feat(cmd): support chaining multiple post-renderers

Allow --post-renderer to be specified multiple times to chain
post-renderers together. Each renderer's output is piped into the
next in the order specified. The --post-renderer-args flag now
applies to the most recently specified --post-renderer.

Signed-off-by: David Otto <ottodavid@gmx.net>

pkg/cmd/flags.go

@@ -184,88 +184,123 @@ func (o *outputValue) Set(s string) error {
 	return nil
 }
 
-// TODO there is probably a better way to pass cobra settings than as a param
 func bindPostRenderFlag(cmd *cobra.Command, varRef *postrenderer.PostRenderer, settings *cli.EnvSettings) {
-	p := &postRendererOptions{varRef, "", []string{}, settings}
-	cmd.Flags().Var(&postRendererString{p}, postRenderFlag, "the name of a postrenderer type plugin to be used for post rendering. If it exists, the plugin will be used")
-	cmd.Flags().Var(&postRendererArgsSlice{p}, postRenderArgsFlag, "an argument to the post-renderer (can specify multiple)")
+	o := &postRendererChainOptions{renderer: varRef, settings: settings}
+	cmd.Flags().Var(&postRendererNameFlag{o}, postRenderFlag, "the name of a postrenderer type plugin to be used for post rendering. If it exists, the plugin will be used. Can be specified multiple times to chain post-renderers; each renderer's output is piped into the next")
+	cmd.Flags().Var(&postRendererArgsFlag{o}, postRenderArgsFlag, "an argument to the post-renderer (can specify multiple). Applies to the most recently specified --post-renderer flag")
 }
 
 type postRendererOptions struct {
-	renderer   *postrenderer.PostRenderer
 	pluginName string
 	args       []string
-	settings   *cli.EnvSettings
 }
 
-type postRendererString struct {
-	options *postRendererOptions
+type postRendererChainOptions struct {
+	renderer      *postrenderer.PostRenderer
+	postRenderers []*postRendererOptions
+	settings      *cli.EnvSettings
 }
 
-func (p *postRendererString) String() string {
-	return p.options.pluginName
+func (o *postRendererChainOptions) rebuildRendererChain() error {
+	renderers := make([]postrenderer.PostRenderer, 0, len(o.postRenderers))
+	for _, e := range o.postRenderers {
+		renderer, err := postrenderer.NewPostRendererPlugin(o.settings, e.pluginName, e.args...)
+		if err != nil {
+			return err
+		}
+		renderers = append(renderers, renderer)
+	}
+
+	*o.renderer = postrenderer.NewChain(renderers...)
+	return nil
+}
+
+type postRendererNameFlag struct {
+	postRendererChainOptions *postRendererChainOptions
+}
+
+func (p *postRendererNameFlag) String() string {
+	names := make([]string, 0, len(p.postRendererChainOptions.postRenderers))
+	for _, renderer := range p.postRendererChainOptions.postRenderers {
+		names = append(names, renderer.pluginName)
+	}
+	return strings.Join(names, ",")
 }
 
-func (p *postRendererString) Type() string {
-	return "postRendererString"
+func (p *postRendererNameFlag) Type() string {
+	return "string"
 }
 
-func (p *postRendererString) Set(val string) error {
+func (p *postRendererNameFlag) Set(val string) error {
 	if val == "" {
 		return nil
 	}
-	if p.options.pluginName != "" {
-		return errors.New("cannot specify --post-renderer flag more than once")
-	}
-	p.options.pluginName = val
-	pr, err := postrenderer.NewPostRendererPlugin(p.options.settings, p.options.pluginName, p.options.args...)
-	if err != nil {
-		return err
-	}
-	*p.options.renderer = pr
-	return nil
+	p.postRendererChainOptions.postRenderers = append(p.postRendererChainOptions.postRenderers, &postRendererOptions{pluginName: val})
+	err := p.postRendererChainOptions.rebuildRendererChain()
+	return err
 }
 
-type postRendererArgsSlice struct {
-	options *postRendererOptions
+type postRendererArgsFlag struct {
+	options *postRendererChainOptions
 }
 
-func (p *postRendererArgsSlice) String() string {
-	return "[" + strings.Join(p.options.args, ",") + "]"
+// lastRenderer returns the most recently specified --post-renderer entry, to
+// which --post-renderer-args values are applied.
+func (p *postRendererArgsFlag) lastRenderer() (*postRendererOptions, error) {
+	if len(p.options.postRenderers) == 0 {
+		return nil, errors.New("--post-renderer-args must follow a --post-renderer flag")
+	}
+	return p.options.postRenderers[len(p.options.postRenderers)-1], nil
 }
 
-func (p *postRendererArgsSlice) Type() string {
-	return "postRendererArgsSlice"
+func (p *postRendererArgsFlag) String() string {
+	renderer, err := p.lastRenderer()
+	if err != nil {
+		return "[]"
+	}
+	return "[" + strings.Join(renderer.args, ",") + "]"
 }
 
