chain: Fix MemDB Iter not observing unflushed writes

Author: lukechampine

chain/db.go

@@ -293,6 +293,14 @@ func (b memBucket) Iter() iter.Seq2[[]byte, []byte] {
 				return
 			}
 		}
+		for key, val := range b.db.puts[b.name] {
+			if _, ok := b.db.gen.buckets[b.name][key]; ok {
+				continue // already yielded above
+			}
+			if !yield([]byte(key), val) {
+				return
+			}
+		}
 	}
 }
 
@@ -572,7 +580,6 @@ func getState(ss DBSnapshot, n *consensus.Network, id types.BlockID) (consensus.
 	return vs.State, ok
 }
 
-// tipState returns the consensus state of the best chain.s tip.
 func tipState(ss DBSnapshot, n *consensus.Network) consensus.State {
 	index, _ := bestIndex(ss, getHeight(ss))
 	cs, _ := getState(ss, n, index.ID)

chain/db_test.go

@@ -373,6 +373,16 @@ func testDBSnapshot(t *testing.T, db chain.DB) {
 	} else if !bytes.Equal(b.Get([]byte("baz")), []byte("quux")) {
 		t.Fatal("expected unflushed write to be visible via the scratchpad")
 	}
+	var iterated int
+	for k, v := range b.Iter() {
+		if !bytes.Equal(k, []byte("baz")) || !bytes.Equal(v, []byte("quux")) {
+			t.Fatal("unexpected key-value pair:", string(k), string(v))
+		}
+		iterated++
+	}
+	if iterated != 1 {
+		t.Fatal("expected unflushed write to be visible via scratchpad iteration")
+	}
 	snapshot, release := db.Snapshot()
 	if vb := snapshot.Bucket([]byte("nonexistent")); vb != nil {
 		t.Fatal("expected nil bucket for nonexistent bucket")

chain/manager.go

@@ -53,7 +53,7 @@ type Store interface {
 	// prevent the Store from shutting down.
 	Snapshot() (ss StoreSnapshot, release func())
 	// Scratchpad returns a handle to the current scratchpad, which observes
-	// the Store.s uncommitted data.
+	// the Store's uncommitted data.
 	Scratchpad() StoreScratchpad
 }