Branch data Line data Source code
1 : : // Copyright (c) 2022-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 <headerssync.h>
6 : :
7 : : #include <logging.h>
8 : : #include <pow.h>
9 : : #include <util/check.h>
10 : : #include <util/time.h>
11 : : #include <util/vector.h>
12 : :
13 : : // Our memory analysis in headerssync-params.py assumes this many bytes for a
14 : : // CompressedHeader (we should re-calculate parameters if we compress further).
15 : : static_assert(sizeof(CompressedHeader) == 48);
16 : :
17 : 1142 : HeadersSyncState::HeadersSyncState(NodeId id,
18 : : const Consensus::Params& consensus_params,
19 : : const HeadersSyncParams& params,
20 : : const CBlockIndex& chain_start,
21 : 1142 : const arith_uint256& minimum_required_work)
22 [ - + ]: 2284 : : m_commit_offset((assert(params.commitment_period > 0), // HeadersSyncParams field must be initialized to non-zero.
23 : 1142 : FastRandomContext().randrange(params.commitment_period))),
24 : 1142 : m_id(id),
25 : 1142 : m_consensus_params(consensus_params),
26 : 1142 : m_params(params),
27 : 1142 : m_chain_start(chain_start),
28 : 1142 : m_minimum_required_work(minimum_required_work),
29 : 1142 : m_current_chain_work(chain_start.nChainWork),
30 : 1142 : m_last_header_received(m_chain_start.GetBlockHeader()),
31 [ + - ]: 1142 : m_current_height(chain_start.nHeight)
32 : : {
33 : : // Estimate the number of blocks that could possibly exist on the peer's
34 : : // chain *right now* using 6 blocks/second (fastest blockrate given the MTP
35 : : // rule) times the number of seconds from the last allowed block until
36 : : // today. This serves as a memory bound on how many commitments we might
37 : : // store from this peer, and we can safely give up syncing if the peer
38 : : // exceeds this bound, because it's not possible for a consensus-valid
39 : : // chain to be longer than this (at the current time -- in the future we
40 : : // could try again, if necessary, to sync a longer chain).
41 : 1142 : const auto max_seconds_since_start{(Ticks<std::chrono::seconds>(NodeClock::now() - NodeSeconds{std::chrono::seconds{chain_start.GetMedianTimePast()}}))
42 : 1142 : + MAX_FUTURE_BLOCK_TIME};
43 : 1142 : m_max_commitments = 6 * max_seconds_since_start / m_params.commitment_period;
44 : :
45 [ + - - + : 1142 : LogDebug(BCLog::NET, "Initial headers sync started with peer=%d: height=%i, max_commitments=%i, min_work=%s\n", m_id, m_current_height, m_max_commitments, m_minimum_required_work.ToString());
- - - - ]
46 : 1142 : }
47 : :
48 : : /** Free any memory in use, and mark this object as no longer usable. This is
49 : : * required to guarantee that we won't reuse this object with the same
50 : : * SaltedUint256Hasher for another sync. */
51 : 925 : void HeadersSyncState::Finalize()
52 : : {
53 [ - + ]: 925 : Assume(m_download_state != State::FINAL);
54 : 925 : ClearShrink(m_header_commitments);
55 : 925 : m_last_header_received.SetNull();
56 : 925 : ClearShrink(m_redownloaded_headers);
57 : 925 : m_redownload_buffer_last_hash.SetNull();
58 : 925 : m_redownload_buffer_first_prev_hash.SetNull();
59 : 925 : m_process_all_remaining_headers = false;
60 : 925 : m_current_height = 0;
61 : :
62 : 925 : m_download_state = State::FINAL;
63 : 925 : }
64 : :
65 : : /** Process the next batch of headers received from our peer.
66 : : * Validate and store commitments, and compare total chainwork to our target to
67 : : * see if we can switch to REDOWNLOAD mode. */
68 : 367246 : HeadersSyncState::ProcessingResult HeadersSyncState::ProcessNextHeaders(
69 : : std::span<const CBlockHeader> received_headers, const bool full_headers_message)
70 : : {
71 : 367246 : ProcessingResult ret;
72 : :
73 [ - + ]: 367246 : Assume(!received_headers.empty());
74 [ + - ]: 367246 : if (received_headers.empty()) return ret;
75 : :
76 [ - + ]: 367246 : Assume(m_download_state != State::FINAL);
77 [ + - ]: 367246 : if (m_download_state == State::FINAL) return ret;
78 : :
79 [ + + ]: 367246 : if (m_download_state == State::PRESYNC) {
80 : : // During PRESYNC, we minimally validate block headers and
81 : : // occasionally add commitments to them, until we reach our work
82 : : // threshold (at which point m_download_state is updated to REDOWNLOAD).
