Create and document diff package.

pkg/diff/rundiff.go

@@ -0,0 +1,63 @@
+package diff
+
+import (
+	"github.com/ghodss/yaml"
+
+	"io"
+
+	"github.com/kubernetes-sigs/kustomize/pkg/resource"
+)
+
+// RunDiff runs system diff program to compare two ResourceCollections.
+func RunDiff(raw, transformed resource.ResourceCollection,
+	out, errOut io.Writer) error {
+	transformedDir, err := writeYamlToNewDir(transformed, "transformed")
+	if err != nil {
+		return err
+	}
+	defer transformedDir.delete()
+
+	noopDir, err := writeYamlToNewDir(raw, "noop")
+	if err != nil {
+		return err
+	}
+	defer noopDir.delete()
+
+	return newProgram(out, errOut).run(noopDir.name(), transformedDir.name())
+}
+
+// writeYamlToNewDir writes each obj in ResourceCollection to a file in a new directory.
+// The directory's name will begin with the given prefix.
+// Each file is named with GroupVersionKindName.
+func writeYamlToNewDir(in resource.ResourceCollection, prefix string) (*directory, error) {
+	dir, err := newDirectory(prefix)
+	if err != nil {
+		return nil, err
+	}
+
+	for gvkn, obj := range in {
+		f, err := dir.newFile(gvkn.String())
+		if err != nil {
+			return nil, err
+		}
+		err = print(obj.Data, f)
+		f.Close()
+		if err != nil {
+			return nil, err
+		}
+	}
+	return dir, nil
+}
+
+// Print the object as YAML.
+func print(obj interface{}, w io.Writer) error {
+	if obj == nil {
+		return nil
+	}
+	data, err := yaml.Marshal(obj)
+	if err != nil {
+		return err
+	}
+	_, err = w.Write(data)
+	return err
+}