merkledb -- use Maybe for start bounds

proto/sync/sync.proto

@@ -54,7 +54,7 @@ message Proof {
 message SyncGetChangeProofRequest {
   bytes start_root_hash = 1;
   bytes end_root_hash = 2;
-  bytes start_key = 3;
+  MaybeBytes start_key = 3;
   MaybeBytes end_key = 4;
   uint32 key_limit = 5;
   uint32 bytes_limit = 6;
@@ -70,7 +70,7 @@ message SyncGetChangeProofResponse {
 message GetChangeProofRequest {
   bytes start_root_hash = 1;
   bytes end_root_hash = 2;
-  bytes start_key = 3;
+  MaybeBytes start_key = 3;
   MaybeBytes end_key = 4;
   uint32 key_limit = 5;
 }
@@ -85,8 +85,8 @@ message GetChangeProofResponse {
 
 message VerifyChangeProofRequest {
   ChangeProof proof = 1;
-  bytes start_key = 2;
-  bytes end_key = 3;
+  MaybeBytes start_key = 2;
+  MaybeBytes end_key = 3;
   bytes expected_root_hash = 4;
 }
 
@@ -103,15 +103,15 @@ message CommitChangeProofRequest {
 // the response. GetRangeProof in the DB service doesn't.
 message SyncGetRangeProofRequest {
   bytes root_hash = 1;
-  bytes start_key = 2;
+  MaybeBytes start_key = 2;
   MaybeBytes end_key = 3;
   uint32 key_limit = 4;
   uint32 bytes_limit = 5;
 }
 
 message GetRangeProofRequest {
   bytes root_hash = 1;
-  bytes start_key = 2;
+  MaybeBytes start_key = 2;
   MaybeBytes end_key = 3;
   uint32 key_limit = 4;
 }
@@ -121,7 +121,7 @@ message GetRangeProofResponse {
 }
 
 message CommitRangeProofRequest {
-  bytes start_key = 1;
+  MaybeBytes start_key = 1;
   RangeProof range_proof = 2;
 }
 

utils/maybe/maybe.go

@@ -3,18 +3,23 @@
 
 package maybe
 
+import "fmt"
+
 // Maybe T = Some T | Nothing.
 // A data wrapper that allows values to be something [Some T] or nothing [Nothing].
+// Invariant: If [hasValue] is false, then [value] is the zero value of type T.
 // Maybe is used to wrap types:
 // * That can't be represented by nil.
 // * That use nil as a valid value instead of an indicator of a missing value.
 // For more info see https://en.wikipedia.org/wiki/Option_type
 type Maybe[T any] struct {
 	hasValue bool
-	value    T
+	// If [hasValue] is false, [value] is the zero value of type T.
+	value T
 }
 
 // Some returns a new Maybe[T] with the value val.
+// If m.IsNothing(), returns the zero value of type T.
 func Some[T any](val T) Maybe[T] {
 	return Maybe[T]{
 		value:    val,
@@ -42,6 +47,13 @@ func (m Maybe[T]) Value() T {
 	return m.value
 }
 
+func (m Maybe[T]) String() string {
+	if !m.hasValue {
+		return fmt.Sprintf("Nothing[%T]", m.value)
+	}
+	return fmt.Sprintf("Some[%T]{%v}", m.value, m.value)
+}
+
 // Bind returns Nothing iff [m] is Nothing.
 // Otherwise applies [f] to the value of [m] and returns the result as a Some.
 func Bind[T, U any](m Maybe[T], f func(T) U) Maybe[U] {

utils/maybe/maybe_test.go

@@ -32,6 +32,23 @@ func TestMaybeClone(t *testing.T) {
 	}
 }
 
+func TestMaybeString(t *testing.T) {
+	require := require.New(t)
+
+	// Case: Value is maybe
+	{
+		val := []int{1, 2, 3}
+		m := Some(val)
+		require.Equal("Some[[]int]{[1 2 3]}", m.String())
+	}
+
+	// Case: Value is nothing
+	{
+		m := Nothing[int]()
+		require.Equal("Nothing[int]", m.String())
+	}
+}
+
 func TestMaybeEquality(t *testing.T) {
 	require := require.New(t)
 	require.True(Equal(Nothing[int](), Nothing[int](), func(i int, i2 int) bool {

