cmd/config: Add examples and tutorials for config functions

- Add examples under `functions`
- Add built-in tutorial for functions

functions/examples/validator-resource-requests/image/Dockerfile

@@ -0,0 +1,15 @@
+# Copyright 2019 The Kubernetes Authors.
+# SPDX-License-Identifier: Apache-2.0
+
+FROM golang:1.13-stretch
+ENV CGO_ENABLED=0
+WORKDIR /go/src/
+COPY go.mod .
+COPY go.sum .
+RUN go mod download
+COPY main.go .
+RUN go build -v -o /usr/local/bin/config-function ./
+
+FROM alpine:latest
+COPY --from=0 /usr/local/bin/config-function /usr/local/bin/config-function
+CMD ["config-function"]

functions/examples/validator-resource-requests/image/go.mod

@@ -0,0 +1,5 @@
+module sigs.k8s.io/kustomize/functions/examples/validator-resource-requests
+
+go 1.13
+
+require sigs.k8s.io/kustomize/kyaml v0.0.0-20191126155111-73fb32c85ad4

functions/examples/validator-resource-requests/image/go.sum

@@ -0,0 +1,27 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-errors/errors v1.0.1 h1:LUHzmkK3GUKUrL/1gfBUxAHzcev3apQlezX/+O7ma6w=
+github.com/go-errors/errors v1.0.1/go.mod h1:f4zRHt4oKfwPJE5k8C9vpYG+aDHdBFUsgrm6/TyX73Q=
+github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/xlab/treeprint v0.0.0-20181112141820-a009c3971eca h1:1CFlNzQhALwjS9mBAUkycX616GzgsuYUOCHA5+HSlXI=
+github.com/xlab/treeprint v0.0.0-20181112141820-a009c3971eca/go.mod h1:ce1O1j6UtZfjr22oyGxGLbauSBp2YVXpARAosm7dHBg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.2.4 h1:/eiJrUcujPVeJ3xlSWaiNi3uSVmDGBK1pDHUHAnao1I=
+gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0-20191026110619-0b21df46bc1d h1:LCPbGQ34PMrwad11aMZ+dbz5SAsq/0ySjRwQ8I9Qwd8=
+gopkg.in/yaml.v3 v3.0.0-20191026110619-0b21df46bc1d/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+sigs.k8s.io/kustomize/kyaml v0.0.0-20191126155111-73fb32c85ad4 h1:QfQuib3Xi0uyHUi/R5MgWmDScb5iy/+LjoaGIdpmMpE=
+sigs.k8s.io/kustomize/kyaml v0.0.0-20191126155111-73fb32c85ad4/go.mod h1:rywm/rcR5LmCBghz9956tE45OdUPChFoXVVs+WmhMTI=

functions/examples/validator-resource-requests/image/main.go

@@ -0,0 +1,94 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package main implements a validator function run by `kustomize config run-fns`
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"sigs.k8s.io/kustomize/kyaml/kio"
+	"sigs.k8s.io/kustomize/kyaml/kio/kioutil"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+func main() {
+	rw := &kio.ByteReadWriter{Reader: os.Stdin, Writer: os.Stdout, KeepReaderAnnotations: true}
+	p := kio.Pipeline{
+		Inputs:  []kio.Reader{rw},       // read the inputs into a slice
+		Filters: []kio.Filter{filter{}}, // run the filter against the inputs
+		Outputs: []kio.Writer{rw}}       // copy the inputs to the output
+	if err := p.Execute(); err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(1)
+	}
+}
+
+// filter implements kio.Filter
+type filter struct{}
+
+// Filter checks each input and ensures that all containers have cpu and memory
+// reservations set, otherwise it returns an error.
+func (filter) Filter(in []*yaml.RNode) ([]*yaml.RNode, error) {
+	// validate each Resource
+	for _, r := range in {
+		if err := validate(r); err != nil {
+			return nil, err
+		}
+	}
+	return in, nil
+}
+
+func validate(r *yaml.RNode) error {
+	meta, err := r.GetMeta()
+	if err != nil {
+		return err
+	}
+
+	// lookup the containers field in the Resource
+	containers, err := r.Pipe(yaml.Lookup("spec", "template", "spec", "containers"))
+	if err != nil {
+		s, _ := r.String()
+		return fmt.Errorf("%v: %s", err, s)
+	}
+	if containers == nil {
+		// doesn't have containers, ignore it
+		return nil
+	}
+
+	// visit each container in the list and validate
+	return containers.VisitElements(func(node *yaml.RNode) error {
+
+		// check cpu is non-nil
+		f, err := node.Pipe(yaml.Lookup("resources", "requests", "cpu"))
+		if err != nil {
+			s, _ := r.String()
+			return fmt.Errorf("%v: %s", err, s)
+		}
+		if f == nil {
+			return fmt.Errorf(
+				"cpu-requests missing for a container in %s %s (%s [%s])",
+				meta.Kind, meta.Name,
+				meta.Annotations[kioutil.PathAnnotation],
+				meta.Annotations[kioutil.IndexAnnotation])
+		}
+
+		// check memory is non-nil
+		f, err = node.Pipe(yaml.Lookup("resources", "requests", "memory"))
+		if err != nil {
+			s, _ := r.String()
+			return fmt.Errorf("%v: %s", err, s)
+		}
+		if f == nil {
+			return fmt.Errorf(
+				"memory-requests missing for a container in %s in %s (%s [%s])",
+				meta.Kind, meta.Name,
+				meta.Annotations[kioutil.PathAnnotation],
+				meta.Annotations[kioutil.IndexAnnotation])
+		}
+
+		// container is valid
+		return nil
+	})
+}