Line data    Source code

       1             : // Copyright (c) 2016-2020 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 <consensus/consensus.h>
       7             : #include <consensus/validation.h>
       8             : #include <chainparams.h>
       9             : #include <crypto/sha256.h>
      10             : #include <crypto/siphash.h>
      11             : #include <random.h>
      12             : #include <streams.h>
      13             : #include <txmempool.h>
      14             : #include <validation.h>
      15             : #include <util/system.h>
      16             : 
      17             : #include <unordered_map>
      18             : 
      19             : #define MIN_TRANSACTION_SIZE (::GetSerializeSize(CMutableTransaction(), PROTOCOL_VERSION))
      20             : 
      21           8 : CBlockHeaderAndShortTxIDs::CBlockHeaderAndShortTxIDs(const CBlock& block) :
      22           4 :         nonce(GetRand<uint64_t>()),
      23           8 :         shorttxids(block.vtx.size() - 1), prefilledtxn(1), header(block) {
      24           4 :     FillShortTxIDSelector();
      25             :     //TODO: Use our mempool prior to block acceptance to predictively fill more than just the coinbase
      26           4 :     prefilledtxn[0] = {0, block.vtx[0]};
      27          10 :     for (size_t i = 1; i < block.vtx.size(); i++) {
      28           6 :         const CTransaction& tx = *block.vtx[i];
      29           6 :         shorttxids[i - 1] = GetShortID(tx.GetHash());
      30           6 :     }
      31           8 : }
      32             : 
      33          11 : void CBlockHeaderAndShortTxIDs::FillShortTxIDSelector() const {
      34          11 :     CDataStream stream(SER_NETWORK, PROTOCOL_VERSION);
      35          11 :     stream << header << nonce;
      36          11 :     CSHA256 hasher;
      37          11 :     hasher.Write((unsigned char*)&(*stream.begin()), stream.end() - stream.begin());
      38          11 :     uint256 shorttxidhash;
      39          11 :     hasher.Finalize(shorttxidhash.begin());
      40          11 :     shorttxidk0 = shorttxidhash.GetUint64(0);
      41          11 :     shorttxidk1 = shorttxidhash.GetUint64(1);
      42          11 : }
      43             : 
      44          12 : uint64_t CBlockHeaderAndShortTxIDs::GetShortID(const uint256& txhash) const {
      45             :     static_assert(SHORTTXIDS_LENGTH == 6, "shorttxids calculation assumes 6-byte shorttxids");
      46          12 :     return SipHashUint256(shorttxidk0, shorttxidk1, txhash) & 0xffffffffffffL;
      47             : }
      48             : 
      49             : 
      50             : 
      51           4 : ReadStatus PartiallyDownloadedBlock::InitData(const CBlockHeaderAndShortTxIDs& cmpctblock, const std::vector<std::pair<uint256, CTransactionRef>>& extra_txn) {
      52           4 :     if (cmpctblock.header.IsNull() || (cmpctblock.shorttxids.empty() && cmpctblock.prefilledtxn.empty()))
      53           0 :         return READ_STATUS_INVALID;
      54           4 :     if (cmpctblock.shorttxids.size() + cmpctblock.prefilledtxn.size() > MaxBlockSize() / MIN_TRANSACTION_SIZE)
      55           0 :         return READ_STATUS_INVALID;
      56             : 
      57           4 :     assert(header.IsNull() && txn_available.empty());
      58           4 :     header = cmpctblock.header;
      59           4 :     txn_available.resize(cmpctblock.BlockTxCount());
      60             : 
      61           4 :     int32_t lastprefilledindex = -1;
      62           9 :     for (size_t i = 0; i < cmpctblock.prefilledtxn.size(); i++) {
      63           5 :         if (cmpctblock.prefilledtxn[i].tx->IsNull())
      64           0 :             return READ_STATUS_INVALID;
      65             : 
      66           5 :         lastprefilledindex += cmpctblock.prefilledtxn[i].index + 1; //index is a uint16_t, so can't overflow here
      67           5 :         if (lastprefilledindex > std::numeric_limits<uint16_t>::max())
      68           0 :             return READ_STATUS_INVALID;
      69           5 :         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             :         }
      75           5 :         txn_available[lastprefilledindex] = cmpctblock.prefilledtxn[i].tx;
      76           5 :     }
      77           4 :     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           4 :     std::unordered_map<uint64_t, uint16_t> shorttxids(cmpctblock.shorttxids.size());
      84           4 :     uint16_t index_offset = 0;
      85           9 :     for (size_t i = 0; i < cmpctblock.shorttxids.size(); i++) {
      86           8 :         while (txn_available[i + index_offset])
      87           3 :             index_offset++;
      88           5 :         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           5 :         if (shorttxids.bucket_size(shorttxids.bucket(cmpctblock.shorttxids[i])) > 12)
