You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: sync.go
    path of file: ./repos/go-ethereum/core/state
    
    the code of the file until where you have to start completion: // Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
//
    
func NewStateSync(root common.Hash, database ethdb.KeyValueReader, onLeaf func(keys [][]byte, leaf []byte) error, scheme string) *trie.Sync {
	// Register the storage slot callback if the external callback is specified.
	var onSlot func(keys [][]byte, path []byte, leaf []byte, parent common.Hash, parentPath []byte) error
	if onLeaf != nil {
		onSlot = func(keys [][]byte, path []byte, leaf []byte, parent common.Hash, parentPath []byte) error {
			return onLeaf(keys, leaf)
		}
	}
	// Register the account callback to connect the state trie and the storage
	// trie belongs to the contract.
	var syncer *trie.Sync
	onAccount := func(keys [][]byte, path []byte, leaf []byte, parent common.Hash, parentPath []byte) error {
		if onLeaf != nil {
			if err := onLeaf(keys, leaf); err != nil {
				return err
			}
		}
		var obj types.StateAccount
		if err := rlp.DecodeBytes(leaf, &obj); err != nil {
			return err
		}
		syncer.AddSubTrie(obj.Root, path, parent, parentPath, onSlot)
		syncer.AddCodeEntry(common.BytesToHash(obj.CodeHash), path, parent, parentPath)
		return nil
	}
	syncer = trie.NewSync(root, database, onAccount, scheme)
	return syncer
}