engine-api/client/hijack.go

package lib

import (
	"crypto/tls"
	"errors"
	"fmt"
	"net"
	"net/http/httputil"
	"net/url"
	"strings"
	"time"

	"github.com/docker/docker/api/types"
)

// tlsClientCon holds tls information and a dialed connection.
type tlsClientCon struct {
	*tls.Conn
	rawConn net.Conn
}

func (c *tlsClientCon) CloseWrite() error {
	// Go standard tls.Conn doesn't provide the CloseWrite() method so we do it
	// on its underlying connection.
	if conn, ok := c.rawConn.(types.CloseWriter); ok {
		return conn.CloseWrite()
	}
	return nil
}

// postHijacked sends a POST request and hijacks the connection.
func (cli *Client) postHijacked(path string, query url.Values, body interface{}, headers map[string][]string) (types.HijackedResponse, error) {
	bodyEncoded, err := encodeData(body)
	if err != nil {
		return types.HijackedResponse{}, err
	}

	req, err := cli.newRequest("POST", path, query, bodyEncoded, headers)
	if err != nil {
		return types.HijackedResponse{}, err
	}
	req.Host = cli.Addr

	req.Header.Set("Connection", "Upgrade")
	req.Header.Set("Upgrade", "tcp")

	conn, err := dial(cli.Proto, cli.Addr, cli.tlsConfig)
	if err != nil {
		if strings.Contains(err.Error(), "connection refused") {
			return types.HijackedResponse{}, fmt.Errorf("Cannot connect to the Docker daemon. Is 'docker daemon' running on this host?")
		}
		return types.HijackedResponse{}, err
	}

	// 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 := conn.(*net.TCPConn); ok {
		tcpConn.SetKeepAlive(true)
		tcpConn.SetKeepAlivePeriod(30 * time.Second)
	}

	clientconn := httputil.NewClientConn(conn, nil)
	defer clientconn.Close()

	// Server hijacks the connection, error 'connection closed' expected
	clientconn.Do(req)

	rwc, br := clientconn.Hijack()

	return types.HijackedResponse{rwc, br}, nil
}

func tlsDial(network, addr string, config *tls.Config) (net.Conn, error) {
	return tlsDialWithDialer(new(net.Dialer), network, addr, config)
}

// We need to copy Go's implementation of tls.Dial (pkg/cryptor/tls/tls.go) in
// order to return our custom tlsClientCon struct which holds both the tls.Conn
// object _and_ its underlying raw connection. The rationale for this is that
// we need to be able to close the write end of the connection when attaching,
// which tls.Conn does not provide.
func tlsDialWithDialer(dialer *net.Dialer, network, addr string, config *tls.Config) (net.Conn, error) {
	// We want the Timeout and Deadline values from dialer to cover the
	// whole process: TCP connection and TLS handshake. This means that we
	// also need to start our own timers now.
	timeout := dialer.Timeout

	if !dialer.Deadline.IsZero() {
		deadlineTimeout := dialer.Deadline.Sub(time.Now())
		if timeout == 0 || deadlineTimeout < timeout {
			timeout = deadlineTimeout
		}
	}

	var errChannel chan error

	if timeout != 0 {
		errChannel = make(chan error, 2)
		time.AfterFunc(timeout, func() {
			errChannel <- errors.New("")
		})
	}

	rawConn, err := dialer.Dial(network, addr)
	if err != nil {
		return nil, err
	}
	// 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 := rawConn.(*net.TCPConn); ok {
		tcpConn.SetKeepAlive(true)
		tcpConn.SetKeepAlivePeriod(30 * time.Second)
	}

	colonPos := strings.LastIndex(addr, ":")
	if colonPos == -1 {
		colonPos = len(addr)
	}
	hostname := addr[:colonPos]

	// If no ServerName is set, infer the ServerName
	// from the hostname we're connecting to.
	if config.ServerName == "" {
		// Make a copy to avoid polluting argument or default.
		c := *config
		c.ServerName = hostname
		config = &c
	}

	conn := tls.Client(rawConn, config)

	if timeout == 0 {
		err = conn.Handshake()
	} else {
		go func() {
			errChannel <- conn.Handshake()
		}()

		err = <-errChannel
	}

	if err != nil {
		rawConn.Close()
		return nil, err
	}

	// This is Docker difference with standard's crypto/tls package: returned a
	// wrapper which holds both the TLS and raw connections.
	return &tlsClientCon{conn, rawConn}, nil
}

func dial(proto, addr string, tlsConfig *tls.Config) (net.Conn, error) {
	if tlsConfig != nil && proto != "unix" {
		// Notice this isn't Go standard's tls.Dial function
		return tlsDial(proto, addr, tlsConfig)
	}
	return net.Dial(proto, addr)
}