docker_streaming_others.go

// +build !windows,!dockerless

/*
Copyright 2019 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package dockershim

import (
	"bytes"
	"fmt"
	"io"
	"os/exec"
	"strings"

	"k8s.io/klog/v2"
)

func (r *streamingRuntime) portForward(podSandboxID string, port int32, stream io.ReadWriteCloser) error {
	container, err := r.client.InspectContainer(podSandboxID)
	if err != nil {
		return err
	}

	if !container.State.Running {
		return fmt.Errorf("container not running (%s)", container.ID)
	}

	containerPid := container.State.Pid
	socatPath, lookupErr := exec.LookPath("socat")
	if lookupErr != nil {
		return fmt.Errorf("unable to do port forwarding: socat not found")
	}

	args := []string{"-t", fmt.Sprintf("%d", containerPid), "-n", socatPath, "-", fmt.Sprintf("TCP4:localhost:%d", port)}

	nsenterPath, lookupErr := exec.LookPath("nsenter")
	if lookupErr != nil {
		return fmt.Errorf("unable to do port forwarding: nsenter not found")
	}

	commandString := fmt.Sprintf("%s %s", nsenterPath, strings.Join(args, " "))
	klog.V(4).Infof("executing port forwarding command: %s", commandString)

	command := exec.Command(nsenterPath, args...)
	command.Stdout = stream

	stderr := new(bytes.Buffer)
	command.Stderr = stderr

	// If we use Stdin, command.Run() won't return until the goroutine that's copying
	// from stream finishes. Unfortunately, if you have a client like telnet connected
	// via port forwarding, as long as the user's telnet client is connected to the user's
	// local listener that port forwarding sets up, the telnet session never exits. This
	// means that even if socat has finished running, command.Run() won't ever return
	// (because the client still has the connection and stream open).
	//
	// The work around is to use StdinPipe(), as Wait() (called by Run()) closes the pipe
	// when the command (socat) exits.
	inPipe, err := command.StdinPipe()
	if err != nil {
		return fmt.Errorf("unable to do port forwarding: error creating stdin pipe: %v", err)
	}
	go func() {
		io.Copy(inPipe, stream)
		inPipe.Close()
	}()

	if err := command.Run(); err != nil {
		return fmt.Errorf("%v: %s", err, stderr.String())
	}

	return nil
}