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1 : : // Copyright (c) 2016-present 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 : :
18 : : #include <unordered_map>
19 : :
20 : 4719 : CBlockHeaderAndShortTxIDs::CBlockHeaderAndShortTxIDs(const CBlock& block, uint64_t nonce)
21 : 4719 : : nonce(nonce),
22 [ - + ]: 4719 : shorttxids(block.vtx.size() - 1),
23 [ + - ]: 4719 : prefilledtxn(1),
24 [ - + ]: 4719 : header(block)
25 : : {
26 [ + - ]: 4719 : FillShortTxIDSelector();
27 : : // TODO: Use our mempool prior to block acceptance to predictively fill more than just the coinbase
28 [ - + ]: 4719 : prefilledtxn[0] = {0, block.vtx[0]};
29 [ - + + + ]: 2206343 : for (size_t i = 1; i < block.vtx.size(); i++) {
30 [ + - ]: 2201624 : const CTransaction& tx = *block.vtx[i];
31 [ + - ]: 2201624 : shorttxids[i - 1] = GetShortID(tx.GetWitnessHash());
32 : : }
33 [ + - ]: 14157 : }
34 : :
35 : 9646 : void CBlockHeaderAndShortTxIDs::FillShortTxIDSelector() const
36 : : {
37 : 9646 : DataStream stream{};
38 [ + - + - ]: 9646 : stream << header << nonce;
39 [ + - ]: 9646 : CSHA256 hasher;
40 [ + - ]: 9646 : hasher.Write((unsigned char*)&(*stream.begin()), stream.end() - stream.begin());
41 : 9646 : uint256 shorttxidhash;
42 [ + - ]: 9646 : hasher.Finalize(shorttxidhash.begin());
43 : 9646 : m_hasher.emplace(shorttxidhash.GetUint64(0), shorttxidhash.GetUint64(1));
44 : 9646 : }
45 : :
46 : 2207386 : uint64_t CBlockHeaderAndShortTxIDs::GetShortID(const Wtxid& wtxid) const
47 : : {
48 : 2207386 : static_assert(SHORTTXIDS_LENGTH == 6, "shorttxids calculation assumes 6-byte shorttxids");
49 [ - + ]: 2207386 : return (*Assert(m_hasher))(wtxid.ToUint256()) & 0xffffffffffffL;
50 : : }
51 : :
52 : : /* Reconstructing a compact block is in the hot-path for block relay,
53 : : * so we want to do it as quickly as possible. Because this often
54 : : * involves iterating over the entire mempool, we put all the data we
55 : : * need (ie the wtxid and a reference to the actual transaction data)
56 : : * in a vector and iterate over the vector directly. This allows optimal
57 : : * CPU caching behaviour, at a cost of only 40 bytes per transaction.
58 : : */
59 : 819 : ReadStatus PartiallyDownloadedBlock::InitData(const CBlockHeaderAndShortTxIDs& cmpctblock, const std::vector<std::pair<Wtxid, CTransactionRef>>& extra_txn)
60 : : {
61 [ - + - - ]: 819 : LogDebug(BCLog::CMPCTBLOCK, "Initializing PartiallyDownloadedBlock for block %s using a cmpctblock of %u bytes\n", cmpctblock.header.GetHash().ToString(), GetSerializeSize(cmpctblock));
62 [ + + + + : 819 : if (cmpctblock.header.IsNull() || (cmpctblock.shorttxids.empty() && cmpctblock.prefilledtxn.empty()))
+ - ]
63 : : return READ_STATUS_INVALID;
64 [ - + - + : 798 : if (cmpctblock.shorttxids.size() + cmpctblock.prefilledtxn.size() > MAX_BLOCK_WEIGHT / MIN_SERIALIZABLE_TRANSACTION_WEIGHT)
+ - ]
65 : : return READ_STATUS_INVALID;
66 : :
67 [ + - + - ]: 798 : if (!header.IsNull() || !txn_available.empty()) return READ_STATUS_INVALID;
68 : :
69 : 798 : header = cmpctblock.header;
70 [ - + ]: 798 : txn_available.resize(cmpctblock.BlockTxCount());
71 : :
72 : 798 : int32_t lastprefilledindex = -1;
73 [ - + + + ]: 1526 : for (size_t i = 0; i < cmpctblock.prefilledtxn.size(); i++) {
74 [ + + ]: 798 : if (cmpctblock.prefilledtxn[i].tx->IsNull())
75 : : return READ_STATUS_INVALID;
76 : :
77 : 728 : lastprefilledindex += cmpctblock.prefilledtxn[i].index + 1; //index is a uint16_t, so can't overflow here
78 [ + - ]: 728 : if (lastprefilledindex > std::numeric_limits<uint16_t>::max())
79 : : return READ_STATUS_INVALID;
80 [ - + + - ]: 728 : if ((uint32_t)lastprefilledindex > cmpctblock.shorttxids.size() + i) {
81 : : // If we are inserting a tx at an index greater than our full list of shorttxids
82 : : // plus the number of prefilled txn we've inserted, then we have txn for which we
83 : : // have neither a prefilled txn or a shorttxid!
