Only copy new or modified files into VM on restart

When minikube restarts, we can save time by only copying over files that
have changes or don't exist in the VM. The code in this PR first checks
if the file already exists in the VM, and skips copying it over again if
it does.

pkg/minikube/assets/vm_assets.go

@@ -23,6 +23,7 @@ import (
 	"io"
 	"os"
 	"path"
+	"time"
 
 	"github.com/golang/glog"
 	"github.com/pkg/errors"
@@ -36,6 +37,7 @@ type CopyableFile interface {
 	GetTargetDir() string
 	GetTargetName() string
 	GetPermissions() string
+	GetModTime() time.Time
 }
 
 // BaseAsset is the base asset class
@@ -66,6 +68,11 @@ func (b *BaseAsset) GetPermissions() string {
 	return b.Permissions
 }
 
+// GetModTime returns mod time
+func (b *BaseAsset) GetModTime() time.Time {
+	return time.Time{}
+}
+
 // FileAsset is an asset using a file
 type FileAsset struct {
 	BaseAsset
@@ -104,6 +111,15 @@ func (f *FileAsset) GetLength() (flen int) {
 	return int(fi.Size())
 }
 
+// GetModTime returns modification time of the file
+func (f *FileAsset) GetModTime() time.Time {
+	fi, err := os.Stat(f.AssetName)
+	if err != nil {
+		return time.Time{}
+	}
+	return fi.ModTime()
+}
+
 func (f *FileAsset) Read(p []byte) (int, error) {
 	if f.reader == nil {
 		return 0, errors.New("Error attempting FileAsset.Read, FileAsset.reader uninitialized")

pkg/minikube/command/ssh_runner.go

@@ -23,6 +23,8 @@ import (
 	"io"
 	"os/exec"
 	"path"
+	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -143,6 +145,12 @@ func (s *SSHRunner) RunCmd(cmd *exec.Cmd) (*RunResult, error) {
 
 // Copy copies a file to the remote over SSH.
 func (s *SSHRunner) Copy(f assets.CopyableFile) error {
+	dst := path.Join(path.Join(f.GetTargetDir(), f.GetTargetName()))
+	if s.fileExistsInVM(f, dst) {
+		glog.Infof("Skipping copying %s as it already exists", f.GetAssetName())
+		return nil
+	}
+
 	sess, err := s.c.NewSession()
 	if err != nil {
 		return errors.Wrap(err, "NewSession")
@@ -156,7 +164,6 @@ func (s *SSHRunner) Copy(f assets.CopyableFile) error {
 	// StdinPipe is closed. But let's use errgroup to make it explicit.
 	var g errgroup.Group
 	var copied int64
-	dst := path.Join(path.Join(f.GetTargetDir(), f.GetTargetName()))
 	glog.Infof("Transferring %d bytes to %s", f.GetLength(), dst)
 
 	g.Go(func() error {
@@ -189,6 +196,49 @@ func (s *SSHRunner) Copy(f assets.CopyableFile) error {
 	return g.Wait()
 }
 
+func (s *SSHRunner) fileExistsInVM(f assets.CopyableFile, dst string) bool {
+	sess, err := s.c.NewSession()
+	if err != nil {
+		return false
+	}
+
+	// check if sizes of the two files are the same
+	srcSize := f.GetLength()
+	size := fmt.Sprintf("ls -l %s | cut -d \" \" -f5", dst)
+	out, err := sess.CombinedOutput(size)
+	if err != nil {
+		return false
+	}
+	dstSize, err := strconv.Atoi(strings.Trim(string(out), "\n"))
+	if err != nil {
+		return false
+	}
+	if srcSize != dstSize {
+		return false
+	}
+
+	sess, err = s.c.NewSession()
+	if err != nil {
+		return false
+	}
+	// ensure src file hasn't been modified since dst was copied over
+	srcModTime := f.GetModTime()
+	stat := "stat -c %Y" + fmt.Sprintf(" %s", dst)
+	out, err = sess.CombinedOutput(stat)
+	if err != nil {
+		return false
+	}
+	unix, err := strconv.Atoi(strings.Trim(string(out), "\n"))
+	if err != nil {
+		return false
+	}
+	dstModTime := time.Unix(int64(unix), 0)
+	if err != nil {
+		return false
+	}
+	return srcModTime.Before(dstModTime)
+}
+
 // teePrefix copies bytes from a reader to writer, logging each new line.
 func teePrefix(prefix string, r io.Reader, w io.Writer, logger func(format string, args ...interface{})) error {
 	scanner := bufio.NewScanner(r)