Merge pull request #70 from liangchenye/read-manifest

contrib: load image history from 'manifest.json'

contrib/analyze-local-images/main.go

@@ -72,7 +72,10 @@ func main() {
 
 	// Retrieve history
 	fmt.Println("Getting image's history")
-	layerIDs, err := history(imageName)
+	layerIDs, err := historyFromManifest(path)
+	if err != nil {
+		layerIDs, err = historyFromCommand(imageName)
+	}
 	if err != nil || len(layerIDs) == 0 {
 		log.Fatalf("- Could not get image's history: %s\n", err)
 	}
@@ -168,7 +171,34 @@ func save(imageName string) (string, error) {
 	return path, nil
 }
 
-func history(imageName string) ([]string, error) {
+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)
 	cmd.Stderr = &stderr