84 : : return READ_STATUS_INVALID;
85 : : }
86 : 728 : txn_available[lastprefilledindex] = cmpctblock.prefilledtxn[i].tx;
87 : : }
88 : 728 : prefilled_count = cmpctblock.prefilledtxn.size();
89 : :
90 : : // Calculate map of txids -> positions and check mempool to see what we have (or don't)
91 : : // Because well-formed cmpctblock messages will have a (relatively) uniform distribution
92 : : // of short IDs, any highly-uneven distribution of elements can be safely treated as a
93 : : // READ_STATUS_FAILED.
94 [ - + ]: 728 : std::unordered_map<uint64_t, uint16_t> shorttxids(cmpctblock.shorttxids.size());
95 : : uint16_t index_offset = 0;
96 [ - + + + ]: 2133969 : for (size_t i = 0; i < cmpctblock.shorttxids.size(); i++) {
97 [ + + ]: 2133970 : while (txn_available[i + index_offset])
98 : 726 : index_offset++;
99 [ + - ]: 2133244 : shorttxids[cmpctblock.shorttxids[i]] = i + index_offset;
100 : : // To determine the chance that the number of entries in a bucket exceeds N,
101 : : // we use the fact that the number of elements in a single bucket is
102 : : // binomially distributed (with n = the number of shorttxids S, and p =
103 : : // 1 / the number of buckets), that in the worst case the number of buckets is
104 : : // equal to S (due to std::unordered_map having a default load factor of 1.0),
105 : : // and that the chance for any bucket to exceed N elements is at most
106 : : // buckets * (the chance that any given bucket is above N elements).
107 : : // Thus: P(max_elements_per_bucket > N) <= S * (1 - cdf(binomial(n=S,p=1/S), N)).
108 : : // If we assume blocks of up to 16000, allowing 12 elements per bucket should
109 : : // only fail once per ~1 million block transfers (per peer and connection).
110 [ + + ]: 2133244 : if (shorttxids.bucket_size(shorttxids.bucket(cmpctblock.shorttxids[i])) > 12)
111 : : return READ_STATUS_FAILED;
112 : : }
113 [ + + ]: 725 : if (shorttxids.size() != cmpctblock.shorttxids.size())
114 : : return READ_STATUS_FAILED; // Short ID collision
115 : :
116 [ - + + - : 164 : std::vector<bool> have_txn(txn_available.size());
+ - ]
117 : 82 : {
118 [ + - ]: 82 : LOCK(pool->cs);
119 [ + - + + ]: 1399 : for (const auto& [wtxid, txit] : pool->txns_randomized) {
120 [ + - ]: 1320 : uint64_t shortid = cmpctblock.GetShortID(wtxid);
121 : 1320 : std::unordered_map<uint64_t, uint16_t>::iterator idit = shorttxids.find(shortid);
122 [ + - ]: 1320 : if (idit != shorttxids.end()) {
123 [ + - ]: 1320 : if (!have_txn[idit->second]) {
124 [ + - - + ]: 2640 : txn_available[idit->second] = txit->GetSharedTx();
125 : 1320 : have_txn[idit->second] = true;
126 : 1320 : mempool_count++;
127 : : } else {
128 : : // If we find two mempool txn that match the short id, just request it.
129 : : // This should be rare enough that the extra bandwidth doesn't matter,
130 : : // but eating a round-trip due to FillBlock failure would be annoying
131 [ # # ]: 0 : if (txn_available[idit->second]) {
132 : 0 : txn_available[idit->second].reset();
133 : 0 : mempool_count--;
134 : : }
135 : : }
136 : : }
137 : : // Though ideally we'd continue scanning for the two-txn-match-shortid case,
138 : : // the performance win of an early exit here is too good to pass up and worth
139 : : // the extra risk.
140 [ + + ]: 1320 : if (mempool_count == shorttxids.size())
141 : : break;
142 : : }
143 : 0 : }
144 : :
145 [ - + + + ]: 4510 : for (size_t i = 0; i < extra_txn.size(); i++) {
146 [ + - ]: 4442 : uint64_t shortid = cmpctblock.GetShortID(extra_txn[i].first);
147 : 4442 : std::unordered_map<uint64_t, uint16_t>::iterator idit = shorttxids.find(shortid);
148 [ + - ]: 4442 : if (idit != shorttxids.end()) {
149 [ + + ]: 4442 : if (!have_txn[idit->second]) {
150 : 3206 : txn_available[idit->second] = extra_txn[i].second;
151 : 3206 : have_txn[idit->second] = true;
152 : 3206 : mempool_count++;
153 : 3206 : extra_count++;
154 : : } else {
155 : : // If we find two mempool/extra txn that match the short id, just
156 : : // request it.