-func (p *postRendererArgsSlice) Set(val string) error {
-	// a post-renderer defined by a user may accept empty arguments
-	p.options.args = append(p.options.args, val)
+func (p *postRendererArgsFlag) Type() string {
+	return "args"
+}
 
-	if p.options.pluginName == "" {
-		return nil
-	}
-	// overwrite if already create PostRenderer by `post-renderer` flags
-	pr, err := postrenderer.NewPostRendererPlugin(p.options.settings, p.options.pluginName, p.options.args...)
+func (p *postRendererArgsFlag) Set(val string) error {
+	renderer, err := p.lastRenderer()
 	if err != nil {
 		return err
 	}
-	*p.options.renderer = pr
-	return nil
+
+	renderer.args = append(renderer.args, val)
+
+	err = p.options.rebuildRendererChain()
+	return err
 }
 
-func (p *postRendererArgsSlice) Append(val string) error {
-	p.options.args = append(p.options.args, val)
+func (p *postRendererArgsFlag) Append(val string) error {
+	renderer, err := p.lastRenderer()
+	if err != nil {
+		return err
+	}
+	renderer.args = append(renderer.args, val)
 	return nil
 }
 
-func (p *postRendererArgsSlice) Replace(val []string) error {
-	p.options.args = val
+func (p *postRendererArgsFlag) Replace(val []string) error {
+	renderer, err := p.lastRenderer()
+	if err != nil {
+		return err
+	}
+	renderer.args = val
 	return nil
 }
 
-func (p *postRendererArgsSlice) GetSlice() []string {
-	return p.options.args
+func (p *postRendererArgsFlag) GetSlice() []string {
+	renderer, err := p.lastRenderer()
+	if err != nil {
+		return nil
+	}
+	return renderer.args
 }
 
 func compVersionFlag(chartRef string, _ string) ([]string, cobra.ShellCompDirective) {

pkg/cmd/flags_test.go

@@ -17,7 +17,9 @@ limitations under the License.
 package cmd
 
 import (
+	"bytes"
 	"fmt"
+	"runtime"
 	"testing"
 	"time"
 
@@ -25,6 +27,7 @@ import (
 
 	"helm.sh/helm/v4/pkg/action"
 	chart "helm.sh/helm/v4/pkg/chart/v2"
+	"helm.sh/helm/v4/pkg/postrenderer"
 	"helm.sh/helm/v4/pkg/release/common"
 	release "helm.sh/helm/v4/pkg/release/v1"
 )
@@ -99,22 +102,68 @@ func outputFlagCompletionTest(t *testing.T, cmdName string) {
 	runTestCmd(t, tests)
 }
 
-func TestPostRendererFlagSetOnce(t *testing.T) {
+func TestPostRendererFlagAllowsMultiple(t *testing.T) {
 	cfg := action.Configuration{}
 	client := action.NewInstall(&cfg)
 	settings.PluginsDirectory = "testdata/helmhome/helm/plugins"
-	str := postRendererString{
-		options: &postRendererOptions{
+	str := postRendererNameFlag{
+		postRendererChainOptions: &postRendererChainOptions{
 			renderer: &client.PostRenderer,
 			settings: settings,
 		},
 	}
-	// Set the plugin name once
+	// Setting the plugin name once is ok
 	require.NoError(t, str.Set("postrenderer-v1"))
+	require.NotNil(t, client.PostRenderer)
 
-	// Set the plugin name again to the same value is not ok
-	require.Error(t, str.Set("postrenderer-v1"))
+	// Setting a second plugin name chains it after the first
+	require.NoError(t, str.Set("postrenderer-v1-second"))
+	require.NotNil(t, client.PostRenderer)
+	require.IsType(t, &postrenderer.Chain{}, client.PostRenderer)
+}
+
+func TestPostRendererArgs_WithoutPrecedingRendererErrors(t *testing.T) {
+	cfg := action.Configuration{}
+	client := action.NewInstall(&cfg)
+	settings.PluginsDirectory = "testdata/helmhome/helm/plugins"
+	args := postRendererArgsFlag{
+		options: &postRendererChainOptions{
+			renderer: &client.PostRenderer,
+			settings: settings,
+		},
+	}
+	require.Error(t, args.Set("ARG1"))
+}
+
+func TestPostRendererChain_RunsInOrder(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("skipping on windows: test uses a sed-based plugin")
+	}
+	cfg := action.Configuration{}
+	client := action.NewInstall(&cfg)
+	settings.PluginsDirectory = "testdata/helmhome/helm/plugins"
+
+	options := &postRendererChainOptions{
+		renderer: &client.PostRenderer,
+		settings: settings,
+	}
+	str := postRendererNameFlag{postRendererChainOptions: options}
+	argsFlag := postRendererArgsFlag{options: options}
+
+	// First renderer: FOOTEST -> BARTEST
+	require.NoError(t, str.Set("postrenderer-v1"))
+	// Second renderer: BARTEST -> BAZTEST
+	require.NoError(t, str.Set("postrenderer-v1-second"))
+
+	require.NotNil(t, client.PostRenderer)
+
+	out, err := client.PostRenderer.Run(bytes.NewBufferString("FOOTEST"))
+	require.NoError(t, err)
+	require.Contains(t, out.String(), "BAZTEST")
 
