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commandconn.go
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commandconn.go
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// Package commandconn provides a net.Conn implementation that can be used for
// proxying (or emulating) stream via a custom command.
//
// For example, to provide an http.Client that can connect to a Docker daemon
// running in a Docker container ("DIND"):
//
// httpClient := &http.Client{
// Transport: &http.Transport{
// DialContext: func(ctx context.Context, _network, _addr string) (net.Conn, error) {
// return commandconn.New(ctx, "docker", "exec", "-it", containerID, "docker", "system", "dial-stdio")
// },
// },
// }
package commandconn
import (
"bytes"
"context"
"fmt"
"io"
"net"
"os"
"runtime"
"strings"
"sync"
"syscall"
"time"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
exec "golang.org/x/sys/execabs"
)
// New returns net.Conn
func New(_ context.Context, cmd string, args ...string) (net.Conn, error) {
var (
c commandConn
err error
)
c.cmd = exec.Command(cmd, args...)
// we assume that args never contains sensitive information
logrus.Debugf("commandconn: starting %s with %v", cmd, args)
c.cmd.Env = os.Environ()
c.cmd.SysProcAttr = &syscall.SysProcAttr{}
setPdeathsig(c.cmd)
createSession(c.cmd)
c.stdin, err = c.cmd.StdinPipe()
if err != nil {
return nil, err
}
c.stdout, err = c.cmd.StdoutPipe()
if err != nil {
return nil, err
}
c.cmd.Stderr = &stderrWriter{
stderrMu: &c.stderrMu,
stderr: &c.stderr,
debugPrefix: fmt.Sprintf("commandconn (%s):", cmd),
}
c.localAddr = dummyAddr{network: "dummy", s: "dummy-0"}
c.remoteAddr = dummyAddr{network: "dummy", s: "dummy-1"}
return &c, c.cmd.Start()
}
// commandConn implements net.Conn
type commandConn struct {
cmd *exec.Cmd
cmdExited bool
cmdWaitErr error
cmdMutex sync.Mutex
stdin io.WriteCloser
stdout io.ReadCloser
stderrMu sync.Mutex
stderr bytes.Buffer
stdioClosedMu sync.Mutex // for stdinClosed and stdoutClosed
stdinClosed bool
stdoutClosed bool
localAddr net.Addr
remoteAddr net.Addr
}
// killIfStdioClosed kills the cmd if both stdin and stdout are closed.
func (c *commandConn) killIfStdioClosed() error {
c.stdioClosedMu.Lock()
stdioClosed := c.stdoutClosed && c.stdinClosed
c.stdioClosedMu.Unlock()
if !stdioClosed {
return nil
}
return c.kill()
}
// killAndWait tries sending SIGTERM to the process before sending SIGKILL.
func killAndWait(cmd *exec.Cmd) error {
var werr error
if runtime.GOOS != "windows" {
werrCh := make(chan error)
go func() { werrCh <- cmd.Wait() }()
cmd.Process.Signal(syscall.SIGTERM)
select {
case werr = <-werrCh:
case <-time.After(3 * time.Second):
cmd.Process.Kill()
werr = <-werrCh
}
} else {
cmd.Process.Kill()
werr = cmd.Wait()
}
return werr
}
// kill returns nil if the command terminated, regardless to the exit status.