     100           0 :             return READ_STATUS_FAILED;
     101           5 :     }
     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           4 :     if (shorttxids.size() != cmpctblock.shorttxids.size())
     105           0 :         return READ_STATUS_FAILED; // Short ID collision
     106             : 
     107           4 :     std::vector<bool> have_txn(txn_available.size());
     108             :     {
     109           4 :     LOCK(pool->cs);
     110           6 :     for (size_t i = 0; i < pool->vTxHashes.size(); i++) {
     111           3 :         uint64_t shortid = cmpctblock.GetShortID(pool->vTxHashes[i].first);
     112           3 :         std::unordered_map<uint64_t, uint16_t>::iterator idit = shorttxids.find(shortid);
     113           3 :         if (idit != shorttxids.end()) {
     114           3 :             if (!have_txn[idit->second]) {
     115           3 :                 txn_available[idit->second] = pool->vTxHashes[i].second->GetSharedTx();
     116           3 :                 have_txn[idit->second]  = true;
     117           3 :                 mempool_count++;
     118           3 :             } 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           3 :         }
     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           3 :         if (mempool_count == shorttxids.size())
     132           1 :             break;
     133           2 :     }
     134           4 :     }
     135             : 
     136           4 :     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 hashes first
     152           0 :                 if (txn_available[idit->second] &&
     153           0 :                         txn_available[idit->second]->GetHash() != extra_txn[i].second->GetHash()) {
     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           4 :     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           4 :     return READ_STATUS_OK;
     170           4 : }
     171             : 
     172          10 : bool PartiallyDownloadedBlock::IsTxAvailable(size_t index) const {
     173          10 :     assert(!header.IsNull());
     174          10 :     assert(index < txn_available.size());
     175          10 :     return txn_available[index] != nullptr;
     176             : }
     177             : 
     178           8 : ReadStatus PartiallyDownloadedBlock::FillBlock(CBlock& block, const std::vector<CTransactionRef>& vtx_missing) {
     179           8 :     assert(!header.IsNull());
     180           8 :     uint256 hash = header.GetHash();
     181           8 :     block = header;
     182           8 :     block.vtx.resize(txn_available.size());
     183             : 
     184           8 :     size_t tx_missing_offset = 0;
     185          25 :     for (size_t i = 0; i < txn_available.size(); i++) {
     186          19 :         if (!txn_available[i]) {
     187           6 :             if (vtx_missing.size() <= tx_missing_offset)
     188           2 :                 return READ_STATUS_INVALID;
     189           4 :             block.vtx[i] = vtx_missing[tx_missing_offset++];
     190           4 :         } else
     191          13 :             block.vtx[i] = std::move(txn_available[i]);
     192          17 :     }
     193             : 
     194             :     // Make sure we can't call FillBlock again.
     195           6 :     header.SetNull();
     196           6 :     txn_available.clear();
     197             : 
     198           6 :     if (vtx_missing.size() != tx_missing_offset)
     199           0 :         return READ_STATUS_INVALID;
     200             : 
     201           6 :     BlockValidationState state;
     202           6 :     if (!CheckBlock(block, state, Params().GetConsensus())) {
     203             :         // TODO: We really want to just check merkle tree manually here,
     204             :         // but that is expensive, and CheckBlock caches a block's
     205             :         // "checked-status" (in the CBlock?). CBlock should be able to
     206             :         // check its own merkle root and cache that check.
     207           2 :         if (state.GetResult() == BlockValidationResult::BLOCK_MUTATED)
     208           2 :             return READ_STATUS_FAILED; // Possible Short ID collision
     209           0 :         return READ_STATUS_CHECKBLOCK_FAILED;
     210             :     }
     211             : 
     212           4 :     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());
     213           4 :     if (vtx_missing.size() < 5) {
     214           6 :         for (const auto& tx : vtx_missing) {
     215           2 :             LogPrint(BCLog::CMPCTBLOCK, "Reconstructed block %s required tx %s\n", hash.ToString(), tx->GetHash().ToString());
     216             :         }
     217           4 :     }
     218             : 
     219           4 :     return READ_STATUS_OK;
     220           8 : }