feat(chart_downloader): Use cached chart if possible in chart_downloader.go

Signed-off-by: Suleiman Dibirov <idsulik@gmail.com>

pkg/downloader/chart_downloader.go

@@ -99,20 +99,25 @@ func (c *ChartDownloader) DownloadTo(ref, version, dest string) (string, *proven
 
 	c.Options = append(c.Options, getter.WithAcceptHeader("application/gzip,application/octet-stream"))
 
-	data, err := g.Get(u.String(), c.Options...)
-	if err != nil {
-		return "", nil, err
-	}
-
 	name := filepath.Base(u.Path)
+
 	if u.Scheme == registry.OCIScheme {
 		idx := strings.LastIndexByte(name, ':')
 		name = fmt.Sprintf("%s-%s.tgz", name[:idx], name[idx+1:])
 	}
 
 	destfile := filepath.Join(dest, name)
-	if err := fileutil.AtomicWriteFile(destfile, data, 0644); err != nil {
-		return destfile, nil, err
+
+	// If the file does not exist locally, fetch it from the remote source.
+	if _, err := os.Stat(destfile); err != nil {
+		data, err := g.Get(u.String(), c.Options...)
+		if err != nil {
+			return "", nil, err
+		}
+
+		if err := fileutil.AtomicWriteFile(destfile, data, 0644); err != nil {
+			return destfile, nil, err
+		}
 	}
 
 	// If provenance is requested, verify it.

pkg/downloader/chart_downloader_test.go

@@ -197,7 +197,8 @@ func TestDownloadTo(t *testing.T) {
 		},
 	}
 	cname := "/signtest-0.1.0.tgz"
-	dest := srv.Root()
+	dest := filepath.Join(srv.Root(), "signtest")
+	os.MkdirAll(dest, 0755)
 	where, v, err := c.DownloadTo(srv.URL()+cname, "", dest)
 	if err != nil {
 		t.Fatal(err)
@@ -216,6 +217,35 @@ func TestDownloadTo(t *testing.T) {
 	}
 }
 
+func TestDownloadToWithCachedChart(t *testing.T) {
+	c := ChartDownloader{
+		Out:              os.Stderr,
+		Verify:           VerifyNever,
+		Keyring:          "testdata/helm-test-key.pub",
+		RepositoryConfig: repoConfig,
+		RepositoryCache:  repoCache,
+		Getters: getter.All(&cli.EnvSettings{
+			RepositoryConfig: repoConfig,
+			RepositoryCache:  repoCache,
+		}),
+	}
+	dest := t.TempDir()
+	cname := "signtest-0.1.0.tgz"
+	os.Create(filepath.Join(dest, cname))
+	where, _, err := c.DownloadTo("https://localhost/"+cname, "", dest)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if expect := filepath.Join(dest, cname); where != expect {
+		t.Errorf("Expected download to %s, got %s", expect, where)
+	}
+
+	if _, err := os.Stat(filepath.Join(dest, cname)); err != nil {
+		t.Error(err)
+	}
+}
+
 func TestDownloadTo_TLS(t *testing.T) {
 	// Set up mock server w/ tls enabled
 	srv, err := repotest.NewTempServerWithCleanup(t, "testdata/*.tgz*")
@@ -248,7 +278,8 @@ func TestDownloadTo_TLS(t *testing.T) {
 		Options: []getter.Option{},
 	}
 	cname := "test/signtest"
-	dest := srv.Root()
+	dest := filepath.Join(srv.Root(), "signtest")
+	os.MkdirAll(dest, 0755)
 	where, v, err := c.DownloadTo(cname, "", dest)
 	if err != nil {
 		t.Fatal(err)