Add Starlark kio.Filter

- Support for implementing filters in Starlark

kyaml/starlark/example_test.go

@@ -0,0 +1,93 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package starlark_test
+
+import (
+	"bytes"
+	"fmt"
+	"log"
+
+	"sigs.k8s.io/kustomize/kyaml/kio"
+	"sigs.k8s.io/kustomize/kyaml/starlark"
+)
+
+func ExampleFilter_Filter() {
+	// input contains the items that will provided to the starlark program
+	input := bytes.NewBufferString(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: deployment-1
+spec:
+  template:
+    spec:
+      containers:
+      - name: nginx
+        image: nginx:1.8.1 # {"$ref": "#/definitions/io.k8s.cli.substitutions.image-1"}
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: deployment-2
+spec:
+  template:
+    spec:
+      containers:
+      - name: nginx
+        image: nginx:1.7.9 # {"$ref": "#/definitions/io.k8s.cli.substitutions.image-2"}
+`)
+
+	// fltr transforms the input using a starlark program
+	fltr := &starlark.Filter{
+		Name: "annotate",
+		Program: `
+def run(items):
+  for item in items:
+    item["metadata"]["annotations"]["foo"] = "bar"
+
+run(resourceList["items"])
+`,
+	}
+
+	// output contains the transformed resources
+	output := &bytes.Buffer{}
+
+	// run the fltr against the inputs using a kio.Pipeline
+	err := kio.Pipeline{
+		Inputs:  []kio.Reader{&kio.ByteReader{Reader: input}},
+		Filters: []kio.Filter{fltr},
+		Outputs: []kio.Writer{&kio.ByteWriter{Writer: output}}}.Execute()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(output.String())
+
+	// Output:
+	// apiVersion: apps/v1
+	// kind: Deployment
+	// metadata:
+	//   name: deployment-1
+	//   annotations:
+	//     foo: bar
+	// spec:
+	//   template:
+	//     spec:
+	//       containers:
+	//       - name: nginx
+	//         image: nginx:1.8.1 # {"$ref": "#/definitions/io.k8s.cli.substitutions.image-1"}
+	//---
+	// apiVersion: apps/v1
+	// kind: Deployment
+	// metadata:
+	//   name: deployment-2
+	//   annotations:
+	//     foo: bar
+	// spec:
+	//   template:
+	//     spec:
+	//       containers:
+	//       - name: nginx
+	//         image: nginx:1.7.9 # {"$ref": "#/definitions/io.k8s.cli.substitutions.image-2"}
+}