commandconn: don't return error if command closed successfully

---
commandconn: fix race on `Close()`

During normal operation, if a `Read()` or `Write()` call results
in an EOF, we call `onEOF()` to handle the terminating command,
and store it's exit value.

However, if a Read/Write call was blocked while `Close()` is called
the in/out pipes are immediately closed which causes an EOF to be
returned. Here, we shouldn't call `onEOF()`, since the reason why
we got an EOF is because we're already terminating the connection.
This also prevents a race between two calls to the commands `Wait()`,
in the `Close()` call and `onEOF()`

---
Add CLI init timeout to SSH connections

---
connhelper: add 30s ssh default dialer timeout

(same as non-ssh dialer)

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

Author: laurazard

cli/command/cli.go

@@ -8,7 +8,6 @@ import (
 	"path/filepath"
 	"runtime"
 	"strconv"
-	"strings"
 	"sync"
 	"time"
 
@@ -327,13 +326,8 @@ func (cli *DockerCli) getInitTimeout() time.Duration {
 
 func (cli *DockerCli) initializeFromClient() {
 	ctx := context.Background()
-	if !strings.HasPrefix(cli.dockerEndpoint.Host, "ssh://") {
-		// @FIXME context.WithTimeout doesn't work with connhelper / ssh connections
-		// time="2020-04-10T10:16:26Z" level=warning msg="commandConn.CloseWrite: commandconn: failed to wait: signal: killed"
-		var cancel func()
-		ctx, cancel = context.WithTimeout(ctx, cli.getInitTimeout())
-		defer cancel()
-	}
+	ctx, cancel := context.WithTimeout(ctx, cli.getInitTimeout())
+	defer cancel()
 
 	ping, err := cli.client.Ping(ctx)
 	if err != nil {

cli/connhelper/commandconn/commandconn.go

@@ -24,6 +24,7 @@ import (
 	"runtime"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"syscall"
 	"time"
 
@@ -64,98 +65,79 @@ func New(_ context.Context, cmd string, args ...string) (net.Conn, error) {
 
 // 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
+	cmdMutex     sync.Mutex // for cmd, cmdWaitErr
+	cmd          *exec.Cmd
+	cmdWaitErr   error
+	cmdExited    atomic.Bool
+	stdin        io.WriteCloser
+	stdout       io.ReadCloser
+	stderrMu     sync.Mutex // for stderr
+	stderr       bytes.Buffer
+	stdinClosed  atomic.Bool
+	stdoutClosed atomic.Bool
+	closing      atomic.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 {
+// kill returns nil if the command terminated, regardless to the exit status.
+func (c *commandConn) kill() error {
+	if c.cmdExited.Load() {
 		return nil
 	}
-	return c.kill()
-}
-
-// killAndWait tries sending SIGTERM to the process before sending SIGKILL.
-func killAndWait(cmd *exec.Cmd) error {
+	c.cmdMutex.Lock()
 	var werr error
 	if runtime.GOOS != "windows" {
 		werrCh := make(chan error)
-		go func() { werrCh <- cmd.Wait() }()
-		cmd.Process.Signal(syscall.SIGTERM)
+		go func() { werrCh <- c.cmd.Wait() }()
+		c.cmd.Process.Signal(syscall.SIGTERM)
 		select {
 		case werr = <-werrCh:
 		case <-time.After(3 * time.Second):
-			cmd.Process.Kill()
+			c.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.cmd.Process.Kill()
+		werr = c.cmd.Wait()
 	}
+	c.cmdWaitErr = werr
 	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")
+	c.cmdExited.Store(true)
+	return nil
 }
 