83 [ + - ]: 367038 : ret.success = ValidateAndStoreHeadersCommitments(received_headers);
84 [ + + ]: 367038 : if (ret.success) {
85 [ + + + + ]: 366263 : if (full_headers_message || m_download_state == State::REDOWNLOAD) {
86 : : // A full headers message means the peer may have more to give us;
87 : : // also if we just switched to REDOWNLOAD then we need to re-request
88 : : // headers from the beginning.
89 : 366175 : ret.request_more = true;
90 : : } else {
91 [ - + ]: 88 : Assume(m_download_state == State::PRESYNC);
92 : : // If we're in PRESYNC and we get a non-full headers
93 : : // message, then the peer's chain has ended and definitely doesn't
94 : : // have enough work, so we can stop our sync.
95 [ + - - + : 88 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: incomplete headers message at height=%i (presync phase)\n", m_id, m_current_height);
- - ]
96 : : }
97 : : }
98 [ + - ]: 208 : } else if (m_download_state == State::REDOWNLOAD) {
99 : : // During REDOWNLOAD, we compare our stored commitments to what we
100 : : // receive, and add headers to our redownload buffer. When the buffer
101 : : // gets big enough (meaning that we've checked enough commitments),
102 : : // we'll return a batch of headers to the caller for processing.
103 : 208 : ret.success = true;
104 [ + + ]: 6705 : for (const auto& hdr : received_headers) {
105 [ + - + + ]: 6509 : if (!ValidateAndStoreRedownloadedHeader(hdr)) {
106 : : // Something went wrong -- the peer gave us an unexpected chain.
107 : : // We could consider looking at the reason for failure and
108 : : // punishing the peer, but for now just give up on sync.
109 : 12 : ret.success = false;
110 : 12 : break;
111 : : }
112 : : }
113 : :
114 [ + + ]: 208 : if (ret.success) {
115 : : // Return any headers that are ready for acceptance.
116 [ + - ]: 196 : ret.pow_validated_headers = PopHeadersReadyForAcceptance();
117 : :
118 : : // If we hit our target blockhash, then all remaining headers will be
119 : : // returned and we can clear any leftover internal state.
120 [ + + + + ]: 196 : if (m_redownloaded_headers.empty() && m_process_all_remaining_headers) {
121 [ + - - + : 27 : LogDebug(BCLog::NET, "Initial headers sync complete with peer=%d: releasing all at height=%i (redownload phase)\n", m_id, m_redownload_buffer_last_height);
- - ]
122 [ + + ]: 169 : } else if (full_headers_message) {
123 : : // If the headers message is full, we need to request more.
124 : 146 : ret.request_more = true;
125 : : } else {
126 : : // For some reason our peer gave us a high-work chain, but is now
127 : : // declining to serve us that full chain again. Give up.
128 : : // Note that there's no more processing to be done with these
129 : : // headers, so we can still return success.
130 [ + - - + : 23 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: incomplete headers message at height=%i (redownload phase)\n", m_id, m_redownload_buffer_last_height);
- - ]
131 : : }
132 : : }
133 : : }
134 : :
135 [ + + + + : 367246 : if (!(ret.success && ret.request_more)) Finalize();
+ - ]
136 : : return ret;
137 : 0 : }
138 : :
139 : 367038 : bool HeadersSyncState::ValidateAndStoreHeadersCommitments(std::span<const CBlockHeader> headers)
140 : : {
141 : : // The caller should not give us an empty set of headers.
142 [ - + ]: 367038 : Assume(headers.size() > 0);
143 [ + - ]: 367038 : if (headers.size() == 0) return true;
144 : :
145 [ - + ]: 367038 : Assume(m_download_state == State::PRESYNC);
146 [ + - ]: 367038 : if (m_download_state != State::PRESYNC) return false;
147 : :
148 [ + + ]: 367038 : if (headers[0].hashPrevBlock != m_last_header_received.GetHash()) {
149 : : // Somehow our peer gave us a header that doesn't connect.
150 : : // This might be benign -- perhaps our peer reorged away from the chain
151 : : // they were on. Give up on this sync for now (likely we will start a
152 : : // new sync with a new starting point).