-	// Set the plugin name again to a different value is not ok
-	require.Error(t, str.Set("cat"))
+	// Args apply to the most recently added renderer (the second one)
+	require.NoError(t, argsFlag.Set("CUSTOM"))
+	out, err = client.PostRenderer.Run(bytes.NewBufferString("FOOTEST"))
+	require.NoError(t, err)
+	require.Contains(t, out.String(), "CUSTOM")
 }

pkg/cmd/testdata/helmhome/helm/plugins/postrenderer-v1-second/plugin.yaml

@@ -0,0 +1,8 @@
+apiVersion: v1
+name: "postrenderer-v1-second"
+version: "1.2.3"
+type: postrenderer/v1
+runtime: subprocess
+runtimeConfig:
+  platformCommand:
+  - command: "${HELM_PLUGIN_DIR}/sed-test.sh"

pkg/cmd/testdata/helmhome/helm/plugins/postrenderer-v1-second/sed-test.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+if [ $# -eq 0 ]; then
+  sed s/BARTEST/BAZTEST/g <&0
+else
+  sed s/BARTEST/"$*"/g <&0
+fi

pkg/postrenderer/chain.go

@@ -0,0 +1,48 @@
+/*
+Copyright The Helm 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 postrenderer
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// Chain is a PostRenderer that runs a sequence of PostRenderers, feeding the
+// output of each renderer as the input to the next. This allows multiple
+// post-renderer plugins to be composed into a single pipeline.
+type Chain struct {
+	renderers []PostRenderer
+}
+
+// NewChain creates a Chain that will run the given renderers in order. An
+// empty chain is valid and behaves as a no-op renderer that returns its
+// input unchanged.
+func NewChain(renderers ...PostRenderer) *Chain {
+	return &Chain{renderers: renderers}
+}
+
+func (c *Chain) Run(renderedManifests *bytes.Buffer) (*bytes.Buffer, error) {
+	manifests := renderedManifests
+	for i, renderer := range c.renderers {
+		var err error
+		manifests, err = renderer.Run(manifests)
+		if err != nil {
+			return nil, fmt.Errorf("post-renderer %d/%d failed: %w", i+1, len(c.renderers), err)
+		}
+	}
+	return manifests, nil
+}

pkg/postrenderer/chain_test.go

@@ -0,0 +1,79 @@
+/*
+Copyright The Helm 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 postrenderer
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// fakeRenderer is a simple PostRenderer used for chain testing. It appends
+// its suffix to the input, or returns an error if configured to fail.
+type fakeRenderer struct {
+	suffix  string
+	failErr error
+}
+
+func (f *fakeRenderer) Run(renderedManifests *bytes.Buffer) (*bytes.Buffer, error) {
+	if f.failErr != nil {
+		return nil, f.failErr
+	}
+	out := bytes.NewBufferString(renderedManifests.String() + f.suffix)
+	return out, nil
+}
+
+func TestChain_Empty(t *testing.T) {
+	c := NewChain()
+	out, err := c.Run(bytes.NewBufferString("hello"))
+	require.NoError(t, err)
+	assert.Equal(t, "hello", out.String())
+}
+
+func TestChain_Single(t *testing.T) {
+	c := NewChain(&fakeRenderer{suffix: "-a"})
+	out, err := c.Run(bytes.NewBufferString("hello"))
+	require.NoError(t, err)
+	assert.Equal(t, "hello-a", out.String())
+}
+
+func TestChain_Multiple_OrderPreserved(t *testing.T) {
+	c := NewChain(
+		&fakeRenderer{suffix: "-a"},
+		&fakeRenderer{suffix: "-b"},
+		&fakeRenderer{suffix: "-c"},
+	)
+	out, err := c.Run(bytes.NewBufferString("hello"))
+	require.NoError(t, err)
+	assert.Equal(t, "hello-a-b-c", out.String())
+}
+
+func TestChain_ErrorStopsPipeline(t *testing.T) {
+	boom := errors.New("boom")
+	c := NewChain(
+		&fakeRenderer{suffix: "-a"},
+		&fakeRenderer{failErr: boom},
+		&fakeRenderer{suffix: "-c"},
+	)
+	out, err := c.Run(bytes.NewBufferString("hello"))
+	require.Error(t, err)
+	assert.Nil(t, out)
+	assert.ErrorIs(t, err, boom)
+}