first prototype

Signed-off-by: Holger Metschulat <holger.metschulat@telekom.de>

internal/resolver/resolver.go

@@ -123,7 +123,7 @@ func (r *Resolver) Resolve(reqs []*chart.Dependency, repoNames map[string]string
 		var ok bool
 		found := true
 		if !registry.IsOCI(d.Repository) {
-			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)
 			}

pkg/downloader/chart_downloader.go

@@ -356,7 +356,7 @@ 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')")
 		}

pkg/downloader/manager.go

@@ -824,7 +824,7 @@ 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
 		}

pkg/repo/index.go

@@ -25,6 +25,7 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/Masterminds/semver/v3"
@@ -115,6 +116,30 @@ 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 {