
origConn := c.rwc // copy it before it's set nil on Close or Hijack
defer func() {
if err := recover(); err != nil {
const size = 64 << 10
buf := make([]byte, size)
buf = buf[:runtime.Stack(buf, false)]
c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
}
//从这里看出来hijacked状态服务端不close
if !c.hijacked() {
c.close()
c.setState(origConn, StateClosed)
}
}()
/* ...................... */
}
总结：hijack就是不用重新建立连接或者重新构造ClientConn设置net.Conn和bufio，然后不断复用net.Conn和bufio，自己管理