x/merkledb/db.go

@@ -63,7 +63,7 @@ type ChangeProofer interface {
 		ctx context.Context,
 		startRootID ids.ID,
 		endRootID ids.ID,
-		start []byte,
+		start maybe.Maybe[[]byte],
 		end maybe.Maybe[[]byte],
 		maxLength int,
 	) (*ChangeProof, error)
@@ -72,7 +72,7 @@ type ChangeProofer interface {
 	//   - [start] <= [end].
 	//   - [proof] is non-empty.
 	//   - All keys in [proof.KeyValues] and [proof.DeletedKeys] are in [start, end].
-	//     If [start] is empty, all keys are considered > [start].
+	//     If [start] is nothing, all keys are considered > [start].
 	//     If [end] is nothing, all keys are considered < [end].
 	//   - [proof.KeyValues] and [proof.DeletedKeys] are sorted in order of increasing key.
 	//   - [proof.StartProof] and [proof.EndProof] are well-formed.
@@ -84,7 +84,7 @@ type ChangeProofer interface {
 	VerifyChangeProof(
 		ctx context.Context,
 		proof *ChangeProof,
-		start []byte,
+		start maybe.Maybe[[]byte],
 		end maybe.Maybe[[]byte],
 		expectedEndRootID ids.ID,
 	) error
@@ -96,17 +96,19 @@ type ChangeProofer interface {
 type RangeProofer interface {
 	// GetRangeProofAtRoot returns a proof for the key/value pairs in this trie within the range
 	// [start, end] when the root of the trie was [rootID].
+	// If [start] is Nothing, there's no lower bound on the range.
+	// If [end] is Nothing, there's no upper bound on the range.
 	GetRangeProofAtRoot(
 		ctx context.Context,
 		rootID ids.ID,
-		start []byte,
+		start maybe.Maybe[[]byte],
 		end maybe.Maybe[[]byte],
 		maxLength int,
 	) (*RangeProof, error)
 
 	// CommitRangeProof commits the key/value pairs within the [proof] to the db.
 	// [start] is the smallest key in the range this [proof] covers.
-	CommitRangeProof(ctx context.Context, start []byte, proof *RangeProof) error
+	CommitRangeProof(ctx context.Context, start maybe.Maybe[[]byte], proof *RangeProof) error
 }
 
 type MerkleDB interface {
@@ -314,7 +316,7 @@ func (db *merkleDB) CommitChangeProof(ctx context.Context, proof *ChangeProof) e
 	return view.commitToDB(ctx)
 }
 
-func (db *merkleDB) CommitRangeProof(ctx context.Context, start []byte, proof *RangeProof) error {
+func (db *merkleDB) CommitRangeProof(ctx context.Context, start maybe.Maybe[[]byte], proof *RangeProof) error {
 	db.commitLock.Lock()
 	defer db.commitLock.Unlock()
 
@@ -336,7 +338,7 @@ func (db *merkleDB) CommitRangeProof(ctx context.Context, start []byte, proof *R
 	if len(proof.KeyValues) > 0 {
 		largestKey = proof.KeyValues[len(proof.KeyValues)-1].Key
 	}
-	keysToDelete, err := db.getKeysNotInSet(start, largestKey, keys)
+	keysToDelete, err := db.getKeysNotInSet(start.Value(), largestKey, keys)
 	if err != nil {
 		return err
 	}
@@ -509,11 +511,9 @@ func (db *merkleDB) getProof(ctx context.Context, key []byte) (*Proof, error) {
 	return view.getProof(ctx, key)
 }
 
-// GetRangeProof returns a proof for the key/value pairs in this trie within the range
-// [start, end].
 func (db *merkleDB) GetRangeProof(
 	ctx context.Context,
-	start []byte,
+	start maybe.Maybe[[]byte],
 	end maybe.Maybe[[]byte],
 	maxLength int,
 ) (*RangeProof, error) {
@@ -523,12 +523,10 @@ func (db *merkleDB) GetRangeProof(
 	return db.getRangeProofAtRoot(ctx, db.getMerkleRoot(), start, end, maxLength)
 }
 
