Add Cached function for files already Download

This will return any files already in the cache,
with valid digest, but not download any new ones.

Signed-off-by: Anders F Björklund <[email protected]>

Author: afbjorklund

pkg/downloader/downloader.go

@@ -242,6 +242,38 @@ func Download(local, remote string, opts ...Opt) (*Result, error) {
 	return res, nil
 }
 
+func Cached(remote string, opts ...Opt) (string, error) {
+	var o options
+	for _, f := range opts {
+		if err := f(&o); err != nil {
+			return "", err
+		}
+	}
+	if o.cacheDir == "" {
+		return "", fmt.Errorf("caching-only mode requires the cache directory to be specified")
+	}
+
+	shad := cacheDirectoryPath(o.cacheDir, remote)
+	shadData := filepath.Join(shad, "data")
+	shadDigest, err := cacheDigestPath(shad, o.expectedDigest)
+	if err != nil {
+		return "", err
+	}
+	if _, err := os.Stat(shadData); err != nil {
+		return "", err
+	}
+	if _, err := os.Stat(shadDigest); err != nil {
+		if err := validateCachedDigest(shadDigest, o.expectedDigest); err != nil {
+			return "", err
+		}
+	} else {
+		if err := validateLocalFileDigest(shadData, o.expectedDigest); err != nil {
+			return "", err
+		}
+	}
+	return shadData, nil
+}
+
 // cacheDirectoryPath returns the cache subdirectory path.
 // - "url" file contains the url
 // - "data" file contains the data

pkg/downloader/downloader_test.go

@@ -5,6 +5,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"strings"
 	"testing"
 
 	"github.com/opencontainers/go-digest"
@@ -87,6 +88,23 @@ func TestDownloadRemote(t *testing.T) {
 		assert.NilError(t, err)
 		assert.Equal(t, StatusUsedCache, r.Status)
 	})
+	t.Run("cached", func(t *testing.T) {
+		_, err := Download("", dummyRemoteFileURL, WithExpectedDigest(dummyRemoteFileDigest))
+		assert.ErrorContains(t, err, "cache directory to be specified")
+
+		cacheDir := filepath.Join(t.TempDir(), "cache")
+		r, err := Download("", dummyRemoteFileURL, WithExpectedDigest(dummyRemoteFileDigest), WithCacheDir(cacheDir))
+		assert.NilError(t, err)
+		assert.Equal(t, StatusDownloaded, r.Status)
+
+		p, err := Cached(dummyRemoteFileURL, WithExpectedDigest(dummyRemoteFileDigest), WithCacheDir(cacheDir))
+		assert.NilError(t, err)
+		assert.Assert(t, strings.HasPrefix(p, cacheDir), "expected %s to be in %s", p, cacheDir)
+
+		wrongDigest := digest.Digest("sha256:8313944efb4f38570c689813f288058b674ea6c487017a5a4738dc674b65f9d9")
+		_, err = Cached(dummyRemoteFileURL, WithExpectedDigest(wrongDigest), WithCacheDir(cacheDir))
+		assert.ErrorContains(t, err, "expected digest")
+	})
 }
 
 func TestDownloadLocal(t *testing.T) {