Implement StripComponents to zip

cmd/arc/main.go

@@ -263,6 +263,7 @@ func getFormat(subcommand string) (interface{}, error) {
 		v.MkdirAll = mkdirAll
 		v.SelectiveCompression = selectiveCompression
 		v.ImplicitTopLevelFolder = implicitTopLevelFolder
+		v.StripComponents = stripComponents
 		v.ContinueOnError = continueOnError
 	case *archiver.Gz:
 		v.CompressionLevel = compressionLevel

zip.go

@@ -70,6 +70,10 @@ type Zip struct {
 	// especially on extraction.
 	ImplicitTopLevelFolder bool
 
+	// Strip number of leading paths. This feature is available
+	// only during unpacking of the entire archive.
+	StripComponents int
+
 	// If true, errors encountered during reading
 	// or writing a single file will be logged and
 	// the operation will continue on remaining files.
@@ -243,19 +247,30 @@ func (z *Zip) extractNext(to string) error {
 	}
 	defer f.Close()
 
-	errPath := z.CheckPath(to, f.Header.(zip.FileHeader).Name)
+	header, ok := f.Header.(zip.FileHeader)
+	if !ok {
+		return fmt.Errorf("expected header to be zip.FileHeader but was %T", f.Header)
+	}
+
+	errPath := z.CheckPath(to, header.Name)
 	if errPath != nil {
 		return fmt.Errorf("checking path traversal attempt: %v", errPath)
 	}
-	return z.extractFile(f, to)
-}
 
-func (z *Zip) extractFile(f File, to string) error {
-	header, ok := f.Header.(zip.FileHeader)
-	if !ok {
-		return fmt.Errorf("expected header to be zip.FileHeader but was %T", f.Header)
+	if z.StripComponents > 0 {
+		if strings.Count(header.Name, "/") < z.StripComponents {
+			return nil // skip path with fewer components
+		}
+
+		for i := 0; i < z.StripComponents; i++ {
+			slash := strings.Index(header.Name, "/")
+			header.Name = header.Name[slash+1:]
+		}
 	}
+	return z.extractFile(f, to, &header)
+}
 
+func (z *Zip) extractFile(f File, to string, header *zip.FileHeader) error {
 	to = filepath.Join(to, header.Name)
 
 	// if a directory, no content; simply make the directory and return
@@ -583,7 +598,7 @@ func (z *Zip) Extract(source, target, destination string) error {
 			}
 			joined := filepath.Join(destination, end)
 
-			err = z.extractFile(f, joined)
+			err = z.extractFile(f, joined, &zfh)
 			if err != nil {
 				return fmt.Errorf("extracting file %s: %v", zfh.Name, err)
 			}