Unexport layout.WriteLayer; Implement suggested changes for validat…

…eLayers and temp file naming

pkg/v1/layout/write.go

@@ -16,8 +16,6 @@ package layout
 
 import (
 	"bytes"
-	"crypto/rand"
-	"encoding/hex"
 	"encoding/json"
 	"io"
 	"io/ioutil"
@@ -238,11 +236,12 @@ func (l Path) writeBlob(hash v1.Hash, size int64, r io.ReadCloser, renamer func(
 		return nil
 	}
 
-	// If a rename func was provided, use a temporary file suffix
+	// If a renamer func was provided write to a temporary file
+	open := func() (*os.File, error) { return os.Create(file) }
 	if renamer != nil {
-		file += ".tmp"
+		open = func() (*os.File, error) { return ioutil.TempFile(dir, hash.Hex) }
 	}
-	w, err := os.Create(file)
+	w, err := open()
 	if err != nil {
 		return err
 	}
@@ -256,31 +255,30 @@ func (l Path) writeBlob(hash v1.Hash, size int64, r io.ReadCloser, renamer func(
 	if err != nil {
 		return err
 	}
+	renamePath := l.path("blobs", finalHash.Algorithm, finalHash.Hex)
+
 	// Always close file before renaming
 	if err := w.Close(); err != nil {
 		return err
 	}
-	return os.Rename(file, l.path("blobs", finalHash.Algorithm, finalHash.Hex))
+	return os.Rename(w.Name(), renamePath)
 }
 
-// WriteLayer writes the compressed layer to a blob. Unlike WriteBlob it will
+// writeLayer writes the compressed layer to a blob. Unlike WriteBlob it will
 // write to a temporary file (suffixed with .tmp) within the layout until the
 // compressed reader is fully consumed and written to disk. Also unlike
 // WriteBlob, it will not skip writing and exit without error when a blob file
 // exists, but does not have the correct size. (The blob hash is not
 // considered, because it may be expensive to compute.)
-func (l Path) WriteLayer(layer v1.Layer) error {
+func (l Path) writeLayer(layer v1.Layer) error {
 	d, err := layer.Digest()
 	if err != nil {
 		// Allow digest errors, since streams may not have calculated the hash
-		// yet. Instead, use a random value for the digest and require it to be
+		// yet. Instead, use an empty value, which will be transformed into a
+		// random file name with `ioutil.TempFile` and the final digest will be
 		// calculated after writing to a temp file and before renaming to the
 		// final path.
-		var randHash [32]byte
-		if _, err := rand.Read(randHash[:]); err != nil {
-			return err
-		}
-		d = v1.Hash{Algorithm: "sha256", Hex: hex.EncodeToString(randHash[:])}
+		d = v1.Hash{Algorithm: "sha256", Hex: ""}
 	}
 
 	s, err := layer.Size()
@@ -332,7 +330,7 @@ func (l Path) WriteImage(img v1.Image) error {
 	for _, layer := range layers {
 		layer := layer
 		g.Go(func() error {
-			return l.WriteLayer(layer)
+			return l.writeLayer(layer)
 		})
 	}
 	if err := g.Wait(); err != nil {

pkg/v1/layout/write_test.go

@@ -627,7 +627,7 @@ func TestOverwriteWithWriteLayer(t *testing.T) {
 	}
 
 	// try writing expected contents with WriteLayer
-	if err := l.WriteLayer(layer); err != nil {
+	if err := l.writeLayer(layer); err != nil {
 		t.Fatalf("error attempting to overwrite truncated layer with valid layer; (Path).WriteLayer = %v", err)
 	}
 

pkg/v1/validate/image.go

@@ -114,23 +114,20 @@ func validateLayers(img v1.Image, opt ...Option) error {
 		return layersExist(layers)
 	}
 
-	cf, err := img.ConfigFile()
-	if err != nil {
-		return err
-	}
-
-	m, err := img.Manifest()
-	if err != nil {
-		return err
-	}
-
 	digests := []v1.Hash{}
 	diffids := []v1.Hash{}
 	udiffids := []v1.Hash{}
 	sizes := []int64{}
 	for i, layer := range layers {
 		cl, err := computeLayer(layer)
 		if errors.Is(err, io.ErrUnexpectedEOF) {
+			// Errored while reading tar content of layer because a header or
+			// content section was not the correct length. This is most likely
+			// due to an incomplete download or otherwise interrupted process.
+			m, err := img.Manifest()
+			if err != nil {
+				return fmt.Errorf("undersized layer[%d] content", i)
+			}
 			return fmt.Errorf("undersized layer[%d] content: Manifest.Layers[%d].Size=%d", i, i, m.Layers[i].Size)
 		}
 		if err != nil {
@@ -144,6 +141,16 @@ func validateLayers(img v1.Image, opt ...Option) error {
 		sizes = append(sizes, cl.size)
 	}
 
+	cf, err := img.ConfigFile()
+	if err != nil {
+		return err
+	}
+
+	m, err := img.Manifest()
+	if err != nil {
+		return err
+	}
+
 	errs := []string{}
 	for i, layer := range layers {
 		digest, err := layer.Digest()