Create and document diff package.

pkg/diff/directory.go

@@ -0,0 +1,38 @@
+package diff
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// directory represents a new temp directory and lets one create files in it.
+type directory struct {
+	n string
+}
+
+// newDirectory makes a directory instance holding a new temp directory on disk.
+// The directory name is the given prefix following by a random string.
+func newDirectory(prefix string) (*directory, error) {
+	name, err := ioutil.TempDir("", prefix+"-")
+	if err != nil {
+		return nil, err
+	}
+
+	return &directory{n: name}, nil
+}
+
+// newFile creates a new file in the directory.
+func (d *directory) newFile(name string) (*os.File, error) {
+	return os.OpenFile(filepath.Join(d.n, name), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0700)
+}
+
+// delete removes the directory recursively.
+func (d *directory) delete() error {
+	return os.RemoveAll(d.n)
+}
+
+// name is the name of the directory.
+func (d *directory) name() string {
+	return d.n
+}

pkg/diff/doc.go

@@ -0,0 +1,2 @@
+// Package diff runs system diff to compare resource collections
+package diff

pkg/diff/program.go

@@ -0,0 +1,59 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package diff
+
+import (
+	"io"
+	"os"
+
+	"k8s.io/utils/exec"
+)
+
+// program wraps the system diff program.
+// If specified, the value of KUBERNETES_EXTERNAL_DIFF environment variable
+// will be used instead of simply `diff(1)`.
+type program struct {
+	stdout io.Writer
+	stderr io.Writer
+}
+
+func newProgram(out, errOut io.Writer) *program {
+	return &program{
+		stdout: out,
+		stderr: errOut,
+	}
+}
+
+func (d *program) makeCommand(args ...string) exec.Cmd {
+	diff := ""
+	if envDiff := os.Getenv("KUBERNETES_EXTERNAL_DIFF"); envDiff != "" {
+		diff = envDiff
+	} else {
+		diff = "diff"
+		args = append([]string{"-u", "-N"}, args...)
+	}
+	cmd := exec.New().Command(diff, args...)
+	cmd.SetStdout(d.stdout)
+	cmd.SetStderr(d.stderr)
+	return cmd
+}
+
+// run runs the detected diff program. `from` and `to` are the directory to diff.
+func (d *program) run(from, to string) error {
+	d.makeCommand(from, to).Run() // Ignore diff return code
+	return nil
+}

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
+}