Line data    Source code

       1             : // Copyright (c) 2016-2022 The Bitcoin Core developers
       2             : // Distributed under the MIT software license, see the accompanying
       3             : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4             : 
       5             : #include <blockencodings.h>
       6             : #include <chainparams.h>
       7             : #include <common/system.h>
       8             : #include <consensus/consensus.h>
       9             : #include <consensus/validation.h>
      10             : #include <crypto/sha256.h>
      11             : #include <crypto/siphash.h>
      12             : #include <logging.h>
      13             : #include <random.h>
      14             : #include <streams.h>
      15             : #include <txmempool.h>
      16             : #include <validation.h>
      17           2 : 
      18           2 : #include <unordered_map>
      19             : 
      20           0 : CBlockHeaderAndShortTxIDs::CBlockHeaderAndShortTxIDs(const CBlock& block) :
      21           0 :         nonce(GetRand<uint64_t>()),
      22           0 :         shorttxids(block.vtx.size() - 1), prefilledtxn(1), header(block) {
      23           0 :     FillShortTxIDSelector();
      24             :     //TODO: Use our mempool prior to block acceptance to predictively fill more than just the coinbase
      25           0 :     prefilledtxn[0] = {0, block.vtx[0]};
      26           0 :     for (size_t i = 1; i < block.vtx.size(); i++) {
      27           0 :         const CTransaction& tx = *block.vtx[i];
      28           0 :         shorttxids[i - 1] = GetShortID(tx.GetWitnessHash());
      29           0 :     }
      30           0 : }
      31             : 
      32           0 : void CBlockHeaderAndShortTxIDs::FillShortTxIDSelector() const {
      33           0 :     DataStream stream{};
      34           0 :     stream << header << nonce;
      35           0 :     CSHA256 hasher;
      36           0 :     hasher.Write((unsigned char*)&(*stream.begin()), stream.end() - stream.begin());
      37           0 :     uint256 shorttxidhash;
      38           0 :     hasher.Finalize(shorttxidhash.begin());
      39           0 :     shorttxidk0 = shorttxidhash.GetUint64(0);
      40           0 :     shorttxidk1 = shorttxidhash.GetUint64(1);
      41           0 : }
      42             : 
      43           0 : uint64_t CBlockHeaderAndShortTxIDs::GetShortID(const uint256& txhash) const {
      44             :     static_assert(SHORTTXIDS_LENGTH == 6, "shorttxids calculation assumes 6-byte shorttxids");
      45           0 :     return SipHashUint256(shorttxidk0, shorttxidk1, txhash) & 0xffffffffffffL;
      46             : }
      47             : 
      48             : 
      49             : 
      50           0 : ReadStatus PartiallyDownloadedBlock::InitData(const CBlockHeaderAndShortTxIDs& cmpctblock, const std::vector<std::pair<uint256, CTransactionRef>>& extra_txn) {
      51           0 :     if (cmpctblock.header.IsNull() || (cmpctblock.shorttxids.empty() && cmpctblock.prefilledtxn.empty()))
      52           0 :         return READ_STATUS_INVALID;
      53           0 :     if (cmpctblock.shorttxids.size() + cmpctblock.prefilledtxn.size() > MAX_BLOCK_WEIGHT / MIN_SERIALIZABLE_TRANSACTION_WEIGHT)
      54           0 :         return READ_STATUS_INVALID;
      55             : 
      56           0 :     if (!header.IsNull() || !txn_available.empty()) return READ_STATUS_INVALID;
      57             : 
      58           0 :     header = cmpctblock.header;
      59           0 :     txn_available.resize(cmpctblock.BlockTxCount());
      60             : 
      61           0 :     int32_t lastprefilledindex = -1;
      62           0 :     for (size_t i = 0; i < cmpctblock.prefilledtxn.size(); i++) {
      63           0 :         if (cmpctblock.prefilledtxn[i].tx->IsNull())
      64           0 :             return READ_STATUS_INVALID;
      65             : 
      66           0 :         lastprefilledindex += cmpctblock.prefilledtxn[i].index + 1; //index is a uint16_t, so can't overflow here
      67           0 :         if (lastprefilledindex > std::numeric_limits<uint16_t>::max())
      68           0 :             return READ_STATUS_INVALID;
      69           0 :         if ((uint32_t)lastprefilledindex > cmpctblock.shorttxids.size() + i) {
      70             :             // If we are inserting a tx at an index greater than our full list of shorttxids
      71             :             // plus the number of prefilled txn we've inserted, then we have txn for which we
      72             :             // have neither a prefilled txn or a shorttxid!
