bugfix: walk function exit incorrectly

image/config.go

@@ -53,9 +53,9 @@ func findConfig(w walker, d *descriptor) (*config, error) {
 	var c config
 	cpath := filepath.Join("blobs", d.normalizeDigest())
 
-	if err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
+	switch err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
 		if info.IsDir() || filepath.Clean(path) != cpath {
-			return fmt.Errorf("%s: config not found", cpath)
+			return nil
 		}
 		buf, err := ioutil.ReadAll(r)
 		if err != nil {
@@ -69,12 +69,15 @@ func findConfig(w walker, d *descriptor) (*config, error) {
 		if err := json.Unmarshal(buf, &c); err != nil {
 			return err
 		}
-
-		return nil
-	}); err != nil {
+		return errEOW
+	}); err {
+	case nil:
+		return nil, fmt.Errorf("%s: config not found", cpath)
+	case errEOW:
+		return &c, nil
+	default:
 		return nil, err
 	}
-	return &c, nil
 }
 
 func (c *config) runtimeSpec(rootfs string) (*specs.Spec, error) {

image/descriptor.go

@@ -41,44 +41,49 @@ func findDescriptor(w walker, name string) (*descriptor, error) {
 	var d descriptor
 	dpath := filepath.Join("refs", name)
 
-	if err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
+	switch err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
 		if info.IsDir() || filepath.Clean(path) != dpath {
-			return fmt.Errorf("%s: descriptor not found", dpath)
+			return nil
 		}
 
 		if err := json.NewDecoder(r).Decode(&d); err != nil {
 			return err
 		}
 
-		return nil
-	}); err != nil {
+		return errEOW
+	}); err {
+	case nil:
+		return nil, fmt.Errorf("%s: descriptor not found", dpath)
+	case errEOW:
+		return &d, nil
+	default:
 		return nil, err
 	}
-
-	return &d, nil
 }
 
 func (d *descriptor) validate(w walker) error {
-	if err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
+	switch err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
 		if info.IsDir() {
-			return fmt.Errorf("%s: not found", d.normalizeDigest())
+			return nil
 		}
 
 		digest, err := filepath.Rel("blobs", filepath.Clean(path))
 		if err != nil || d.normalizeDigest() != digest {
-			return fmt.Errorf("%s: not found", d.normalizeDigest())
+			return nil
 		}
 
 		if err := d.validateContent(r); err != nil {
 			return err
 		}
-
+		return errEOW
+	}); err {
+	case nil:
+		return fmt.Errorf("%s: not found", d.normalizeDigest())
+	case errEOW:
 		return nil
-	}); err != nil {
+	default:
 		return errors.Wrapf(err, "%s: validation failed", d.normalizeDigest())
 	}
-
-	return nil
 }
 
 func (d *descriptor) validateContent(r io.Reader) error {

image/manifest.go

@@ -40,9 +40,9 @@ func findManifest(w walker, d *descriptor) (*manifest, error) {
 	var m manifest
 	mpath := filepath.Join("blobs", d.normalizeDigest())
 
-	if err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
+	switch err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
 		if info.IsDir() || filepath.Clean(path) != mpath {
-			return fmt.Errorf("%s: manifest not found", mpath)
+			return nil
 		}
 
 		buf, err := ioutil.ReadAll(r)
@@ -62,12 +62,15 @@ func findManifest(w walker, d *descriptor) (*manifest, error) {
 			return fmt.Errorf("%s: no layers found", path)
 		}
 
-		return nil
-	}); err != nil {
+		return errEOW
+	}); err {
+	case nil:
+		return nil, fmt.Errorf("%s: manifest not found", mpath)
+	case errEOW:
+		return &m, nil
+	default:
 		return nil, err
 	}
-
-	return &m, nil
 }
 
 func (m *manifest) validate(w walker) error {
@@ -90,26 +93,30 @@ func (m *manifest) unpack(w walker, dest string) error {
 			continue
 		}
 
-		if err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
+		switch err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
 			if info.IsDir() {
-				return fmt.Errorf("%s: blob digest not found", d.normalizeDigest())
+				return nil
 			}
 
 			dd, err := filepath.Rel("blobs", filepath.Clean(path))
 			if err != nil || d.normalizeDigest() != dd {
-				return fmt.Errorf("%s: blob digest not found", d.normalizeDigest())
+				return nil
 			}
 
 			if err := unpackLayer(dest, r); err != nil {
 				return errors.Wrap(err, "error extracting layer")
 			}
 
+			return errEOW
+		}); err {
+		case nil:
+			return fmt.Errorf("%s: layer not found", dest)
+		case errEOW:
 			return nil
-		}); err != nil {
+		default:
 			return err
 		}
 	}
-
 	return nil
 }
 

image/walker.go

@@ -16,13 +16,18 @@ package image
 
 import (
 	"archive/tar"
+	"fmt"
 	"io"
 	"os"
 	"path/filepath"
 
 	"github.com/pkg/errors"
 )
 
+var (
+	errEOW = fmt.Errorf("end of walk") // error to signal stop walking
+)
+
 // walkFunc is a function type that gets called for each file or directory visited by the Walker.
 type walkFunc func(path string, _ os.FileInfo, _ io.Reader) error