133 lines
5.0 KiB
C++
133 lines
5.0 KiB
C++
/*
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* This file is part of the Flowee project
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* Copyright (C) 2009-2010 Satoshi Nakamoto
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* Copyright (C) 2009-2015 The Bitcoin Core developers
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* Copyright (C) 2020 Tom Zander <tom@flowee.org>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef FLOWEE_PARTIALMERKLETREE_H
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#define FLOWEE_PARTIALMERKLETREE_H
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#include "streaming/P2PParser.h"
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#include "serialize.h"
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#include "uint256.h"
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#include <vector>
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/** Data structure that represents a partial merkle tree.
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*
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* It represents a subset of the txid's of a known block, in a way that
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* allows recovery of the list of txid's and the merkle root, in an
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* authenticated way.
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*
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* The encoding works as follows: we traverse the tree in depth-first order,
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* storing a bit for each traversed node, signifying whether the node is the
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* parent of at least one matched leaf txid (or a matched txid itself). In
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* case we are at the leaf level, or this bit is 0, its merkle node hash is
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* stored, and its children are not explorer further. Otherwise, no hash is
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* stored, but we recurse into both (or the only) child branch. During
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* decoding, the same depth-first traversal is performed, consuming bits and
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* hashes as they written during encoding.
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*
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* The serialization is fixed and provides a hard guarantee about the
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* encoded size:
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*
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* SIZE <= 10 + ceil(32.25*N)
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*
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* Where N represents the number of leaf nodes of the partial tree. N itself
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* is bounded by:
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*
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* N <= total_transactions
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* N <= 1 + matched_transactions*tree_height
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*
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* The serialization format:
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* - uint32 total_transactions (4 bytes)
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* - varint number of hashes (1-3 bytes)
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* - uint256[] hashes in depth-first order (<= 32*N bytes)
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* - varint number of bytes of flag bits (1-3 bytes)
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* - byte[] flag bits, packed per 8 in a byte, least significant bit first (<= 2*N-1 bits)
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* The size constraints follow from this.
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*/
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class CPartialMerkleTree
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{
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protected:
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/** the total number of transactions in the block */
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unsigned int nTransactions;
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/** node-is-parent-of-matched-txid bits */
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std::vector<bool> vBits;
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/** txids and internal hashes */
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std::vector<uint256> vHash;
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/** flag set when encountering invalid data */
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bool fBad;
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/** helper function to efficiently calculate the number of nodes at given height in the merkle tree */
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unsigned int CalcTreeWidth(int height);
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/** calculate the hash of a node in the merkle tree (at leaf level: the txid's themselves) */
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uint256 CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid);
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/** recursive function that traverses tree nodes, storing the data as bits and hashes */
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void TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
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/**
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* recursive function that traverses tree nodes, consuming the bits and hashes produced by TraverseAndBuild.
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* it returns the hash of the respective node.
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*/
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uint256 TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<uint256> &vMatch);
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public:
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/** serialization implementation */
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ADD_SERIALIZE_METHODS
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template <typename Stream, typename Operation>
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inline void SerializationOp(Stream& s, Operation ser_action, int nType, int nVersion) {
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READWRITE(nTransactions);
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READWRITE(vHash);
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std::vector<unsigned char> vBytes;
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if (ser_action.ForRead()) {
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READWRITE(vBytes);
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CPartialMerkleTree &us = *(const_cast<CPartialMerkleTree*>(this));
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us.vBits.resize(vBytes.size() * 8);
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for (unsigned int p = 0; p < us.vBits.size(); p++)
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us.vBits[p] = (vBytes[p / 8] & (1 << (p % 8))) != 0;
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us.fBad = false;
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} else {
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vBytes.resize((vBits.size()+7)/8);
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for (unsigned int p = 0; p < vBits.size(); p++)
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vBytes[p / 8] |= vBits[p] << (p % 8);
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READWRITE(vBytes);
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}
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}
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static CPartialMerkleTree construct(Streaming::P2PParser &parser);
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/** Construct a partial merkle tree from a list of transaction ids, and a mask that selects a subset of them */
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CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
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CPartialMerkleTree();
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/**
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* extract the matching txid's represented by this partial merkle tree.
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* returns the merkle root, or 0 in case of failure
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*/
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uint256 ExtractMatches(std::vector<uint256> &vMatch);
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};
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#endif
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