      73           0 :             return READ_STATUS_INVALID;
      74           2 :         }
      75           0 :         txn_available[lastprefilledindex] = cmpctblock.prefilledtxn[i].tx;
      76           0 :     }
      77           0 :     prefilled_count = cmpctblock.prefilledtxn.size();
      78             : 
      79             :     // Calculate map of txids -> positions and check mempool to see what we have (or don't)
      80             :     // Because well-formed cmpctblock messages will have a (relatively) uniform distribution
      81             :     // of short IDs, any highly-uneven distribution of elements can be safely treated as a
      82             :     // READ_STATUS_FAILED.
      83           0 :     std::unordered_map<uint64_t, uint16_t> shorttxids(cmpctblock.shorttxids.size());
      84           0 :     uint16_t index_offset = 0;
      85           0 :     for (size_t i = 0; i < cmpctblock.shorttxids.size(); i++) {
      86           0 :         while (txn_available[i + index_offset])
      87           0 :             index_offset++;
      88           0 :         shorttxids[cmpctblock.shorttxids[i]] = i + index_offset;
      89             :         // To determine the chance that the number of entries in a bucket exceeds N,
      90             :         // we use the fact that the number of elements in a single bucket is
      91             :         // binomially distributed (with n = the number of shorttxids S, and p =
      92             :         // 1 / the number of buckets), that in the worst case the number of buckets is
      93             :         // equal to S (due to std::unordered_map having a default load factor of 1.0),
      94             :         // and that the chance for any bucket to exceed N elements is at most
      95             :         // buckets * (the chance that any given bucket is above N elements).
      96             :         // Thus: P(max_elements_per_bucket > N) <= S * (1 - cdf(binomial(n=S,p=1/S), N)).
      97             :         // If we assume blocks of up to 16000, allowing 12 elements per bucket should
      98             :         // only fail once per ~1 million block transfers (per peer and connection).
      99           0 :         if (shorttxids.bucket_size(shorttxids.bucket(cmpctblock.shorttxids[i])) > 12)
     100           0 :             return READ_STATUS_FAILED;
     101           0 :     }
     102             :     // TODO: in the shortid-collision case, we should instead request both transactions
     103             :     // which collided. Falling back to full-block-request here is overkill.
     104           0 :     if (shorttxids.size() != cmpctblock.shorttxids.size())
     105           0 :         return READ_STATUS_FAILED; // Short ID collision
     106             : 
     107           0 :     std::vector<bool> have_txn(txn_available.size());
     108             :     {
     109           0 :     LOCK(pool->cs);
     110           0 :     for (size_t i = 0; i < pool->vTxHashes.size(); i++) {
     111           0 :         uint64_t shortid = cmpctblock.GetShortID(pool->vTxHashes[i].first);
     112           0 :         std::unordered_map<uint64_t, uint16_t>::iterator idit = shorttxids.find(shortid);
     113           0 :         if (idit != shorttxids.end()) {
     114           0 :             if (!have_txn[idit->second]) {
     115           0 :                 txn_available[idit->second] = pool->vTxHashes[i].second->GetSharedTx();
     116           0 :                 have_txn[idit->second]  = true;
     117           0 :                 mempool_count++;
     118           0 :             } else {
     119             :                 // If we find two mempool txn that match the short id, just request it.
     120             :                 // This should be rare enough that the extra bandwidth doesn't matter,
     121             :                 // but eating a round-trip due to FillBlock failure would be annoying
     122           0 :                 if (txn_available[idit->second]) {
     123           0 :                     txn_available[idit->second].reset();
     124           0 :                     mempool_count--;
     125           0 :                 }
     126             :             }
     127           0 :         }
     128             :         // Though ideally we'd continue scanning for the two-txn-match-shortid case,
     129             :         // the performance win of an early exit here is too good to pass up and worth
     130             :         // the extra risk.
     131           0 :         if (mempool_count == shorttxids.size())
     132           0 :             break;
     133           0 :     }
     134           0 :     }
     135             : 
     136           0 :     for (size_t i = 0; i < extra_txn.size(); i++) {
     137           0 :         uint64_t shortid = cmpctblock.GetShortID(extra_txn[i].first);
     138           0 :         std::unordered_map<uint64_t, uint16_t>::iterator idit = shorttxids.find(shortid);
     139           0 :         if (idit != shorttxids.end()) {
     140           0 :             if (!have_txn[idit->second]) {
     141           0 :                 txn_available[idit->second] = extra_txn[i].second;
     142           0 :                 have_txn[idit->second]  = true;
     143           0 :                 mempool_count++;
     144           0 :                 extra_count++;
     145           0 :             } else {
     146             :                 // If we find two mempool/extra txn that match the short id, just
     147             :                 // request it.