+// onEOF gets called if we receive an io.EOF while reading
+// or writing from the undelying command pipes.
+//
+// When we've received an EOF we expect that the command will
+// be terminated soon. As such, we call Wait() on the command
+// and return EOF or the error depending on whether the command
+// exited with an error.
+//
+// If Wait() does not return within 10s, an error is returned
 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 {
+	defer c.cmdMutex.Unlock()
+
+	var werr error
+	if c.cmdExited.Load() {
 		werr = c.cmdWaitErr
 	} else {
 		werrCh := make(chan error)
 		go func() { werrCh <- c.cmd.Wait() }()
 		select {
 		case werr = <-werrCh:
 			c.cmdWaitErr = werr
-			c.cmdExited = true
+			c.cmdExited.Store(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
 	}
@@ -178,59 +160,102 @@ func ignorableCloseError(err error) bool {
 	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)
+func (c *commandConn) Read(p []byte) (int, error) {
+	n, err := c.stdout.Read(p)
+	// check after the call to Read, since
+	// it is blocking, and while waiting on it
+	// Close might get called
+	if c.closing.Load() {
+		// If we're currently closing the connection
+		// we don't want to call onEOF, but we do want
+		// to return an io.EOF
+		return 0, io.EOF
 	}
-	c.stdioClosedMu.Lock()
-	c.stdoutClosed = true
-	c.stdioClosedMu.Unlock()
-	if err := c.killIfStdioClosed(); err != nil {
-		logrus.Warnf("commandConn.CloseRead: %v", err)
+
+	if err == io.EOF {
+		err = c.onEOF(err)
 	}
-	return nil
+	return n, err
 }
 
-func (c *commandConn) Read(p []byte) (int, error) {
-	n, err := c.stdout.Read(p)
+func (c *commandConn) Write(p []byte) (int, error) {
+	n, err := c.stdin.Write(p)
+	// check after the call to Write, since
+	// it is blocking, and while waiting on it
+	// Close might get called
+	if c.closing.Load() {
+		// If we're currently closing the connection
+		// we don't want to call onEOF, but we do want
+		// to return an io.EOF
+		return 0, io.EOF
+	}
+
 	if err == io.EOF {
 		err = c.onEOF(err)
 	}
 	return n, err
 }
 
-func (c *commandConn) CloseWrite() error {
+// CloseRead allows commandConn to implement halfCloser
+func (c *commandConn) CloseRead() error {
 	// NOTE: maybe already closed here
-	if err := c.stdin.Close(); err != nil && !ignorableCloseError(err) {
-		logrus.Warnf("commandConn.CloseWrite: %v", err)
+	if err := c.stdout.Close(); err != nil && !ignorableCloseError(err) {
+		logrus.Warnf("commandConn.CloseRead: %v", err)
+		return err
 	}
-	c.stdioClosedMu.Lock()
-	c.stdinClosed = true
-	c.stdioClosedMu.Unlock()
-	if err := c.killIfStdioClosed(); err != nil {
-		logrus.Warnf("commandConn.CloseWrite: %v", err)
+	c.stdoutClosed.Store(true)
+
+	if c.stdinClosed.Load() {
+		if err := c.kill(); err != nil {
+			logrus.Warnf("commandConn.CloseRead: %v", err)
+			return 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)
+// CloseWrite allows commandConn to implement halfCloser
+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)
+		return err
 	}
-	return n, err
+	c.stdinClosed.Store(true)
+
+	if c.stdoutClosed.Load() {
+		if err := c.kill(); err != nil {
+			logrus.Warnf("commandConn.CloseWrite: %v", err)
+			return err
+		}
+	}
+
+	return nil
 }
 
+// Close is the net.Conn func that gets called
+// by the transport when a dial is cancelled
+// due to it's context timing out. Any blocked
+// Read or Write calls will be unblocked and
+// return errors. It will block until the underlying
+// command has terminated.
 func (c *commandConn) Close() error {
-	var err error
-	if err = c.CloseRead(); err != nil {
+	c.closing.Store(true)
+	defer c.closing.Store(false)
+
+	err := c.CloseRead()
+	if err != nil {
 		logrus.Warnf("commandConn.Close: CloseRead: %v", err)
+		return err
 	}
-	if err = c.CloseWrite(); err != nil {
+	err = c.CloseWrite()
+	if err != nil {
 		logrus.Warnf("commandConn.Close: CloseWrite: %v", err)
+		return err
 	}
-	return err
+
+	return nil
 }
 
 func (c *commandConn) LocalAddr() net.Addr {