153 [ - + ]: 205 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: non-continuous headers at height=%i (presync phase)\n", m_id, m_current_height);
154 : 205 : return false;
155 : : }
156 : :
157 : : // If it does connect, (minimally) validate and occasionally store
158 : : // commitments.
159 [ + + ]: 860100 : for (const auto& hdr : headers) {
160 [ + + ]: 493837 : if (!ValidateAndProcessSingleHeader(hdr)) {
161 : : return false;
162 : : }
163 : : }
164 : :
165 [ + + ]: 366263 : if (m_current_chain_work >= m_minimum_required_work) {
166 : 78 : m_redownloaded_headers.clear();
167 : 78 : m_redownload_buffer_last_height = m_chain_start.nHeight;
168 : 78 : m_redownload_buffer_first_prev_hash = m_chain_start.GetBlockHash();
169 : 78 : m_redownload_buffer_last_hash = m_chain_start.GetBlockHash();
170 : 78 : m_redownload_chain_work = m_chain_start.nChainWork;
171 : 78 : m_download_state = State::REDOWNLOAD;
172 [ - + ]: 78 : LogDebug(BCLog::NET, "Initial headers sync transition with peer=%d: reached sufficient work at height=%i, redownloading from height=%i\n", m_id, m_current_height, m_redownload_buffer_last_height);
173 : : }
174 : : return true;
175 : : }
176 : :
177 : 493837 : bool HeadersSyncState::ValidateAndProcessSingleHeader(const CBlockHeader& current)
178 : : {
179 [ - + ]: 493837 : Assume(m_download_state == State::PRESYNC);
180 [ + - ]: 493837 : if (m_download_state != State::PRESYNC) return false;
181 : :
182 : 493837 : int next_height = m_current_height + 1;
183 : :
184 : : // Verify that the difficulty isn't growing too fast; an adversary with
185 : : // limited hashing capability has a greater chance of producing a high
186 : : // work chain if they compress the work into as few blocks as possible,
187 : : // so don't let anyone give a chain that would violate the difficulty
188 : : // adjustment maximum.
189 [ + + ]: 493837 : if (!PermittedDifficultyTransition(m_consensus_params, next_height,
190 : 493837 : m_last_header_received.nBits, current.nBits)) {
191 [ - + ]: 570 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: invalid difficulty transition at height=%i (presync phase)\n", m_id, next_height);
192 : 570 : return false;
193 : : }
194 : :
195 [ + + ]: 493267 : if (next_height % m_params.commitment_period == m_commit_offset) {
196 : : // Add a commitment.
197 : 7460 : m_header_commitments.push_back(m_hasher(current.GetHash()) & 1);
198 [ - + ]: 7460 : if (m_header_commitments.size() > m_max_commitments) {
199 : : // The peer's chain is too long; give up.
200 : : // It's possible the chain grew since we started the sync; so
201 : : // potentially we could succeed in syncing the peer's chain if we
202 : : // try again later.
203 [ # # ]: 0 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: exceeded max commitments at height=%i (presync phase)\n", m_id, next_height);
204 : 0 : return false;
205 : : }
206 : : }
207 : :
208 : 493267 : m_current_chain_work += GetBlockProof(current);
209 : 493267 : m_last_header_received = current;
210 : 493267 : m_current_height = next_height;
211 : :
212 : 493267 : return true;
213 : : }
214 : :
215 : 6509 : bool HeadersSyncState::ValidateAndStoreRedownloadedHeader(const CBlockHeader& header)
216 : : {
217 [ - + ]: 6509 : Assume(m_download_state == State::REDOWNLOAD);
218 [ + - ]: 6509 : if (m_download_state != State::REDOWNLOAD) return false;
219 : :
220 : 6509 : int64_t next_height = m_redownload_buffer_last_height + 1;
221 : :
222 : : // Ensure that we're working on a header that connects to the chain we're
223 : : // downloading.