-// GetRangeProofAtRoot returns a proof for the key/value pairs in this trie within the range
-// [start, end] when the root of the trie was [rootID].
 func (db *merkleDB) GetRangeProofAtRoot(
 	ctx context.Context,
 	rootID ids.ID,
-	start []byte,
+	start maybe.Maybe[[]byte],
 	end maybe.Maybe[[]byte],
 	maxLength int,
 ) (*RangeProof, error) {
@@ -542,7 +540,7 @@ func (db *merkleDB) GetRangeProofAtRoot(
 func (db *merkleDB) getRangeProofAtRoot(
 	ctx context.Context,
 	rootID ids.ID,
-	start []byte,
+	start maybe.Maybe[[]byte],
 	end maybe.Maybe[[]byte],
 	maxLength int,
 ) (*RangeProof, error) {
@@ -564,11 +562,11 @@ func (db *merkleDB) GetChangeProof(
 	ctx context.Context,
 	startRootID ids.ID,
 	endRootID ids.ID,
-	start []byte,
+	start maybe.Maybe[[]byte],
 	end maybe.Maybe[[]byte],
 	maxLength int,
 ) (*ChangeProof, error) {
-	if end.HasValue() && bytes.Compare(start, end.Value()) == 1 {
+	if start.HasValue() && end.HasValue() && bytes.Compare(start.Value(), end.Value()) == 1 {
 		return nil, ErrStartAfterEnd
 	}
 	if startRootID == endRootID {
@@ -628,8 +626,8 @@ func (db *merkleDB) GetChangeProof(
 		result.EndProof = endProof.Path
 	}
 
-	if len(start) > 0 {
-		startProof, err := historicalView.getProof(ctx, start)
+	if start.HasValue() {
+		startProof, err := historicalView.getProof(ctx, start.Value())
 		if err != nil {
 			return nil, err
 		}
@@ -988,19 +986,19 @@ func (*merkleDB) CommitToDB(context.Context) error {
 func (db *merkleDB) VerifyChangeProof(
 	ctx context.Context,
 	proof *ChangeProof,
-	start []byte,
+	start maybe.Maybe[[]byte],
 	end maybe.Maybe[[]byte],
 	expectedEndRootID ids.ID,
 ) error {
 	switch {
-	case end.HasValue() && bytes.Compare(start, end.Value()) > 0:
+	case start.HasValue() && end.HasValue() && bytes.Compare(start.Value(), end.Value()) > 0:
 		return ErrStartAfterEnd
 	case proof.Empty():
 		return ErrNoMerkleProof
 	case end.HasValue() && len(proof.KeyChanges) == 0 && len(proof.EndProof) == 0:
 		// We requested an end proof but didn't get one.
 		return ErrNoEndProof
-	case len(start) > 0 && len(proof.StartProof) == 0 && len(proof.EndProof) == 0:
+	case start.HasValue() && len(proof.StartProof) == 0 && len(proof.EndProof) == 0:
 		// We requested a start proof but didn't get one.
 		// Note that we also have to check that [proof.EndProof] is empty
 		// to handle the case that the start proof is empty because all
@@ -1013,7 +1011,8 @@ func (db *merkleDB) VerifyChangeProof(
 		return err
 	}
 
-	smallestPath := newPath(start)
+	// Note that if [start] is Nothing, smallestPath is the empty path.
+	smallestPath := newPath(start.Value())
 
 	// Make sure the start proof, if given, is well-formed.
 	if err := verifyProofPath(proof.StartProof, smallestPath); err != nil {
@@ -1179,10 +1178,12 @@ func (db *merkleDB) initializeRootIfNeeded() (ids.ID, error) {
 }
 
