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1 : : // Copyright (c) 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 : : #ifndef BITCOIN_TEST_UTIL_CLUSTER_LINEARIZE_H
6 : : #define BITCOIN_TEST_UTIL_CLUSTER_LINEARIZE_H
7 : :
8 : : #include <cluster_linearize.h>
9 : : #include <serialize.h>
10 : : #include <span.h>
11 : : #include <streams.h>
12 : : #include <util/bitset.h>
13 : : #include <util/feefrac.h>
14 : :
15 : : #include <stdint.h>
16 : : #include <numeric>
17 : : #include <vector>
18 : : #include <utility>
19 : :
20 : : namespace {
21 : :
22 : : using namespace cluster_linearize;
23 : :
24 : : using TestBitSet = BitSet<32>;
25 : :
26 : : /** Check if a graph is acyclic. */
27 : : template<typename SetType>
28 : : bool IsAcyclic(const DepGraph<SetType>& depgraph) noexcept
29 : : {
30 : : for (ClusterIndex i : depgraph.Positions()) {
31 : : if ((depgraph.Ancestors(i) & depgraph.Descendants(i)) != SetType::Singleton(i)) {
32 : : return false;
33 : : }
34 : : }
35 : : return true;
36 : : }
37 : :
38 : : /** A formatter for a bespoke serialization for acyclic DepGraph objects.
39 : : *
40 : : * The serialization format outputs information about transactions in a topological order (parents
41 : : * before children), together with position information so transactions can be moved back to their
42 : : * correct position on deserialization.
43 : : *
44 : : * - For each transaction t in the DepGraph (in some topological order);
45 : : * - The size: VARINT(t.size), which cannot be 0.
46 : : * - The fee: VARINT(SignedToUnsigned(t.fee)), see below for SignedToUnsigned.
47 : : * - For each direct dependency:
48 : : * - VARINT(skip)
49 : : * - The position of t in the cluster: VARINT(skip)
50 : : * - The end of the graph: VARINT(0)
51 : : *
52 : : * The list of skip values encodes the dependencies of t, as well as its position in the cluster.
53 : : * Each skip value is the number of possibilities that were available, but were not taken. These
54 : : * possibilities are, in order:
55 : : * - For each previous transaction in the graph, in reverse serialization order, whether it is a
56 : : * direct parent of t (but excluding transactions which are already implied to be dependencies
57 : : * by parent relations that were serialized before it).
58 : : * - The various insertion positions in the cluster, from the very end of the cluster, to the
59 : : * front.
60 : : * - The appending of 1, 2, 3, ... holes at the end of the cluster, followed by appending the new
61 : : * transaction.
62 : : *
63 : : * Let's say you have a 7-transaction cluster, consisting of transactions F,A,C,B,_,G,E,_,D
64 : : * (where _ represent holes; unused positions within the DepGraph) but serialized in order
65 : : * A,B,C,D,E,F,G, because that happens to be a topological ordering. By the time G gets serialized,
66 : : * what has been serialized already represents the cluster F,A,C,B,_,E,_,D (in that order). G has B
67 : : * and E as direct parents, and E depends on C.
68 : : *
69 : : * In this case, the possibilities are, in order:
70 : : * - [ ] the dependency G->F
71 : : * - [X] the dependency G->E
72 : : * - [ ] the dependency G->D
73 : : * - [X] the dependency G->B
74 : : * - [ ] the dependency G->A
75 : : * - [ ] put G at the end of the cluster
76 : : * - [ ] put G before D
77 : : * - [ ] put G before the hole before D
78 : : * - [X] put G before E
79 : : * - [ ] put G before the hole before E
80 : : * - [ ] put G before B
81 : : * - [ ] put G before C
82 : : * - [ ] put G before A
83 : : * - [ ] put G before F
84 : : * - [ ] add 1 hole at the end of the cluster, followed by G
85 : : * - [ ] add 2 holes at the end of the cluster, followed by G
86 : : * - [ ] add ...
87 : : *
88 : : * The skip values in this case are 1 (G->F), 1 (G->D), 4 (G->A, G at end, G before D, G before
89 : : * hole). No skip after 4 is needed (or permitted), because there can only be one position for G.
