image: heal stale metis cache entries

pkg/image/download.go

@@ -27,38 +27,37 @@ func DownloadAndVerify(url, dest, checksum string) (string, error) {
 	}
 	if strings.HasSuffix(url, ".xz") {
 		archive := dest + ".xz"
-		if _, err := os.Stat(archive); errors.Is(err, os.ErrNotExist) {
+		if err := ensureVerifiedFile(url, archive, checksum); err != nil {
-			if err := downloadRaw(url, archive); err != nil {
-				return "", err
-			}
-		} else if err != nil {
 			return "", err
 		}
-		if err := VerifyChecksum(archive, checksum); err != nil {
+		if err := decompressXZ(archive, dest); err != nil {
-			return "", err
-		}
-		if _, err := os.Stat(dest); errors.Is(err, os.ErrNotExist) {
-			if err := decompressXZ(archive, dest); err != nil {
-				return "", err
-			}
-		} else if err != nil {
 			return "", err
 		}
 		return dest, nil
 	}
-	if _, err := os.Stat(dest); errors.Is(err, os.ErrNotExist) {
+	if err := ensureVerifiedFile(url, dest, checksum); err != nil {
-		if err := downloadRaw(url, dest); err != nil {
-			return "", err
-		}
-	} else if err != nil {
-		return "", err
-	}
-	if err := VerifyChecksum(dest, checksum); err != nil {
 		return "", err
 	}
 	return dest, nil
 }
 
+func ensureVerifiedFile(url, dest, checksum string) error {
+	if _, err := os.Stat(dest); err == nil {
+		if err := VerifyChecksum(dest, checksum); err == nil || checksum == "" {
+			return nil
+		}
+		if removeErr := os.Remove(dest); removeErr != nil && !errors.Is(removeErr, os.ErrNotExist) {
+			return removeErr
+		}
+	} else if !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	if err := downloadRaw(url, dest); err != nil {
+		return err
+	}
+	return VerifyChecksum(dest, checksum)
+}
+
 func downloadRaw(url, dest string) error {
 	if strings.HasPrefix(url, "file://") {
 		src := strings.TrimPrefix(url, "file://")

pkg/image/download_test.go

@@ -71,3 +71,39 @@ func TestDownloadAndVerifyUsesArchiveChecksumForXZ(t *testing.T) {
 		t.Fatalf("unexpected decompressed content: %q", string(data))
 	}
 }
+
+func TestDownloadAndVerifyReplacesStaleBadArchiveCache(t *testing.T) {
+	if _, err := exec.LookPath("xz"); err != nil {
+		t.Skip("xz not available")
+	}
+	dir := t.TempDir()
+	raw := filepath.Join(dir, "base.img")
+	if err := os.WriteFile(raw, []byte("metis-xz-test"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	compressed := raw + ".xz"
+	cmd := exec.Command("xz", "-zk", raw)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("xz: %v: %s", err, string(out))
+	}
+	archiveBytes, err := os.ReadFile(compressed)
+	if err != nil {
+		t.Fatalf("ReadFile archive: %v", err)
+	}
+	archiveSum := sha256.Sum256(archiveBytes)
+	dest := filepath.Join(dir, "copy.img")
+	staleArchive := dest + ".xz"
+	if err := os.WriteFile(staleArchive, []byte("bad-cache"), 0o644); err != nil {
+		t.Fatalf("WriteFile stale archive: %v", err)
+	}
+	if _, err := DownloadAndVerify("file://"+compressed, dest, "sha256:"+hex.EncodeToString(archiveSum[:])); err != nil {
+		t.Fatalf("DownloadAndVerify with stale archive: %v", err)
+	}
+	data, err := os.ReadFile(dest)
+	if err != nil {
+		t.Fatalf("ReadFile dest: %v", err)
+	}
+	if string(data) != "metis-xz-test" {
+		t.Fatalf("unexpected decompressed content: %q", string(data))
+	}
+}