 // Returns a view of the trie as it was when it had root [rootID] for keys within range [start, end].
+// If [start] is Nothing, there's no lower bound on the range.
+// If [end] is Nothing, there's no upper bound on the range.
 // Assumes [db.commitLock] is read locked.
 func (db *merkleDB) getHistoricalViewForRange(
 	rootID ids.ID,
-	start []byte,
+	start maybe.Maybe[[]byte],
 	end maybe.Maybe[[]byte],
 ) (*trieView, error) {
 	currentRootID := db.getMerkleRoot()

x/merkledb/db_test.go

@@ -266,13 +266,13 @@ func Test_MerkleDB_Commit_Proof_To_Empty_Trie(t *testing.T) {
 	require.NoError(batch.Put([]byte("key3"), []byte("3")))
 	require.NoError(batch.Write())
 
-	proof, err := db.GetRangeProof(context.Background(), []byte("key1"), maybe.Some([]byte("key3")), 10)
+	proof, err := db.GetRangeProof(context.Background(), maybe.Some([]byte("key1")), maybe.Some([]byte("key3")), 10)
 	require.NoError(err)
 
 	freshDB, err := getBasicDB()
 	require.NoError(err)
 
-	require.NoError(freshDB.CommitRangeProof(context.Background(), []byte("key1"), proof))
+	require.NoError(freshDB.CommitRangeProof(context.Background(), maybe.Some([]byte("key1")), proof))
 
 	value, err := freshDB.Get([]byte("key2"))
 	require.NoError(err)
@@ -296,7 +296,7 @@ func Test_MerkleDB_Commit_Proof_To_Filled_Trie(t *testing.T) {
 	require.NoError(batch.Put([]byte("key3"), []byte("3")))
 	require.NoError(batch.Write())
 
-	proof, err := db.GetRangeProof(context.Background(), []byte("key1"), maybe.Some([]byte("key3")), 10)
+	proof, err := db.GetRangeProof(context.Background(), maybe.Some([]byte("key1")), maybe.Some([]byte("key3")), 10)
 	require.NoError(err)
 
 	freshDB, err := getBasicDB()
@@ -308,7 +308,7 @@ func Test_MerkleDB_Commit_Proof_To_Filled_Trie(t *testing.T) {
 	require.NoError(batch.Put([]byte("key25"), []byte("5")))
 	require.NoError(batch.Write())
 
-	require.NoError(freshDB.CommitRangeProof(context.Background(), []byte("key1"), proof))
+	require.NoError(freshDB.CommitRangeProof(context.Background(), maybe.Some([]byte("key1")), proof))
 
 	value, err := freshDB.Get([]byte("key2"))
 	require.NoError(err)
@@ -747,16 +747,20 @@ func runRandDBTest(require *require.Assertions, r *rand.Rand, rt randTest) {
 			if len(pastRoots) > 0 {
 				root = pastRoots[r.Intn(len(pastRoots))]
 			}
+			start := maybe.Nothing[[]byte]()
+			if len(step.key) > 0 {
+				start = maybe.Some(step.key)
+			}
 			end := maybe.Nothing[[]byte]()
 			if len(step.value) > 0 {
 				end = maybe.Some(step.value)
 			}
 
-			rangeProof, err := db.GetRangeProofAtRoot(context.Background(), root, step.key, end, 100)
+			rangeProof, err := db.GetRangeProofAtRoot(context.Background(), root, start, end, 100)
 			require.NoError(err)
 			require.NoError(rangeProof.Verify(
 				context.Background(),
-				step.key,
+				start,
 				end,
 				root,
 			))
@@ -771,8 +775,12 @@ func runRandDBTest(require *require.Assertions, r *rand.Rand, rt randTest) {
 			if len(step.value) > 0 {
 				end = maybe.Some(step.value)
 			}
+			start := maybe.Nothing[[]byte]()
+			if len(step.key) > 0 {
+				start = maybe.Some(step.key)
+			}
 
-			changeProof, err := db.GetChangeProof(context.Background(), startRoot, root, step.key, end, 100)
+			changeProof, err := db.GetChangeProof(context.Background(), startRoot, root, start, end, 100)
 			if startRoot == root {
 				require.ErrorIs(err, errSameRoot)
 				continue
@@ -784,7 +792,7 @@ func runRandDBTest(require *require.Assertions, r *rand.Rand, rt randTest) {
 			require.NoError(changeProofDB.VerifyChangeProof(
 				context.Background(),
 				changeProof,
-				step.key,
+				start,
 				end,
 				root,
 			))