pkg/archive: Canonicalize stored paths

Currently pkg/archive stores nested windows files with
backslashes (e.g. `dir\`, `dir\file.txt`) and this causes
tar not being correctly extracted on Linux daemon.

This change assures we canonicalize all paths to unix
paths and add them to tar with that name independent of platform.

Fixes the following test cases for Windows CI:
- TestBuildAddFileWithWhitespace
- TestBuildCopyFileWithWhitespace
- TestBuildAddDirContentToRoot
- TestBuildAddDirContentToExistingDir
- TestBuildCopyDirContentToRoot
- TestBuildCopyDirContentToExistDir
- TestBuildDockerignore
- TestBuildEnvUsage
- TestBuildEnvUsage2

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>

archive/archive.go

@@ -172,6 +172,21 @@ type tarAppender struct {
 	SeenFiles map[uint64]string
 }
 
+// canonicalTarName provides a platform-independent and consistent posix-style
+//path for files and directories to be archived regardless of the platform.
+func canonicalTarName(name string, isDir bool) (string, error) {
+	name, err := canonicalTarNameForPath(name)
+	if err != nil {
+		return "", err
+	}
+
+	// suffix with '/' for directories
+	if isDir && !strings.HasSuffix(name, "/") {
+		name += "/"
+	}
+	return name, nil
+}
+
 func (ta *tarAppender) addTarFile(path, name string) error {
 	fi, err := os.Lstat(path)
 	if err != nil {
@@ -190,10 +205,10 @@ func (ta *tarAppender) addTarFile(path, name string) error {
 		return err
 	}
 
-	if fi.IsDir() && !strings.HasSuffix(name, "/") {
-		name = name + "/"
+	name, err = canonicalTarName(name, fi.IsDir())
+	if err != nil {
+		return fmt.Errorf("tar: cannot canonicalize path: %v", err)
 	}
-
 	hdr.Name = name
 
 	nlink, inode, err := setHeaderForSpecialDevice(hdr, ta, name, fi.Sys())