157 : : // This should be rare enough that the extra bandwidth doesn't matter,
158 : : // but eating a round-trip due to FillBlock failure would be annoying
159 : : // Note that we don't want duplication between extra_txn and mempool to
160 : : // trigger this case, so we compare witness hashes first
161 [ + - - + ]: 1236 : if (txn_available[idit->second] &&
162 [ + - - + ]: 1236 : txn_available[idit->second]->GetWitnessHash() != extra_txn[i].second->GetWitnessHash()) {
163 : 0 : txn_available[idit->second].reset();
164 : 0 : mempool_count--;
165 : 0 : extra_count--;
166 : : }
167 : : }
168 : : }
169 : : // Though ideally we'd continue scanning for the two-txn-match-shortid case,
170 : : // the performance win of an early exit here is too good to pass up and worth
171 : : // the extra risk.
172 [ + + ]: 4442 : if (mempool_count == shorttxids.size())
173 : : break;
174 : : }
175 : :
176 [ + - - + : 82 : LogDebug(BCLog::CMPCTBLOCK, "Initialized PartiallyDownloadedBlock for block %s using a cmpctblock of %u bytes\n", cmpctblock.header.GetHash().ToString(), GetSerializeSize(cmpctblock));
- - - - -
- - - ]
177 : :
178 : 82 : return READ_STATUS_OK;
179 : 810 : }
180 : :
181 : 4410871 : bool PartiallyDownloadedBlock::IsTxAvailable(size_t index) const
182 : : {
183 [ + + ]: 4410871 : if (header.IsNull()) return false;
184 : :
185 [ - + - + ]: 4408815 : assert(index < txn_available.size());
186 : 4408815 : return txn_available[index] != nullptr;
187 : : }
188 : :
189 : 819 : ReadStatus PartiallyDownloadedBlock::FillBlock(CBlock& block, const std::vector<CTransactionRef>& vtx_missing, bool segwit_active)
190 : : {
191 [ + + ]: 819 : if (header.IsNull()) return READ_STATUS_INVALID;
192 : :
193 : 798 : block = header;
194 [ - + ]: 798 : block.vtx.resize(txn_available.size());
195 : :
196 : 798 : size_t tx_missing_offset = 0;
197 [ - + + + ]: 1542208 : for (size_t i = 0; i < txn_available.size(); i++) {
198 [ + + ]: 1541867 : if (!txn_available[i]) {
199 [ - + + + ]: 1538659 : if (tx_missing_offset >= vtx_missing.size()) {
200 : : return READ_STATUS_INVALID;
201 : : }
202 : 1538202 : block.vtx[i] = vtx_missing[tx_missing_offset++];
203 : : } else {
204 : 3208 : block.vtx[i] = std::move(txn_available[i]);
205 : : }
206 : : }
207 : :
208 : : // Make sure we can't call FillBlock again.
209 : 341 : header.SetNull();
210 : 341 : txn_available.clear();
211 : :
212 [ - + + - ]: 341 : if (vtx_missing.size() != tx_missing_offset) {
213 : : return READ_STATUS_INVALID;
214 : : }
215 : :
216 : : // Check for possible mutations early now that we have a seemingly good block
217 [ + - ]: 341 : IsBlockMutatedFn check_mutated{m_check_block_mutated_mock ? m_check_block_mutated_mock : IsBlockMutated};
218 [ + - + + ]: 341 : if (check_mutated(/*block=*/block, /*check_witness_root=*/segwit_active)) {
219 : : return READ_STATUS_FAILED; // Possible Short ID collision
220 : : }
221 : :
222 [ + - - + ]: 330 : if (LogAcceptCategory(BCLog::CMPCTBLOCK, BCLog::Level::Debug)) {
223 [ # # ]: 0 : const uint256 hash{block.GetHash()};
224 : 0 : uint32_t tx_missing_size{0};
225 [ # # # # ]: 0 : for (const auto& tx : vtx_missing) tx_missing_size += tx->ComputeTotalSize();
226 [ # # # # : 0 : LogDebug(BCLog::CMPCTBLOCK, "Successfully reconstructed block %s with %u txn prefilled, %u txn from mempool (incl at least %u from extra pool) and %u txn (%u bytes) requested\n", hash.ToString(), prefilled_count, mempool_count, extra_count, vtx_missing.size(), tx_missing_size);
# # # # #
# ]
227 [ # # # # ]: 0 : if (vtx_missing.size() < 5) {
228 [ # # ]: 0 : for (const auto& tx : vtx_missing) {
229 [ # # # # : 0 : LogDebug(BCLog::CMPCTBLOCK, "Reconstructed block %s required tx %s\n", hash.ToString(), tx->GetHash().ToString());
# # # # #
# ]
230 : : }
231 : : }
232 : : }
233 : :
234 : : return READ_STATUS_OK;
235 : 341 : }
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