dao: move header hash store logic out of the core

Which allows for more efficient buffer use along the way.

pkg/core/blockchain.go

@@ -949,15 +949,12 @@ func (bc *Blockchain) addHeaders(verify bool, headers ...*block.Header) error {
 	}
 
 	if oldlen != len(bc.headerHashes) {
-		buf := io.NewBufBinWriter()
 		for int(lastHeader.Index)-headerBatchCount >= int(bc.storedHeaderCount) {
-			buf.WriteArray(bc.headerHashes[bc.storedHeaderCount : bc.storedHeaderCount+headerBatchCount])
-			if buf.Err != nil {
-				return buf.Err
+			err = batch.StoreHeaderHashes(bc.headerHashes[bc.storedHeaderCount:bc.storedHeaderCount+headerBatchCount],
+				bc.storedHeaderCount)
+			if err != nil {
+				return err
 			}
-
-			key := storage.AppendPrefixInt(storage.IXHeaderHashList, int(bc.storedHeaderCount))
-			batch.Store.Put(key, buf.Bytes())
 			bc.storedHeaderCount += headerBatchCount
 		}
 

pkg/core/dao/dao.go

@@ -590,6 +590,25 @@ func read2000Uint256Hashes(b []byte) ([]util.Uint256, error) {
 	return hashes, nil
 }
 
+func (dao *Simple) mkHeaderHashKey(h uint32) []byte {
+	b := dao.getKeyBuf(1 + 4)
+	b[0] = byte(storage.IXHeaderHashList)
+	binary.BigEndian.PutUint32(b[1:], h)
+	return b
+}
+
+// StoreHeaderHashes pushes a batch of header hashes into the store.
+func (dao *Simple) StoreHeaderHashes(hashes []util.Uint256, height uint32) error {
+	key := dao.mkHeaderHashKey(height)
+	buf := dao.getDataBuf()
+	buf.WriteArray(hashes)
+	if buf.Err != nil {
+		return buf.Err
+	}
+	dao.Store.Put(key, buf.Bytes())
+	return nil
+}
+
 // HasTransaction returns nil if the given store does not contain the given
 // Transaction hash. It returns an error in case if transaction is in chain
 // or in the list of conflicting transactions.