contrib: Fix analyze_local_images when image has missing layers

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)