storage: generalize Level/Bolt seek implementations

Too much in common. Just refactoring. no functional changes.

pkg/core/storage/boltdb_store.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/util/slice"
-	"github.com/syndtr/goleveldb/leveldb/util"
 	"go.etcd.io/bbolt"
 )
 
@@ -110,44 +109,30 @@ func (s *BoltDBStore) PutChangeSet(puts map[string][]byte) error {
 
 // Seek implements the Store interface.
 func (s *BoltDBStore) Seek(rng SeekRange, f func(k, v []byte) bool) {
-	start := make([]byte, len(rng.Prefix)+len(rng.Start))
-	copy(start, rng.Prefix)
-	copy(start[len(rng.Prefix):], rng.Start)
-	if rng.Backwards {
-		s.seekBackwards(rng.Prefix, start, f)
+	rang := seekRangeToPrefixes(rng)
+	err := s.db.View(func(tx *bbolt.Tx) error {
+		var (
+			k, v []byte
+			next func() ([]byte, []byte)
+		)
+
+		c := tx.Bucket(Bucket).Cursor()
+
+		if !rng.Backwards {
+			k, v = c.Seek(rang.Start)
+			next = c.Next
 		} else {
-		s.seek(rng.Prefix, start, f)
-	}
-}
-
-func (s *BoltDBStore) seek(key []byte, start []byte, f func(k, v []byte) bool) {
-	prefix := util.BytesPrefix(key)
-	prefix.Start = start
-	err := s.db.View(func(tx *bbolt.Tx) error {
-		c := tx.Bucket(Bucket).Cursor()
-		for k, v := c.Seek(prefix.Start); k != nil && (len(prefix.Limit) == 0 || bytes.Compare(k, prefix.Limit) <= 0); k, v = c.Next() {
-			if !f(k, v) {
-				break
-			}
-		}
-		return nil
-	})
-	if err != nil {
-		panic(err)
-	}
-}
-
-func (s *BoltDBStore) seekBackwards(key []byte, start []byte, f func(k, v []byte) bool) {
-	err := s.db.View(func(tx *bbolt.Tx) error {
-		c := tx.Bucket(Bucket).Cursor()
-		// Move cursor to the first kv pair which is followed by the pair matching the specified prefix.
-		if len(start) == 0 {
+			if len(rang.Limit) == 0 {
 				lastKey, _ := c.Last()
-			start = lastKey
+				k, v = c.Seek(lastKey)
+			} else {
+				c.Seek(rang.Limit)
+				k, v = c.Prev()
 			}
-		rng := util.BytesPrefix(start) // in fact, we only need limit based on start slice to iterate backwards starting from this limit
-		c.Seek(rng.Limit)
-		for k, v := c.Prev(); k != nil && bytes.HasPrefix(k, key); k, v = c.Prev() {
+			next = c.Prev
+		}
+
+		for ; k != nil && bytes.HasPrefix(k, rng.Prefix) && (len(rang.Limit) == 0 || bytes.Compare(k, rang.Limit) <= 0); k, v = next() {
 			if !f(k, v) {
 				break
 			}

pkg/core/storage/leveldb_store.go

@@ -4,7 +4,6 @@ import (
 	"github.com/syndtr/goleveldb/leveldb"
 	"github.com/syndtr/goleveldb/leveldb/filter"
 	"github.com/syndtr/goleveldb/leveldb/opt"
-	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
 // LevelDBOptions configuration for LevelDB.
@@ -83,34 +82,21 @@ func (s *LevelDBStore) PutChangeSet(puts map[string][]byte) error {
 
 // Seek implements the Store interface.
 func (s *LevelDBStore) Seek(rng SeekRange, f func(k, v []byte) bool) {
-	start := make([]byte, len(rng.Prefix)+len(rng.Start))
-	copy(start, rng.Prefix)
-	copy(start[len(rng.Prefix):], rng.Start)
-	if rng.Backwards {
-		s.seekBackwards(rng.Prefix, start, f)
+	var (
+		next func() bool
+		ok   bool
+		iter = s.db.NewIterator(seekRangeToPrefixes(rng), nil)
+	)
+
+	if !rng.Backwards {
+		ok = iter.Next()
+		next = iter.Next
 	} else {
-		s.seek(rng.Prefix, start, f)
-	}
+		ok = iter.Last()
+		next = iter.Prev
 	}
 
-func (s *LevelDBStore) seek(key []byte, start []byte, f func(k, v []byte) bool) {
-	prefix := util.BytesPrefix(key)
-	prefix.Start = start
-	iter := s.db.NewIterator(prefix, nil)
-	for iter.Next() {
-		if !f(iter.Key(), iter.Value()) {
-			break
-		}
-	}
-	iter.Release()
-}
-
-func (s *LevelDBStore) seekBackwards(key []byte, start []byte, f func(k, v []byte) bool) {
-	iRange := util.BytesPrefix(start)
-	iRange.Start = key
-
-	iter := s.db.NewIterator(iRange, nil)
-	for ok := iter.Last(); ok; ok = iter.Prev() {
+	for ; ok; ok = next() {
 		if !f(iter.Key(), iter.Value()) {
 			break
 		}

pkg/core/storage/store.go

@@ -4,6 +4,8 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+
+	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
 // KeyPrefix constants.
@@ -133,6 +135,24 @@ func AppendPrefixInt(k KeyPrefix, n int) []byte {
 	return AppendPrefix(k, b)
 }
 
+func seekRangeToPrefixes(sr SeekRange) *util.Range {
+	var (
+		rang  *util.Range
+		start = make([]byte, len(sr.Prefix)+len(sr.Start))
+	)
+	copy(start, sr.Prefix)
+	copy(start[len(sr.Prefix):], sr.Start)
+
+	if !sr.Backwards {
+		rang = util.BytesPrefix(sr.Prefix)
+		rang.Start = start
+	} else {
+		rang = util.BytesPrefix(start)
+		rang.Start = sr.Prefix
+	}
+	return rang
+}
+
 // NewStore creates storage with preselected in configuration database type.
 func NewStore(cfg DBConfiguration) (Store, error) {
 	var store Store