Add custom error type for layer not found

This avoids the need for the lifecycle to do some brittle string checking

Signed-off-by: Natalie Arellano <narellano@vmware.com>

cnb_image.go

@@ -82,6 +82,17 @@ func (i *CNBImageCore) GetAnnotateRefName() (string, error) {
 }
 
 func (i *CNBImageCore) GetLayer(diffID string) (io.ReadCloser, error) {
+ layerHash, err := v1.NewHash(diffID)
+ if err != nil {
+ return nil, err
+ }
+ configFile, err := i.ConfigFile()
+ if err != nil {
+ return nil, err
+ }
+ if !contains(configFile.RootFS.DiffIDs, layerHash) {
+ return nil, ErrLayerNotFound{DiffID: layerHash.String()}
+ }
  hash, err := v1.NewHash(diffID)
  if err != nil {
  return nil, err
@@ -93,6 +104,15 @@ func (i *CNBImageCore) GetLayer(diffID string) (io.ReadCloser, error) {
  return layer.Uncompressed()
 }
 
+func contains(diffIDs []v1.Hash, hash v1.Hash) bool {
+ for _, diffID := range diffIDs {
+ if diffID.String() == hash.String() {
+ return true
+ }
+ }
+ return false
+}
+
 // TBD Deprecated: History
 func (i *CNBImageCore) History() ([]v1.History, error) {
  configFile, err := getConfigFile(i.Image)

image.go

@@ -100,3 +100,11 @@ func (e SaveError) Error() string {
  }
  return fmt.Sprintf("failed to write image to the following tags: %s", strings.Join(errors, ","))
 }
+
+type ErrLayerNotFound struct {
+ DiffID string
+}
+
+func (e ErrLayerNotFound) Error() string {
+ return fmt.Sprintf("failed to find layer with diff ID %q", e.DiffID)
+}

local/local.go

@@ -53,6 +53,13 @@ func (i *Image) GetLayer(diffID string) (io.ReadCloser, error) {
  if err != nil {
  return nil, err
  }
+ configFile, err := i.ConfigFile()
+ if err != nil {
+ return nil, err
+ }
+ if !contains(configFile.RootFS.DiffIDs, layerHash) {
+ return nil, imgutil.ErrLayerNotFound{DiffID: layerHash.String()}
+ }
  layer, err := i.LayerByDiffID(layerHash)
  if err == nil {
  // this avoids downloading ALL the image layers from the daemon
@@ -62,13 +69,6 @@ func (i *Image) GetLayer(diffID string) (io.ReadCloser, error) {
  return layer.Uncompressed()
  }
  }
- configFile, err := i.ConfigFile()
- if err != nil {
- return nil, err
- }
- if !contains(configFile.RootFS.DiffIDs, layerHash) {
- return nil, fmt.Errorf("image %q does not contain layer with diff ID %q", i.Name(), layerHash.String())
- }
  if err = i.ensureLayers(); err != nil {
  return nil, err
  }