Make an S3 listing the server cuts short an error (closes #297)

The SDK paginator takes a listing page marked truncated but carrying no
continuation token for the last page and stops without an error. A
server answering V2 listings V1-style sends such pages, so ListObjects
and ListObjectsStream returned the first page as the whole listing, and
prune treated the blobs of the snapshots on later pages as unreferenced.
Both now fetch each page through nextListPage, which returns
ErrNoContinuationToken for such a page; prune, snapshot list and remote
nuke already handle a listing error.

The test serves a fixed reply from a stub server, since gofakes3 always
sends the token.

Model: opus-5-5

README.md

@@ -412,8 +412,7 @@ destination store.
 entirely. Remote storage is unaffected; the next backup will do a full
 scan and re-deduplicate against existing remote blobs, and the local
 index will re-bind to the currently configured storage destination.
-Use this after changing `storage_url`, or `s3.endpoint`, `s3.bucket` or
-`s3.prefix`, to a different destination.
+Use this after changing `storage_url` to a different destination.
 * `--force`: Skip confirmation prompt
 
 ---

TODO.md

@@ -22,23 +22,14 @@ the tag exists and is exercised; what is left is merging `next` to
 
 # Completed Steps
 
-- 2026-10-13: Made a failed or interrupted backup remove the temporary
-  file of the blob it was packing
-  ([issue #302](https://git.eeqj.de/sneak/vaultik/issues/302)). When
-  `snapshot create` stopped on a file error, a full temporary directory
-  or Ctrl-C, that blob was never finalized and its `vaultik-blob-*.tmp`
-  file, up to `blob_size_limit` of encrypted data, stayed in `$TMPDIR`;
-  every such run left another. Phase 2 now removes it whenever it stops
-  before the last blob is finalized.
-
-- 2026-10-12: Bound the local index to the destination an `s3.*` config
-  names ([issue #298](https://git.eeqj.de/sneak/vaultik/issues/298)).
-  Only `storage_url` was checked, so after `s3.bucket` or `s3.prefix`
-  changed, the next backup treated every chunk as already stored,
-  uploaded nothing, and completed a snapshot that could not be restored.
-  Without `storage_url`, the local index is now bound to `s3.endpoint`,
-  `s3.bucket` and `s3.prefix`, and a change is refused as a changed
-  `storage_url` is.
+- 2026-10-13: Made an S3 listing that the server cuts short an error
+  ([issue #297](https://git.eeqj.de/sneak/vaultik/issues/297)). A page
+  marked truncated with no continuation token, as a server answering V2
+  listings V1-style sends, ended the listing without an error, so
+  `prune` saw only the snapshots on the first page and could delete
+  blobs the rest still use. Such a page is now a listing error, and
+  `prune`, `snapshot list` and `remote nuke` handle it as a destination
+  that cannot be listed.
 
 - 2026-10-12: Rejected a retention duration longer than about 292 years
   ([issue #289](https://git.eeqj.de/sneak/vaultik/issues/289)). The

internal/blob/packer.go

@@ -245,17 +245,6 @@ func (p *Packer) Flush(ctx context.Context) error {
 	return nil
 }
 
-// DiscardCurrentBlob closes and removes the temp file of the blob being
-// packed, if any, and drops that blob. A caller that stops before Flush
-// must call it, or the temp file is left behind. Thread-safe.
-func (p *Packer) DiscardCurrentBlob() {
-	p.mu.Lock()
-	defer p.mu.Unlock()
-
-	p.cleanupTempFile()
-	p.currentBlob = nil
-}
-
 // FinalizeBlob finalizes the current blob being assembled.
 // This compresses the accumulated chunks, encrypts the result, and computes
 // the content-addressed hash. The finalized blob is either passed to the

internal/s3/client.go

@@ -18,6 +18,13 @@ import (
 	"github.com/aws/smithy-go/logging"
 )
 
