cmd: support generating index in JSON format

This adds support for generating the repository index file in JSON
format using the `--json` flag. The index itself is still written
to `index.yaml`, which is fully backwards compatible as YAML is a
superset of JSON.

For big indexes (think multiple megabytes), this approach is however
more efficient in combination with the changes to the load logic,
as it prevents a YAML -> JSON roundtrip during decoding.

Signed-off-by: Hidde Beydals <hidde@hhh.computer>

cmd/helm/repo_index.go

@@ -43,6 +43,7 @@ type repoIndexOptions struct {
 	dir   string
 	url   string
 	merge string
+	json  bool
 }
 
 func newRepoIndexCmd(out io.Writer) *cobra.Command {
@@ -70,6 +71,7 @@ func newRepoIndexCmd(out io.Writer) *cobra.Command {
 	f := cmd.Flags()
 	f.StringVar(&o.url, "url", "", "url of chart repository")
 	f.StringVar(&o.merge, "merge", "", "merge the generated index into the given index")
+	f.BoolVar(&o.json, "json", false, "output in JSON format")
 
 	return cmd
 }
@@ -80,10 +82,10 @@ func (i *repoIndexOptions) run(out io.Writer) error {
 		return err
 	}
 
-	return index(path, i.url, i.merge)
+	return index(path, i.url, i.merge, i.json)
 }
 
-func index(dir, url, mergeTo string) error {
+func index(dir, url, mergeTo string, json bool) error {
 	out := filepath.Join(dir, "index.yaml")
 
 	i, err := repo.IndexDirectory(dir, url)
@@ -95,7 +97,7 @@ func index(dir, url, mergeTo string) error {
 		var i2 *repo.IndexFile
 		if _, err := os.Stat(mergeTo); os.IsNotExist(err) {
 			i2 = repo.NewIndexFile()
-			i2.WriteFile(mergeTo, 0644)
+			writeIndexFile(i2, mergeTo, json)
 		} else {
 			i2, err = repo.LoadIndexFile(mergeTo)
 			if err != nil {
@@ -105,5 +107,12 @@ func index(dir, url, mergeTo string) error {
 		i.Merge(i2)
 	}
 	i.SortEntries()
+	return writeIndexFile(i, out, json)
+}
+
+func writeIndexFile(i *repo.IndexFile, out string, json bool) error {
+	if json {
+		return i.WriteJSONFile(out, 0644)
+	}
 	return i.WriteFile(out, 0644)
 }

cmd/helm/repo_index_test.go

@@ -18,6 +18,7 @@ package main
 
 import (
 	"bytes"
+	"encoding/json"
 	"io"
 	"os"
 	"path/filepath"
@@ -68,6 +69,28 @@ func TestRepoIndexCmd(t *testing.T) {
 		t.Errorf("expected %q, got %q", expectedVersion, vs[0].Version)
 	}
 
+	b, err := os.ReadFile(destIndex)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if json.Valid(b) {
+		t.Error("did not expect index file to be valid json")
+	}
+
+	// Test with `--json`
+
+	c.ParseFlags([]string{"--json", "true"})
+	if err := c.RunE(c, []string{dir}); err != nil {
+		t.Error(err)
+	}
+
+	if b, err = os.ReadFile(destIndex); err != nil {
+		t.Fatal(err)
+	}
+	if !json.Valid(b) {
+		t.Error("index file is not valid json")
+	}
+
 	// Test with `--merge`
 
 	// Remove first two charts.

pkg/repo/index.go

@@ -233,6 +233,18 @@ func (i IndexFile) WriteFile(dest string, mode os.FileMode) error {
 	return fileutil.AtomicWriteFile(dest, bytes.NewReader(b), mode)
 }
 
+// WriteJSONFile writes an index file in JSON format to the given destination
+// path.
+//
+// The mode on the file is set to 'mode'.
+func (i IndexFile) WriteJSONFile(dest string, mode os.FileMode) error {
+	b, err := json.MarshalIndent(i, "", "  ")
+	if err != nil {
+		return err
+	}
+	return fileutil.AtomicWriteFile(dest, bytes.NewReader(b), mode)
+}
+
 // Merge merges the given index file into this index.
 //
 // This merges by name and version.

pkg/repo/index_test.go

@@ -19,6 +19,7 @@ package repo
 import (
 	"bufio"
 	"bytes"
+	"encoding/json"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -553,6 +554,27 @@ func TestIndexWrite(t *testing.T) {
 	}
 }
 
+func TestIndexJSONWrite(t *testing.T) {
+	i := NewIndexFile()
+	if err := i.MustAdd(&chart.Metadata{APIVersion: "v2", Name: "clipper", Version: "0.1.0"}, "clipper-0.1.0.tgz", "http://example.com/charts", "sha256:1234567890"); err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	dir := t.TempDir()
+	testpath := filepath.Join(dir, "test")
+	i.WriteJSONFile(testpath, 0600)
+
+	got, err := os.ReadFile(testpath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !json.Valid(got) {
+		t.Fatal("Index files doesn't contain valid JSON")
+	}
+	if !strings.Contains(string(got), "clipper-0.1.0.tgz") {
+		t.Fatal("Index files doesn't contain expected content")
+	}
+}
+
 func TestAddFileIndexEntriesNil(t *testing.T) {
 	i := NewIndexFile()
 	i.APIVersion = chart.APIVersionV1