     148             :                 // This should be rare enough that the extra bandwidth doesn't matter,
     149             :                 // but eating a round-trip due to FillBlock failure would be annoying
     150             :                 // Note that we don't want duplication between extra_txn and mempool to
     151             :                 // trigger this case, so we compare witness hashes first
     152           0 :                 if (txn_available[idit->second] &&
     153           0 :                         txn_available[idit->second]->GetWitnessHash() != extra_txn[i].second->GetWitnessHash()) {
     154           0 :                     txn_available[idit->second].reset();
     155           0 :                     mempool_count--;
     156           0 :                     extra_count--;
     157           0 :                 }
     158             :             }
     159           0 :         }
     160             :         // Though ideally we'd continue scanning for the two-txn-match-shortid case,
     161             :         // the performance win of an early exit here is too good to pass up and worth
     162             :         // the extra risk.
     163           0 :         if (mempool_count == shorttxids.size())
     164           0 :             break;
     165           0 :     }
     166             : 
     167           0 :     LogPrint(BCLog::CMPCTBLOCK, "Initialized PartiallyDownloadedBlock for block %s using a cmpctblock of size %lu\n", cmpctblock.header.GetHash().ToString(), GetSerializeSize(cmpctblock, PROTOCOL_VERSION));
     168             : 
     169           0 :     return READ_STATUS_OK;
     170           0 : }
     171             : 
     172           0 : bool PartiallyDownloadedBlock::IsTxAvailable(size_t index) const
     173             : {
     174           0 :     if (header.IsNull()) return false;
     175             : 
     176           0 :     assert(index < txn_available.size());
     177           0 :     return txn_available[index] != nullptr;
     178           0 : }
     179             : 
     180           0 : ReadStatus PartiallyDownloadedBlock::FillBlock(CBlock& block, const std::vector<CTransactionRef>& vtx_missing)
     181             : {
     182           0 :     if (header.IsNull()) return READ_STATUS_INVALID;
     183             : 
     184           0 :     uint256 hash = header.GetHash();
     185           0 :     block = header;
     186           0 :     block.vtx.resize(txn_available.size());
     187             : 
     188           0 :     size_t tx_missing_offset = 0;
     189           0 :     for (size_t i = 0; i < txn_available.size(); i++) {
     190           0 :         if (!txn_available[i]) {
     191           0 :             if (vtx_missing.size() <= tx_missing_offset)
     192           0 :                 return READ_STATUS_INVALID;
     193           0 :             block.vtx[i] = vtx_missing[tx_missing_offset++];
     194           0 :         } else
     195           0 :             block.vtx[i] = std::move(txn_available[i]);
     196           0 :     }
     197             : 
     198             :     // Make sure we can't call FillBlock again.
     199           0 :     header.SetNull();
     200           0 :     txn_available.clear();
     201             : 
     202           0 :     if (vtx_missing.size() != tx_missing_offset)
     203           0 :         return READ_STATUS_INVALID;
     204             : 
     205           0 :     BlockValidationState state;
     206           0 :     CheckBlockFn check_block = m_check_block_mock ? m_check_block_mock : CheckBlock;
     207           0 :     if (!check_block(block, state, Params().GetConsensus(), /*fCheckPoW=*/true, /*fCheckMerkleRoot=*/true)) {
     208             :         // TODO: We really want to just check merkle tree manually here,
     209             :         // but that is expensive, and CheckBlock caches a block's
     210             :         // "checked-status" (in the CBlock?). CBlock should be able to
     211             :         // check its own merkle root and cache that check.
     212           0 :         if (state.GetResult() == BlockValidationResult::BLOCK_MUTATED)
     213           0 :             return READ_STATUS_FAILED; // Possible Short ID collision
     214           0 :         return READ_STATUS_CHECKBLOCK_FAILED;
     215             :     }
     216             : 
     217           0 :     LogPrint(BCLog::CMPCTBLOCK, "Successfully reconstructed block %s with %lu txn prefilled, %lu txn from mempool (incl at least %lu from extra pool) and %lu txn requested\n", hash.ToString(), prefilled_count, mempool_count, extra_count, vtx_missing.size());
     218           0 :     if (vtx_missing.size() < 5) {
     219           0 :         for (const auto& tx : vtx_missing) {
     220           0 :             LogPrint(BCLog::CMPCTBLOCK, "Reconstructed block %s required tx %s\n", hash.ToString(), tx->GetHash().ToString());
     221             :         }
     222           0 :     }
     223             : 
     224           0 :     return READ_STATUS_OK;
     225           0 : }