+// ErrNoContinuationToken is returned by ListObjects and ListObjectsStream
+// when the server marks a page of a listing truncated but sends no
+// continuation token to fetch the rest with, as a server answering V2
+// listings V1-style does.
+var ErrNoContinuationToken = errors.New(
+	"server marked the listing truncated but sent no continuation token")
+
 // Client wraps the AWS S3 client for vaultik operations.
 // It provides a simplified interface for S3 operations with automatic
 // prefix handling and connection management. All operations are performed
@@ -214,7 +221,7 @@ func (c *Client) ListObjects(ctx context.Context, prefix string) ([]string, erro
 	})
 
 	for paginator.HasMorePages() {
-		page, err := paginator.NextPage(ctx)
+		page, err := nextListPage(ctx, paginator)
 		if err != nil {
 			return nil, err
 		}
@@ -235,6 +242,26 @@ func (c *Client) ListObjects(ctx context.Context, prefix string) ([]string, erro
 	return keys, nil
 }
 
+// nextListPage fetches the next page of a listing. The SDK paginator takes
+// a page marked truncated without a continuation token for the last page
+// and stops without an error, so such a page is ErrNoContinuationToken
+// here instead.
+func nextListPage(
+	ctx context.Context, paginator *s3.ListObjectsV2Paginator,
+) (*s3.ListObjectsV2Output, error) {
+	page, err := paginator.NextPage(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	truncated := aws.ToBool(page.IsTruncated)
+	if truncated && aws.ToString(page.NextContinuationToken) == "" {
+		return nil, ErrNoContinuationToken
+	}
+
+	return page, nil
+}
+
 // HeadObject checks if an object exists in S3.
 // Returns true if the object exists, false otherwise.
 // The key is automatically prefixed with the configured prefix.
@@ -300,7 +327,7 @@ func (c *Client) ListObjectsStream(
 		})
 
 		for paginator.HasMorePages() {
-			page, err := paginator.NextPage(ctx)
+			page, err := nextListPage(ctx, paginator)
 			if err != nil {
 				ch <- ObjectInfo{Err: err}
 

internal/snapshot/scanner.go

@@ -1295,11 +1295,6 @@ func (s *Scanner) batchAddFilesToSnapshot(
 func (s *Scanner) processPhase(
 	ctx context.Context, filesToProcess []*FileToProcess, result *ScanResult,
 ) error {
-	// On an error or cancellation the blob being packed is never
-	// finalized, so its temp file must be removed here. After a
-	// successful flush there is no such blob and this does nothing.
-	defer s.packer.DiscardCurrentBlob()
-
 	// Calculate total bytes to process
 	var totalBytes int64
 	for _, f := range filesToProcess {

internal/snapshot/skip_errors_test.go

@@ -381,60 +381,3 @@ func TestScannerCancelStopsSkipErrorsRun(t *testing.T) {
 		})
 	}
 }
-
-// TestScannerRemovesBlobTempFileWhenRunStops checks that a run stopped
-// part-way, by a file it cannot read or by a cancellation, removes the
-// temp file of the blob it was packing.
-func TestScannerRemovesBlobTempFileWhenRunStops(t *testing.T) {
-	t.Parallel()
-
-	// a.txt is backed up first and starts a blob; the run stops at b.txt.
-	const target = "/source/b.txt"
-
-	tests := []struct {
-		name  string
-		newFs func(cancel context.CancelFunc) afero.Fs
-	}{
-		{
-			name: "file cannot be read",
-			newFs: func(context.CancelFunc) afero.Fs {
-				return &readFailFs{Fs: afero.NewMemMapFs(), target: target}
-			},
-		},
-		{
-			name: "cancelled",
-			newFs: func(cancel context.CancelFunc) afero.Fs {
-				return &cancelOnOpenFs{
-					Fs: afero.NewMemMapFs(), target: target, cancel: cancel,
-				}
-			},
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			t.Parallel()
-
-			ctx, cancel := context.WithCancel(context.Background())
-			defer cancel()
-
-			fs := tt.newFs(cancel)
-			writeSkipErrorTestFile(t, fs, "/source/a.txt", "first file content")
-			writeSkipErrorTestFile(t, fs, target, "second file content")
-
-			_, err := runSkipErrorScan(ctx, t, fs, "/source", false, nil)
-			if err == nil {
-				t.Fatal("expected the scan to stop with an error, got nil")
-			}
-
-			left, err := afero.Glob(fs, filepath.Join(os.TempDir(), "vaultik-blob-*"))
-			if err != nil {
-				t.Fatalf("listing blob temp files: %v", err)
-			}
-
-			if len(left) != 0 {
-				t.Fatalf("expected no blob temp file left, got %v", left)
-			}
-		})
-	}
-}

internal/storage/s3_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"slices"
@@ -22,13 +23,16 @@ import (
 // s3TestBucket is the bucket created for each in-process S3 server.
 const s3TestBucket = "test-bucket"
 
