From b24920ef9d57fc0fb28781046ecfb12d0720eafc Mon Sep 17 00:00:00 2001
From: Holger Metschulat <holger.metschulat@telekom.de>
Date: Sat, 26 Jun 2021 00:03:30 +0200
Subject: [PATCH] first prototype

Signed-off-by: Holger Metschulat <holger.metschulat@telekom.de>
---
 internal/resolver/resolver.go      |  2 +-
 pkg/downloader/chart_downloader.go |  2 +-
 pkg/downloader/manager.go          |  2 +-
 pkg/repo/index.go                  | 25 +++++++++++++++++++++++++
 4 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/internal/resolver/resolver.go b/internal/resolver/resolver.go
index de0634093..0d07ba953 100644
--- a/internal/resolver/resolver.go
+++ b/internal/resolver/resolver.go
@@ -113,7 +113,7 @@ func (r *Resolver) Resolve(reqs []*chart.Dependency, repoNames map[string]string
 		var ok bool
 		found := true
 		if !strings.HasPrefix(d.Repository, "oci://") {
-			repoIndex, err := repo.LoadIndexFile(filepath.Join(r.cachepath, helmpath.CacheIndexFile(repoName)))
+			repoIndex, err := repo.LoadIndexFileWithCaching(filepath.Join(r.cachepath, helmpath.CacheIndexFile(repoName)))
 			if err != nil {
 				return nil, errors.Wrapf(err, "no cached repository for %s found. (try 'helm repo update')", repoName)
 			}
diff --git a/pkg/downloader/chart_downloader.go b/pkg/downloader/chart_downloader.go
index 2c0d55a55..7ccf36f88 100644
--- a/pkg/downloader/chart_downloader.go
+++ b/pkg/downloader/chart_downloader.go
@@ -351,7 +351,7 @@ func (c *ChartDownloader) scanReposForURL(u string, rf *repo.File) (*repo.Entry,
 		}
 
 		idxFile := filepath.Join(c.RepositoryCache, helmpath.CacheIndexFile(r.Config.Name))
-		i, err := repo.LoadIndexFile(idxFile)
+		i, err := repo.LoadIndexFileWithCaching(idxFile)
 		if err != nil {
 			return nil, errors.Wrap(err, "no cached repo found. (try 'helm repo update')")
 		}
diff --git a/pkg/downloader/manager.go b/pkg/downloader/manager.go
index ff5f9c4e7..879984dc4 100644
--- a/pkg/downloader/manager.go
+++ b/pkg/downloader/manager.go
@@ -803,7 +803,7 @@ func (m *Manager) loadChartRepositories() (map[string]*repo.ChartRepository, err
 	for _, re := range rf.Repositories {
 		lname := re.Name
 		idxFile := filepath.Join(m.RepositoryCache, helmpath.CacheIndexFile(lname))
-		index, err := repo.LoadIndexFile(idxFile)
+		index, err := repo.LoadIndexFileWithCaching(idxFile)
 		if err != nil {
 			return indices, err
 		}
diff --git a/pkg/repo/index.go b/pkg/repo/index.go
index e86b17349..a9c5620b8 100644
--- a/pkg/repo/index.go
+++ b/pkg/repo/index.go
@@ -25,6 +25,7 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/Masterminds/semver/v3"
@@ -113,6 +114,30 @@ func LoadIndexFile(path string) (*IndexFile, error) {
 	return i, nil
 }
 
+var cache = make(map[string]*IndexFile)
+var cacheLock sync.RWMutex
+
+func LoadIndexFileWithCaching(path string) (*IndexFile, error) {
+	// if already in cache, return cached entry
+	cacheLock.RLock()
+	if idx, ok := cache[path]; ok {
+		cacheLock.RUnlock()
+		// safe to return a pointer to the cached entry here since once in cache
+		// entry will never be overwritten
+		return idx, nil
+	}
+	cacheLock.RUnlock()
+	// not in cache, need to load from disk
+	idx, err := LoadIndexFile(path)
+	if err == nil {
+		// we fetched the index successfully. Store it in cache.
+		cacheLock.Lock()
+		cache[path] = idx
+		cacheLock.Unlock()
+	}
+	return idx, err
+}
+
 // MustAdd adds a file to the index
 // This can leave the index in an unsorted state
 func (i IndexFile) MustAdd(md *chart.Metadata, filename, baseURL, digest string) error {