Normalize archive member names.

src/extract.go

@@ -11,6 +11,7 @@ import (
 	"io"
 	"math"
 	"os"
+	"path"
 	"strings"
 
 	"github.com/c2h5oh/datasize"
@@ -61,6 +62,16 @@ func (err UnresolvedRefError) Error() string {
 	return fmt.Sprintf("%d unresolved blob references", len(err.missing))
 }
 
+func normalizeArchiveMemberName(fileName string) string {
+	// Strip the leading slash and any extraneous path segments.
+	fileName = path.Clean(fileName)
+	fileName = strings.TrimPrefix(fileName, "/")
+	if fileName == "." {
+		fileName = ""
+	}
+	return fileName
+}
+
 // Returns a map of git hash to entry. If `manifest` is nil, returns an empty map.
 func indexManifestByGitHash(manifest *Manifest) map[string]*Entry {
 	index := map[string]*Entry{}
@@ -110,15 +121,10 @@ func ExtractTar(ctx context.Context, reader io.Reader, oldManifest *Manifest) (*
 			return nil, err
 		}
 
-		// For some reason, GNU tar includes any leading `.` path segments in archive filenames,
-		// unless there is a `..` path segment anywhere in the input filenames.
-		fileName := header.Name
-		for {
-			if strippedName, found := strings.CutPrefix(fileName, "./"); found {
-				fileName = strippedName
-			} else {
-				break
-			}
+		fileName := normalizeArchiveMemberName(header.Name)
+		if fileName == "" {
+			// This must be the root directory. It will be filled in by EnsureLeadingDirectories.
+			continue
 		}
 
 		switch header.Typeflag {
@@ -200,8 +206,9 @@ func ExtractZip(ctx context.Context, reader io.Reader, oldManifest *Manifest) (*
 	missing := []string{}
 	manifest := NewManifest()
 	for _, file := range archive.File {
+		normalizedName := normalizeArchiveMemberName(file.Name)
 		if strings.HasSuffix(file.Name, "/") {
-			AddDirectory(manifest, file.Name)
+			AddDirectory(manifest, normalizedName)
 		} else {
 			fileReader, err := file.Open()
 			if err != nil {
@@ -216,10 +223,10 @@ func ExtractZip(ctx context.Context, reader io.Reader, oldManifest *Manifest) (*
 
 			if file.Mode()&os.ModeSymlink != 0 {
 				entry := addSymlinkOrBlobReference(
-					manifest, file.Name, string(fileData), index, &missing)
+					manifest, normalizedName, string(fileData), index, &missing)
 				dataBytesRecycled += entry.GetOriginalSize()
 			} else {
-				AddFile(manifest, file.Name, fileData)
+				AddFile(manifest, normalizedName, fileData)
 				dataBytesTransferred += int64(len(fileData))
 			}
 		}
@@ -240,4 +247,3 @@ func ExtractZip(ctx context.Context, reader io.Reader, oldManifest *Manifest) (*
 
 	return manifest, nil
 }
-

src/manifest.go

@@ -151,6 +151,9 @@ func AddProblem(manifest *Manifest, pathName, format string, args ...any) error
 func EnsureLeadingDirectories(manifest *Manifest) {
 	for name := range manifest.Contents {
 		for dir := path.Dir(name); dir != "." && dir != ""; dir = path.Dir(dir) {
+			if dir == "/" {
+				panic("malformed manifest (paths must not be rooted in /)")
+			}
 			if _, exists := manifest.Contents[dir]; !exists {
 				AddDirectory(manifest, dir)
 			}

src/patch.go

@@ -70,7 +70,7 @@ func ApplyTarPatch(manifest *Manifest, reader io.Reader, parents CreateParentsMo
 			return err
 		}
 
-		segments := strings.Split(strings.TrimRight(header.Name, "/"), "/")
+		segments := strings.Split(normalizeArchiveMemberName(header.Name), "/")
 		fileName := segments[len(segments)-1]
 		node := root
 		for index, segment := range segments[:len(segments)-1] {