-// Credentials for the tests that build a storer from a config.Config. The
-// in-process S3 server accepts any.
+// Credentials for the tests' S3 clients. The test servers accept any.
 const (
 	s3TestAccessKeyID     = "key"
 	s3TestSecretAccessKey = "secret"
 )
 
+// s3TestRegion is the region of the S3 clients built here with
+// s3.NewClient. The test servers ignore it.
+const s3TestRegion = "us-east-1"
+
 // newS3Storer builds an s3:// backend backed by a fresh in-process
 // S3 server. It reuses the same in-memory S3 harness (gofakes3 + s3mem
 // over httptest) that internal/s3 and the not-found regression test use,
@@ -55,7 +59,7 @@ func newS3Storer(t *testing.T) storage.Storer {
 		Bucket:          s3TestBucket,
 		AccessKeyID:     "test",
 		SecretAccessKey: "test",
-		Region:          "us-east-1",
+		Region:          s3TestRegion,
 	})
 	if err != nil {
 		t.Fatalf("new client: %v", err)
@@ -93,6 +97,68 @@ func TestS3StorerMissingKeyMapsToErrNotFound(t *testing.T) {
 	}
 }
 
+// TestS3ListingCutShortIsAnError checks that List and ListStream fail on a
+// listing page marked truncated that carries no continuation token, as a
+// server answering V2 listings V1-style sends it. Taken as the last page,
+// it would hide every later key, and prune would treat the blobs of the
+// snapshots listed there as unreferenced.
+func TestS3ListingCutShortIsAnError(t *testing.T) {
+	t.Parallel()
+
+	const (
+		prefix        = "metadata/"
+		truncatedPage = `<?xml version="1.0" encoding="UTF-8"?>
+<ListBucketResult xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
+  <Name>test-bucket</Name>
+  <Prefix>metadata/</Prefix>
+  <KeyCount>1</KeyCount>
+  <MaxKeys>1</MaxKeys>
+  <IsTruncated>true</IsTruncated>
+  <Contents>
+    <Key>metadata/snap/manifest.json.zst</Key>
+    <Size>8</Size>
+  </Contents>
+</ListBucketResult>`
+	)
+
+	srv := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			_, _ = io.WriteString(w, truncatedPage)
+		}))
+	t.Cleanup(srv.Close)
+
+	client, err := s3.NewClient(context.Background(), s3.Config{
+		Endpoint:        srv.URL,
+		Bucket:          s3TestBucket,
+		AccessKeyID:     s3TestAccessKeyID,
+		SecretAccessKey: s3TestSecretAccessKey,
+		Region:          s3TestRegion,
+	})
+	if err != nil {
+		t.Fatalf("new client: %v", err)
+	}
+
+	storer := storage.NewS3Storer(client)
+	ctx := context.Background()
+
+	keys, err := storer.List(ctx, prefix)
+	if !errors.Is(err, s3.ErrNoContinuationToken) {
+		t.Errorf("List = %q, %v; want ErrNoContinuationToken", keys, err)
+	}
+
+	var streamErr error
+
+	for obj := range storer.ListStream(ctx, prefix) {
+		if obj.Err != nil {
+			streamErr = obj.Err
+		}
+	}
+
+	if !errors.Is(streamErr, s3.ErrNoContinuationToken) {
+		t.Errorf("ListStream error = %v, want ErrNoContinuationToken", streamErr)
+	}
+}
+
 // TestS3URLPrefixKeyLayout pins the bucket keys an s3:// URL reads and
 // writes: the README's remote storage layout, with the prefix joined to
 // each key by one "/". s3://b/p and s3://b/p/ must be the same

internal/vaultik/storage_bind.go

@@ -9,7 +9,7 @@ import (
 )
 
