Create and document diff package.

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
+}