implement post-renderer for dependencies

resolves #13536

e.g.

dependencies:
- name: nginx
  version: "1.2.3"
  repository: "https://example.com/charts
  postRenderer:
    command: ytt
    args:
      - "--file"
      - "overlays/nginx/overlay.yaml"
      - "--file"
      - "-"

Signed-off-by: Raymond Augé <rayauge@doublebite.com>

pkg/chart/dependency.go

@@ -17,6 +17,11 @@ package chart
 
 import "time"
 
+type PostRendererOptions struct {
+	Command string   `json:"command" yaml:"command"`
+	Args    []string `json:"args,omitempty" yaml:"args,omitempty"`
+}
+
 // Dependency describes a chart upon which another chart depends.
 //
 // Dependencies can be used to express developer intent, or to capture the state
@@ -47,6 +52,8 @@ type Dependency struct {
 	ImportValues []interface{} `json:"import-values,omitempty" yaml:"import-values,omitempty"`
 	// Alias usable alias to be used for the chart
 	Alias string `json:"alias,omitempty" yaml:"alias,omitempty"`
+	// A post rendering operation that will be applied to the rendered outputs of this dependency
+	PostRenderer *PostRendererOptions `json:"postRenderer,omitempty" yaml:"postRenderer,omitempty"`
 }
 
 // Validate checks for common problems with the dependency datastructure in

pkg/engine/engine.go

@@ -17,6 +17,7 @@ limitations under the License.
 package engine
 
 import (
+	"bytes"
 	"fmt"
 	"log"
 	"path"
@@ -31,6 +32,7 @@ import (
 
 	"helm.sh/helm/v3/pkg/chart"
 	"helm.sh/helm/v3/pkg/chartutil"
+	"helm.sh/helm/v3/pkg/postrender"
 )
 
 // Engine is an implementation of the Helm rendering implementation for templates.
@@ -75,7 +77,11 @@ func New(config *rest.Config) Engine {
 // bar chart during render time.
 func (e Engine) Render(chrt *chart.Chart, values chartutil.Values) (map[string]string, error) {
 	tmap := allTemplates(chrt, values)
-	return e.render(tmap)
+	rendered, err := e.render(tmap)
+	if err != nil {
+		return nil, err
+	}
+	return postRenderDependency(nil, chrt, rendered)
 }
 
 // Render takes a chart, optional values, and value overrides, and attempts to
@@ -307,6 +313,77 @@ func (e Engine) render(tpls map[string]renderable) (rendered map[string]string,
 	return rendered, nil
 }
 
+func postRenderDependency(parent *chart.Chart, chrt *chart.Chart, rendered map[string]string) (map[string]string, error) {
+	for _, c := range chrt.Dependencies() {
+		_, err := postRenderDependency(chrt, c, rendered)
+
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// Skip root chart since it has it's own post-render mechanism
+	if chrt.IsRoot() || parent == nil {
+		return rendered, nil
+	}
+
+	var postRenderOptions *chart.PostRendererOptions
+
+	for _, depMetadata := range parent.Metadata.Dependencies {
+		if depMetadata.Name == chrt.Name() {
+			postRenderOptions = depMetadata.PostRenderer
+			break
+		}
+	}
+
+	if postRenderOptions == nil {
+		return rendered, nil
+	}
+
+	postRenderer, err := postrender.NewExec(postRenderOptions.Command, postRenderOptions.Args...)
+
+	if err != nil {
+		errorMessage := err.Error()
+		if strings.HasPrefix(errorMessage, "unable to find binary at ") {
+			log.Printf("[INFO] Skipping dependency post render operation because: %s", errorMessage)
+
+			return rendered, nil
+		}
+
+		return nil, err
+	}
+
+	fullChartPath := chrt.ChartFullPath()
+
+	for k, renderedContent := range rendered {
+		if len(strings.TrimSpace(renderedContent)) == 0 || strings.HasSuffix(k, "/templates/NOTES.txt") {
+			continue
+		}
+
+		if strings.HasPrefix(k, fullChartPath+"/templates/") {
+			result, err := postRender(postRenderer, renderedContent)
+
+			if err != nil {
+				return nil, err
+			}
+
+			rendered[k] = result
+		}
+	}
+
+	return rendered, nil
+}
+
+func postRender(postRenderer postrender.PostRenderer, renderedContent string) (string, error) {
+	var buffer bytes.Buffer
+	buffer.WriteString(renderedContent)
+	newBuffer, err := postRenderer.Run(&buffer)
+	if err != nil {
+		return "", err
+	}
+	return newBuffer.String(), nil
+}
+
 func cleanupParseError(filename string, err error) error {
 	tokens := strings.Split(err.Error(), ": ")
 	if len(tokens) == 1 {

pkg/engine/engine_test.go

@@ -18,12 +18,14 @@ package engine
 
 import (
 	"fmt"
+	"os"
 	"path"
 	"strings"
 	"sync"
 	"testing"
 	"text/template"
 
+	"github.com/stretchr/testify/assert"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
@@ -1300,3 +1302,76 @@ func TestRenderTplMissingKeyString(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestRenderDependencyPostRenderer(t *testing.T) {
+	dep := &chart.Chart{
+		Metadata: &chart.Metadata{
+			Name: "foo",
+		},
+		Templates: []*chart.File{
+			{Name: "templates/foo1", Data: []byte("value: {{ add .Values.bar 2 }}\n")},
+			{Name: "templates/NOTES.txt", Data: []byte("SOME TEXT")},
+			{Name: "templates/empty", Data: []byte("")},
+		},
+		Values: map[string]interface{}{},
+	}
+
+	cwd, _ := os.Getwd()
+
+	c := &chart.Chart{
+		Metadata: &chart.Metadata{
+			Name:    "moby",
+			Version: "1.2.3",
+			Dependencies: []*chart.Dependency{
+				{
+					Name: "foo",
+					PostRenderer: &chart.PostRendererOptions{
+						Command: cwd + "/../../testdata/postrender.sh",
+					},
+				},
+			},
+		},
+		Templates: []*chart.File{
+			{Name: "templates/test1", Data: []byte("name: {{ .Chart.Name }}")},
+		},
+		Values: map[string]interface{}{},
+	}
+
+	c.SetDependencies(dep)
+
+	vals := map[string]interface{}{
+		"Values": map[string]any{
+			"foo": map[string]any{
+				"bar": 3,
+			},
+		},
+	}
+
+	v, err := chartutil.CoalesceValues(c, vals)
+	if err != nil {
+		t.Fatalf("Failed to coalesce values: %s", err)
+	}
+
+	var e Engine
+	out, err := e.Render(c, v)
+	if err != nil {
+		t.Errorf("Failed to render templates: %s", err)
+		return
+	}
+
+	assert.Equal(t, len(out), 4)
+
+	expected := "name: moby"
+
+	fp := path.Join(c.ChartFullPath(), "templates/test1")
+	if out[fp] != expected {
+		t.Errorf("Expected %q, got %q", expected, out[fp])
+	}
+
+	expected = "value: 25\n"
+
+	fp = path.Join(dep.ChartFullPath(), "templates/foo1")
+	if out[fp] != expected {
+		t.Errorf("Expected %q, got %q", expected, out[fp])
+	}
+}

testdata/postrender.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+s=$(tee | sed 's/5/25/')
+
+echo "${s}"