 // errStorageBindingMismatch is returned when the local index database is
-// bound to a different destination than the configured one.
+// bound to a different destination than the configured storage_url.
 var errStorageBindingMismatch = errors.New(
 	"local index is bound to a different backup destination")
 
@@ -24,9 +24,8 @@ var errStorageBindingMismatch = errors.New(
 //
 // Behaviour:
 //   - On first use (empty stored value), record the configured
-//     destination (storage_url, or the s3.* endpoint, bucket and
-//     prefix) and log the binding.
-//   - When the stored value matches the configured destination, do
+//     storage_url and log the binding.
+//   - When the stored value matches the configured storage_url, do
 //     nothing and return nil.
 //   - When the two differ, refuse with an error that tells the user
 //     how to recover (revert the config, or run `vaultik database
@@ -47,10 +46,12 @@ func (v *Vaultik) EnsureStorageBinding() error {
 
 	configured := v.Config.StorageURL
 	if configured == "" {
-		// The s3.* form: bind on its endpoint, bucket and prefix,
-		// written the way storage_url would name the same destination.
-		s3 := v.Config.S3
-		configured = "s3://" + s3.Bucket + "/" + s3.Prefix + "?endpoint=" + s3.Endpoint
+		// Some legacy configs still use the split s3.* keys instead of
+		// storage_url. Falling back to a synthetic URL for those would
+		// hide the fact that the binding is loose. Instead, treat
+		// unset as "nothing to bind against" — the check is
+		// necessarily best-effort for those configs.
+		return nil
 	}
 
 	stored, err := v.Repositories.LocalMeta.Get(v.ctx, database.LocalMetaKeyStorageURL)
@@ -95,8 +96,7 @@ func buildBindingMismatchMessage(stored, configured string) string {
 		"future snapshots referencing blobs that don't exist at the new destination.\n" +
 		"\n" +
 		"To proceed, either:\n" +
-		"  - revert storage_url (or the s3.* endpoint, bucket and prefix) in your\n" +
-		"    config to the bound destination, or\n" +
+		"  - revert storage_url in your config to the bound destination, or\n" +
 		"  - run 'vaultik database delete' to discard the local index and rebuild it\n" +
 		"    from a fresh full backup against the new destination"
 }

internal/vaultik/storage_bind_test.go

@@ -76,51 +76,3 @@ func TestEnsureStorageBinding_MismatchRefuses(t *testing.T) {
 	assert.Contains(t, err.Error(), "file:///mnt/backups/new")
 	assert.Contains(t, err.Error(), "vaultik database delete")
 }
-
-// A config with no storage_url names its destination with s3.endpoint,
-// s3.bucket and s3.prefix; a change to any of them must be refused just
-// as a changed storage_url is.
-func TestEnsureStorageBinding_S3FieldsChangeRefuses(t *testing.T) {
-	log.Initialize(log.Config{})
-	t.Parallel()
-
-	bound := config.S3Config{
-		Endpoint: "https://s3.example.com",
-		Bucket:   "bucket-a",
-		Prefix:   "backups",
-	}
-
-	tests := []struct {
-		name    string
-		changed config.S3Config
-	}{
-		{"bucket", config.S3Config{
-			Endpoint: bound.Endpoint, Bucket: "bucket-b", Prefix: bound.Prefix,
-		}},
-		{"prefix", config.S3Config{
-			Endpoint: bound.Endpoint, Bucket: bound.Bucket, Prefix: "other",
-		}},
-		{"endpoint", config.S3Config{
-			Endpoint: "https://s3.other.com", Bucket: bound.Bucket, Prefix: bound.Prefix,
-		}},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			t.Parallel()
-
-			tv, _ := buildBindTestVaultik(t, "")
-
-			tv.Config.S3 = bound
-			require.NoError(t, tv.EnsureStorageBinding(), "first use binds")
-			require.NoError(t, tv.EnsureStorageBinding(), "same destination passes")
-
-			tv.Config.S3 = tt.changed
-			err := tv.EnsureStorageBinding()
-			require.Error(t, err)
-			assert.Contains(t, err.Error(),
-				"local index is bound to a different backup destination")
-			assert.Contains(t, err.Error(), "vaultik database delete")
-		})
-	}
-}