func (c *commandConn) kill() error {
var werr error
c.cmdMutex.Lock()
if c.cmdExited {
werr = c.cmdWaitErr
} else {
werr = killAndWait(c.cmd)
c.cmdWaitErr = werr
c.cmdExited = true
}
c.cmdMutex.Unlock()
if werr == nil {
return nil
}
wExitErr, ok := werr.(*exec.ExitError)
if ok {
if wExitErr.ProcessState.Exited() {
return nil
}
}
return errors.Wrapf(werr, "commandconn: failed to wait")
}
func (c *commandConn) onEOF(eof error) error {
// when we got EOF, the command is going to be terminated
var werr error
c.cmdMutex.Lock()
if c.cmdExited {
werr = c.cmdWaitErr
} else {
werrCh := make(chan error)
go func() { werrCh <- c.cmd.Wait() }()
select {
case werr = <-werrCh:
c.cmdWaitErr = werr
c.cmdExited = true
case <-time.After(10 * time.Second):
c.cmdMutex.Unlock()
c.stderrMu.Lock()
stderr := c.stderr.String()
c.stderrMu.Unlock()
return errors.Errorf("command %v did not exit after %v: stderr=%q", c.cmd.Args, eof, stderr)
}
}
c.cmdMutex.Unlock()
if werr == nil {
return eof
}
c.stderrMu.Lock()
stderr := c.stderr.String()
c.stderrMu.Unlock()
return errors.Errorf("command %v has exited with %v, please make sure the URL is valid, and Docker 18.09 or later is installed on the remote host: stderr=%s", c.cmd.Args, werr, stderr)
}
func ignorableCloseError(err error) bool {
errS := err.Error()
ss := []string{
os.ErrClosed.Error(),
}
for _, s := range ss {
if strings.Contains(errS, s) {
return true
}
}
return false
}
func (c *commandConn) CloseRead() error {
// NOTE: maybe already closed here
if err := c.stdout.Close(); err != nil && !ignorableCloseError(err) {
logrus.Warnf("commandConn.CloseRead: %v", err)
}
c.stdioClosedMu.Lock()
c.stdoutClosed = true
c.stdioClosedMu.Unlock()
if err := c.killIfStdioClosed(); err != nil {
logrus.Warnf("commandConn.CloseRead: %v", err)
}
return nil
}
func (c *commandConn) Read(p []byte) (int, error) {
n, err := c.stdout.Read(p)
if err == io.EOF {
err = c.onEOF(err)
}
return n, err
}
func (c *commandConn) CloseWrite() error {
// NOTE: maybe already closed here
if err := c.stdin.Close(); err != nil && !ignorableCloseError(err) {
logrus.Warnf("commandConn.CloseWrite: %v", err)
}
c.stdioClosedMu.Lock()
c.stdinClosed = true
c.stdioClosedMu.Unlock()
if err := c.killIfStdioClosed(); err != nil {
logrus.Warnf("commandConn.CloseWrite: %v", err)
}
return nil
}
func (c *commandConn) Write(p []byte) (int, error) {
n, err := c.stdin.Write(p)
if err == io.EOF {
err = c.onEOF(err)
}
return n, err
}
func (c *commandConn) Close() error {
var err error
if err = c.CloseRead(); err != nil {
logrus.Warnf("commandConn.Close: CloseRead: %v", err)
}
if err = c.CloseWrite(); err != nil {
logrus.Warnf("commandConn.Close: CloseWrite: %v", err)
}
return err
}
func (c *commandConn) LocalAddr() net.Addr {
return c.localAddr
}
func (c *commandConn) RemoteAddr() net.Addr {
return c.remoteAddr
}
func (c *commandConn) SetDeadline(t time.Time) error {
logrus.Debugf("unimplemented call: SetDeadline(%v)", t)
return nil
}
func (c *commandConn) SetReadDeadline(t time.Time) error {
logrus.Debugf("unimplemented call: SetReadDeadline(%v)", t)
return nil
}
func (c *commandConn) SetWriteDeadline(t time.Time) error {
logrus.Debugf("unimplemented call: SetWriteDeadline(%v)", t)
return nil
}
type dummyAddr struct {
network string
s string
}
func (d dummyAddr) Network() string {
return d.network
}
func (d dummyAddr) String() string {
return d.s
}
type stderrWriter struct {
stderrMu *sync.Mutex
stderr *bytes.Buffer
debugPrefix string
}
func (w *stderrWriter) Write(p []byte) (int, error) {
logrus.Debugf("%s%s", w.debugPrefix, string(p))
w.stderrMu.Lock()
if w.stderr.Len() > 4096 {
w.stderr.Reset()
}
n, err := w.stderr.Write(p)
w.stderrMu.Unlock()
return n, err
}