From 135a5e1e3b1c8cf39ca55666886d9c97cce263ab Mon Sep 17 00:00:00 2001 From: CPerezz Date: Wed, 8 Apr 2026 00:42:37 +0200 Subject: [PATCH] triedb/pathdb: add regression test for zero-base-root lookup fallback MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit TestLookupZeroBaseRootFallback constructs a layer tree whose disk-layer root is common.Hash{} (mirroring the bintrie/verkle configuration where an empty trie hashes to EmptyVerkleHash), stacks diff layers on top, and exercises four cases: 1. lookupAccount on a never-written key must fall through to the disk layer and return (diskLayer, nil). Before the previous commit this returned errSnapshotStale because the disk-layer fallback hash collided with the stale sentinel. 2. Symmetric case for lookupStorage. 3. lookupAccount on a written account must still return the diff layer that holds it — pins the normal resolution path. 4. lookupAccount/lookupStorage for an unknown state root must still return errSnapshotStale. This pins the other half of the contract so a future refactor that always returned ok=true would be caught here rather than in production. Verified by reverse-applying the previous commit: the test fails with the exact pre-fix error ("layer stale") on cases 1 and 2, and passes once the fix is restored. The existing TestAccountLookup/TestStorageLookup tests use newTestLayerTree which hard-codes common.Hash{0x1} as the disk-layer root, so none of them could cover the zero-root case without a tailored helper; this test inlines newDiskLayer(common.Hash{}, …) directly rather than parameterize the shared helper. --- triedb/pathdb/layertree_test.go | 115 ++++++++++++++++++++++++++++++++ 1 file changed, 115 insertions(+) diff --git a/triedb/pathdb/layertree_test.go b/triedb/pathdb/layertree_test.go index 285ca67b6c..82eb182990 100644 --- a/triedb/pathdb/layertree_test.go +++ b/triedb/pathdb/layertree_test.go @@ -916,3 +916,118 @@ func TestStorageLookup(t *testing.T) { } } } + +// TestLookupZeroBaseRootFallback is a regression test for a sentinel +// collision in accountTip/storageTip: before the fix they returned +// common.Hash{} as both the "stale" marker and the disk-layer fallback +// when the disk root itself happened to be zero. lookupAccount/Storage +// then misreported a legitimate fallback as errSnapshotStale. +// +// On the merkle path the collision was invisible because the empty +// merkle trie hashes to types.EmptyRootHash (a concrete non-zero +// keccak), so the disk layer's root was never the zero hash in +// practice. The bug only surfaces once the disk layer root can +// legitimately be zero (for example a fresh verkle/bintrie database +// where the empty binary trie hashes to EmptyVerkleHash == +// common.Hash{}). +// +// The test constructs a layer tree whose base layer's root IS the zero +// hash, stacks diff layers on top, and exercises four cases: +// +// 1. Look up an account NEVER written → should fall through to the +// disk layer and return (diskLayer, nil). Before the fix this +// returned errSnapshotStale because the fallback hash collided +// with the sentinel. +// 2. Symmetric case for lookupStorage. +// 3. Look up an account written in a diff layer → should return that +// diff layer (the normal happy path is unaffected by the fix). +// 4. Look up any key at a state root that isn't part of the tree +// (neither the disk root nor a descendant of it) → MUST still +// return errSnapshotStale. This pins the "other half" of the +// contract so a future refactor that always returns ok=true would +// fail here. +func TestLookupZeroBaseRootFallback(t *testing.T) { + // Build a layer tree whose disk-layer root is common.Hash{} — + // mirrors the bintrie/verkle configuration where the empty trie + // hashes to EmptyVerkleHash. newTestLayerTree can't be reused + // because it hard-codes common.Hash{0x1}. + db := New(rawdb.NewMemoryDatabase(), nil, false) + base := newDiskLayer(common.Hash{}, 0, db, nil, nil, newBuffer(0, nil, nil, 0), nil) + tr := newLayerTree(base) + + // Stack two diff layers on the zero-rooted disk layer, each + // touching a known account and slot so we have something for the + // happy-path lookups to find later. + if err := tr.add( + common.Hash{0x2}, common.Hash{}, + 1, + NewNodeSetWithOrigin(nil, nil), + NewStateSetWithOrigin( + randomAccountSet("0xa"), + randomStorageSet([]string{"0xa"}, [][]string{{"0x1"}}, nil), + nil, nil, false), + ); err != nil { + t.Fatalf("add first diff layer: %v", err) + } + if err := tr.add( + common.Hash{0x3}, common.Hash{0x2}, + 2, + NewNodeSetWithOrigin(nil, nil), + NewStateSetWithOrigin( + randomAccountSet("0xb"), + nil, nil, nil, false), + ); err != nil { + t.Fatalf("add second diff layer: %v", err) + } + + // Case 1: unknown account queried at the head. The lookup must + // fall through the diff layers, hit the disk-layer fallback at + // base=common.Hash{}, and return the disk layer with no error — + // NOT errSnapshotStale. + l, err := tr.lookupAccount(common.HexToHash("0xdead"), common.Hash{0x3}) + if err != nil { + t.Fatalf("lookupAccount on zero-base disk layer: unexpected error %v", err) + } + if l.rootHash() != (common.Hash{}) { + t.Errorf("expected fall-through to disk layer (root=0), got %x", l.rootHash()) + } + + // Case 2: symmetric check for storage. Slot 0x99 was never written, + // so the lookup must fall through to the disk layer just like + // Case 1. + l, err = tr.lookupStorage( + common.HexToHash("0xdead"), common.HexToHash("0x99"), common.Hash{0x3}) + if err != nil { + t.Fatalf("lookupStorage on zero-base disk layer: unexpected error %v", err) + } + if l.rootHash() != (common.Hash{}) { + t.Errorf("expected fall-through to disk layer (root=0), got %x", l.rootHash()) + } + + // Case 3: happy path. Account 0xa was written at diff layer 0x2. + // The lookup must return that layer, proving the fix didn't break + // the normal resolution path. + l, err = tr.lookupAccount(common.HexToHash("0xa"), common.Hash{0x3}) + if err != nil { + t.Fatalf("lookupAccount(known): %v", err) + } + if l.rootHash() != (common.Hash{0x2}) { + t.Errorf("known account tip: want %x, got %x", + common.Hash{0x2}, l.rootHash()) + } + + // Case 4: truly stale state root. This pins the other half of the + // contract — the boolean must actually signal not-found for an + // unknown state, otherwise a refactor that always returned + // ok=true would still pass cases 1–3. + _, err = tr.lookupAccount(common.HexToHash("0xa"), common.HexToHash("0xdeadbeef")) + if !errors.Is(err, errSnapshotStale) { + t.Errorf("lookupAccount(stale state): want errSnapshotStale, got %v", err) + } + _, err = tr.lookupStorage( + common.HexToHash("0xa"), common.HexToHash("0x1"), + common.HexToHash("0xdeadbeef")) + if !errors.Is(err, errSnapshotStale) { + t.Errorf("lookupStorage(stale state): want errSnapshotStale, got %v", err) + } +}