core: split (*MemCachedStore) Seek and SeekAsync methods

Use SeekAsync for System.Storage.Find and Seek for the rest of cases.

pkg/core/dao/dao.go

@@ -338,10 +338,13 @@ func (dao *Simple) GetStorageItemsWithPrefix(id int32, prefix []byte) ([]state.S
 // Seek executes f for all items with a given prefix.
 // If key is to be used outside of f, they may not be copied.
 func (dao *Simple) Seek(id int32, prefix []byte, f func(k, v []byte)) {
-	res := dao.SeekAsync(context.Background(), id, prefix)
-	for r := range res {
-		f(r.Key, r.Value)
+	lookupKey := makeStorageItemKey(id, nil)
+	if prefix != nil {
+		lookupKey = append(lookupKey, prefix...)
 	}
+	dao.Store.Seek(lookupKey, func(k, v []byte) {
+		f(k[len(lookupKey):], v)
+	})
 }
 
 // SeekAsync sends all storage items matching given prefix to a channel and returns

pkg/core/storage/memcached_store.go

@@ -91,16 +91,28 @@ func (s *MemCachedStore) GetBatch() *MemBatch {
 
 // Seek implements the Store interface.
 func (s *MemCachedStore) Seek(key []byte, f func(k, v []byte)) {
-	seekres := s.SeekAsync(context.Background(), key, false)
-	for kv := range seekres {
-		f(kv.Key, kv.Value)
-	}
+	s.seek(context.Background(), key, false, f)
 }
 
 // SeekAsync returns non-buffered channel with matching KeyValue pairs. Key and
 // value slices may not be copied and may be modified. SeekAsync can guarantee
 // that key-value items are sorted by key in ascending way.
 func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bool) chan KeyValue {
+	res := make(chan KeyValue)
+	go func() {
+		s.seek(ctx, key, cutPrefix, func(k, v []byte) {
+			res <- KeyValue{
+				Key:   k,
+				Value: v,
+			}
+		})
+		close(res)
+	}()
+
+	return res
+}
+
+func (s *MemCachedStore) seek(ctx context.Context, key []byte, cutPrefix bool, f func(k, v []byte)) {
 	// Create memory store `mem` and `del` snapshot not to hold the lock.
 	var memRes []KeyValueExists
 	sk := string(key)
@@ -132,10 +144,6 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 		return bytes.Compare(memRes[i].Key, memRes[j].Key) < 0
 	})
 
-	var seekres = make(chan KeyValue)
-
-	// Seek over persistent store.
-	go func() {
 	var (
 		done    bool
 		iMem    int
@@ -147,7 +155,6 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 		haveMem = true
 		iMem++
 	}
-
 	// Merge results of seek operations in ascending order.
 	ps.Seek(key, func(k, v []byte) {
 		if done {
@@ -170,10 +177,7 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 						if cutPrefix {
 							kvMem.Key = kvMem.Key[len(key):]
 						}
-							seekres <- KeyValue{
-								Key:   kvMem.Key,
-								Value: kvMem.Value,
-							}
+						f(kvMem.Key, kvMem.Value)
 					}
 					if iMem < len(memRes) {
 						kvMem = memRes[iMem]
@@ -187,13 +191,12 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 						if cutPrefix {
 							kvPs.Key = kvPs.Key[len(key):]
 						}
-							seekres <- kvPs
+						f(kvPs.Key, kvPs.Value)
 					}
 					break loop
 				}
 			}
 		}
-
 	})
 	if !done && haveMem {
 	loop:
@@ -207,18 +210,11 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 					if cutPrefix {
 						kvMem.Key = kvMem.Key[len(key):]
 					}
-						seekres <- KeyValue{
-							Key:   kvMem.Key,
-							Value: kvMem.Value,
+					f(kvMem.Key, kvMem.Value)
 				}
 			}
 		}
 	}
-		}
-		close(seekres)
-	}()
-
-	return seekres
 }
 
 // Persist flushes all the MemoryStore contents into the (supposedly) persistent