contrib: Revert "Merge pull request #367 from jzelinskie/analyze-layers-v2"

This reverts commit e639367a30, reversing
changes made to f3848d9726. Issue involved
the docker history command providing missing fs layers that were not in
the saved image. Revert commit to using the manifest file again.

contrib/analyze-local-images/main.go

@@ -154,7 +154,10 @@ func AnalyzeLocalImage(imageName string, minSeverity types.Priority, endpoint, m
 
 	// Retrieve history.
 	log.Println("Retrieving image history")
-	layerIDs, err := historyFromCommand(imageName)
+	layerIDs, err := historyFromManifest(tmpPath)
+	if err != nil {
+		layerIDs, err = historyFromCommand(imageName)
+	}
 	if err != nil || len(layerIDs) == 0 {
 		return fmt.Errorf("Could not get image's history: %s", err)
 	}
@@ -269,7 +272,7 @@ func AnalyzeLocalImage(imageName string, minSeverity types.Priority, endpoint, m
 		fmt.Printf("%s No vulnerabilities matching the minimum severity level were detected in your image\n", color.YellowString("NOTE:"))
 	} else {
 		return fmt.Errorf("A total of %d vulnerabilities have been detected in your image", len(vulnerabilities))
-	}
+        }
 
 	return nil
 }
@@ -306,6 +309,33 @@ func save(imageName, path string) error {
 	return nil
 }
 
+func historyFromManifest(path string) ([]string, error) {
+	mf, err := os.Open(path + "/manifest.json")
+	if err != nil {
+		return nil, err
+	}
+	defer mf.Close()
+
+	// https://github.com/docker/docker/blob/master/image/tarexport/tarexport.go#L17
+	type manifestItem struct {
+		Config   string
+		RepoTags []string
+		Layers   []string
+	}
+
+	var manifest []manifestItem
+	if err = json.NewDecoder(mf).Decode(&manifest); err != nil {
+		return nil, err
+	} else if len(manifest) != 1 {
+		return nil, err
+	}
+	var layers []string
+	for _, layer := range manifest[0].Layers {
+		layers = append(layers, strings.TrimSuffix(layer, "/layer.tar"))
+	}
+	return layers, nil
+}
+
 func historyFromCommand(imageName string) ([]string, error) {
 	var stderr bytes.Buffer
 	cmd := exec.Command("docker", "history", "-q", "--no-trunc", imageName)