224 [ + + ]: 6509 : if (header.hashPrevBlock != m_redownload_buffer_last_hash) {
225 [ - + ]: 10 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: non-continuous headers at height=%i (redownload phase)\n", m_id, next_height);
226 : 10 : return false;
227 : : }
228 : :
229 : : // Check that the difficulty adjustments are within our tolerance:
230 : 6499 : uint32_t previous_nBits{0};
231 [ + + ]: 6499 : if (!m_redownloaded_headers.empty()) {
232 : 6370 : previous_nBits = m_redownloaded_headers.back().nBits;
233 : : } else {
234 : 129 : previous_nBits = m_chain_start.nBits;
235 : : }
236 : :
237 [ + + ]: 6499 : if (!PermittedDifficultyTransition(m_consensus_params, next_height,
238 : 6499 : previous_nBits, header.nBits)) {
239 [ - + ]: 1 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: invalid difficulty transition at height=%i (redownload phase)\n", m_id, next_height);
240 : 1 : return false;
241 : : }
242 : :
243 : : // Track work on the redownloaded chain
244 : 6498 : m_redownload_chain_work += GetBlockProof(header);
245 : :
246 [ + + ]: 6498 : if (m_redownload_chain_work >= m_minimum_required_work) {
247 : 44 : m_process_all_remaining_headers = true;
248 : : }
249 : :
250 : : // If we're at a header for which we previously stored a commitment, verify
251 : : // it is correct. Failure will result in aborting download.
252 : : // Also, don't check commitments once we've gotten to our target blockhash;
253 : : // it's possible our peer has extended its chain between our first sync and
254 : : // our second, and we don't want to return failure after we've seen our
255 : : // target blockhash just because we ran out of commitments.
256 [ + + + + ]: 6498 : if (!m_process_all_remaining_headers && next_height % m_params.commitment_period == m_commit_offset) {
257 [ - + ]: 325 : if (m_header_commitments.size() == 0) {
258 [ # # ]: 0 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: commitment overrun at height=%i (redownload phase)\n", m_id, next_height);
259 : : // Somehow our peer managed to feed us a different chain and
260 : : // we've run out of commitments.
261 : 0 : return false;
262 : : }
263 : 325 : bool commitment = m_hasher(header.GetHash()) & 1;
264 : 325 : bool expected_commitment = m_header_commitments.front();
265 : 325 : m_header_commitments.pop_front();
266 [ + + ]: 325 : if (commitment != expected_commitment) {
267 [ - + ]: 1 : LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: commitment mismatch at height=%i (redownload phase)\n", m_id, next_height);
268 : 1 : return false;
269 : : }
270 : : }
271 : :
272 : : // Store this header for later processing.
273 : 6497 : m_redownloaded_headers.emplace_back(header);
274 : 6497 : m_redownload_buffer_last_height = next_height;
275 : 6497 : m_redownload_buffer_last_hash = header.GetHash();
276 : :
277 : 6497 : return true;
278 : : }
279 : :
280 : 196 : std::vector<CBlockHeader> HeadersSyncState::PopHeadersReadyForAcceptance()
281 : : {
282 : 196 : std::vector<CBlockHeader> ret;
283 : :
284 [ - + ]: 196 : Assume(m_download_state == State::REDOWNLOAD);
285 [ + - ]: 196 : if (m_download_state != State::REDOWNLOAD) return ret;
286 : :
287 [ - + + + : 2715 : while (m_redownloaded_headers.size() > m_params.redownload_buffer_size ||
+ + ]
288 [ + + + + ]: 1253 : (m_redownloaded_headers.size() > 0 && m_process_all_remaining_headers)) {
289 [ + - ]: 2519 : ret.emplace_back(m_redownloaded_headers.front().GetFullHeader(m_redownload_buffer_first_prev_hash));
290 : 2519 : m_redownloaded_headers.pop_front();
291 [ + - ]: 2519 : m_redownload_buffer_first_prev_hash = ret.back().GetHash();
292 : : }
293 : : return ret;
294 : 0 : }
295 : :
296 : 366321 : CBlockLocator HeadersSyncState::NextHeadersRequestLocator() const
297 : : {
298 [ - + ]: 366321 : Assume(m_download_state != State::FINAL);
299 [ - + ]: 366321 : if (m_download_state == State::FINAL) return {};
300 : :
301 : 366321 : auto chain_start_locator = LocatorEntries(&m_chain_start);
302 : 366321 : std::vector<uint256> locator;
303 : :
304 [ + + ]: 366321 : if (m_download_state == State::PRESYNC) {
305 : : // During pre-synchronization, we continue from the last header received.
306 [ + - ]: 366097 : locator.push_back(m_last_header_received.GetHash());
307 : : }
308 : :
309 [ + + ]: 366321 : if (m_download_state == State::REDOWNLOAD) {
310 : : // During redownload, we will download from the last received header that we stored.
311 [ + - ]: 224 : locator.push_back(m_redownload_buffer_last_hash);
312 : : }
313 : :
314 [ + - ]: 366321 : locator.insert(locator.end(), chain_start_locator.begin(), chain_start_locator.end());
315 : :
316 : 366321 : return CBlockLocator{std::move(locator)};
317 : 366321 : }
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