fixup! RebaseArchiveEntries: fix archive path rebasing

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

copy.go

@@ -317,26 +317,35 @@ func PrepareArchiveCopy(srcContent io.Reader, srcInfo, dstInfo CopyInfo) (dstDir
 }
 
 // rebaseName replaces oldBase with newBase at the beginning of a POSIX-style
-// archive entry name. oldBase and newBase must use forward slashes. It preserves
-// the remainder of the name verbatim and does not clean or canonicalize paths.
+// archive entry name. oldBase and newBase must use forward slashes. When
+// rebasing from the archive root, it removes all leading slashes from the name.
+// It otherwise preserves the remainder verbatim and does not clean or
+// canonicalize paths.
 func rebaseName(name, oldBase, newBase string) string {
+	var remainder string
+
 	if oldBase == "/" {
-		name = strings.TrimPrefix(name, "/")
-		if newBase == "" {
+		remainder = strings.TrimLeft(name, "/")
+	} else {
+		oldBase = strings.TrimSuffix(oldBase, "/")
+		switch {
+		case name == oldBase:
+			remainder = ""
+		case strings.HasPrefix(name, oldBase+"/"):
+			remainder = strings.TrimPrefix(name, oldBase+"/")
+		default:
 			return name
 		}
-
-		// Do not use path.Join; it would clean the archive entry name.
-		return strings.TrimSuffix(newBase, "/") + "/" + name
 	}
 
-	oldBase = strings.TrimSuffix(oldBase, "/")
-	suffix, ok := strings.CutPrefix(name, oldBase)
-	if !ok || suffix != "" && !strings.HasPrefix(suffix, "/") {
-		return name
+	newBase = strings.TrimSuffix(newBase, "/")
+	if newBase == "" {
+		return remainder
 	}
-
-	return strings.TrimSuffix(newBase, "/") + suffix
+	if remainder == "" {
+		return newBase
+	}
+	return newBase + "/" + remainder
 }
 
 // RebaseArchiveEntries rewrites the given srcContent archive replacing

copy_test.go

@@ -34,6 +34,20 @@ func TestRebaseArchiveEntriesPlatformPaths(t *testing.T) {
 			headerName: "/foo/bar",
 			wantName:   "prefix/foo/bar",
 		},
+		{
+			name:       "rebase name with multiple leading slashes from root",
+			oldBase:    "/",
+			newBase:    "prefix",
+			headerName: "///foo/bar",
+			wantName:   "prefix/foo/bar",
+		},
+		{
+			name:       "rebase absolute name from root to empty",
+			oldBase:    "/",
+			newBase:    "",
+			headerName: "/foo/bar",
+			wantName:   "foo/bar",
+		},
 		{
 			name:       "rebase absolute name from root to empty",
 			oldBase:    "/",
@@ -82,6 +96,13 @@ func TestRebaseArchiveEntriesPlatformPaths(t *testing.T) {
 			headerName: "foo/../bar",
 			wantName:   "prefix/foo/../bar",
 		},
+		{
+			name:       "do not rebase partial path component match",
+			oldBase:    "foo",
+			newBase:    "prefix",
+			headerName: "foobar/baz",
+			wantName:   "foobar/baz",
+		},
 		{
 			name:         "hardlink",
 			oldBase:      filepath.Join("origin", "subdir"),