90 : : * Also note that G->C is not included in the list of possibilities, as it is implied by the
91 : : * included G->E and E->C that came before it. On deserialization, if the last skip value was 8 or
92 : : * larger (putting G before the beginning of the cluster), it is interpreted as wrapping around
93 : : * back to the end.
94 : : *
95 : : *
96 : : * Rationale:
97 : : * - Why VARINTs? They are flexible enough to represent large numbers where needed, but more
98 : : * compact for smaller numbers. The serialization format is designed so that simple structures
99 : : * involve smaller numbers, so smaller size maps to simpler graphs.
100 : : * - Why use SignedToUnsigned? It results in small unsigned values for signed values with small
101 : : * absolute value. This way we can encode negative fees in graphs, but still let small negative
102 : : * numbers have small encodings.
103 : : * - Why are the parents emitted in reverse order compared to the transactions themselves? This
104 : : * naturally lets us skip parents-of-parents, as they will be reflected as implied dependencies.
105 : : * - Why encode skip values and not a bitmask to convey the list positions? It turns out that the
106 : : * most complex graphs (in terms of linearization complexity) are ones with ~1 dependency per
107 : : * transaction. The current encoding uses ~1 byte per transaction for dependencies in this case,
108 : : * while a bitmask would require ~N/2 bits per transaction.
109 : : */
110 : :
111 : : struct DepGraphFormatter
112 : : {
113 : : /** Convert x>=0 to 2x (even), x<0 to -2x-1 (odd). */
114 : 20 : [[maybe_unused]] static uint64_t SignedToUnsigned(int64_t x) noexcept
115 : : {
116 : 20 : if (x < 0) {
117 : 3 : return 2 * uint64_t(-(x + 1)) + 1;
118 : : } else {
119 : 17 : return 2 * uint64_t(x);
120 : : }
121 : : }
122 : :
123 : : /** Convert even x to x/2 (>=0), odd x to -(x/2)-1 (<0). */
124 : 20 : [[maybe_unused]] static int64_t UnsignedToSigned(uint64_t x) noexcept
125 : : {
126 : 20 : if (x & 1) {
127 : 3 : return -int64_t(x / 2) - 1;
128 : : } else {
129 : 17 : return int64_t(x / 2);
130 : : }
131 : : }
132 : :
133 : : template <typename Stream, typename SetType>
134 : 7 : static void Ser(Stream& s, const DepGraph<SetType>& depgraph)
135 : : {
136 : : /** Construct a topological order to serialize the transactions in. */
137 [ + - ]: 7 : std::vector<ClusterIndex> topo_order;
138 [ + - ]: 7 : topo_order.reserve(depgraph.TxCount());
139 [ + + + - : 33 : for (auto i : depgraph.Positions()) topo_order.push_back(i);
+ + ]
140 : 7 : std::sort(topo_order.begin(), topo_order.end(), [&](ClusterIndex a, ClusterIndex b) {
141 [ + + ]: 31 : auto anc_a = depgraph.Ancestors(a).Count(), anc_b = depgraph.Ancestors(b).Count();
142 [ + + ]: 31 : if (anc_a != anc_b) return anc_a < anc_b;
143 : 7 : return a < b;
144 : : });
145 : :
146 : : /** Which positions (incl. holes) the deserializer already knows when it has deserialized
147 : : * what has been serialized here so far. */
148 : 7 : SetType done;
149 : :
150 : : // Loop over the transactions in topological order.
151 [ + + ]: 27 : for (ClusterIndex topo_idx = 0; topo_idx < topo_order.size(); ++topo_idx) {
152 : : /** Which depgraph index we are currently writing. */
153 [ + - ]: 20 : ClusterIndex idx = topo_order[topo_idx];
154 : : // Write size, which must be larger than 0.
155 [ + - + + ]: 40 : s << VARINT_MODE(depgraph.FeeRate(idx).size, VarIntMode::NONNEGATIVE_SIGNED);
156 : : // Write fee, encoded as an unsigned varint (odd=negative, even=non-negative).
157 [ + + + - ]: 40 : s << VARINT(SignedToUnsigned(depgraph.FeeRate(idx).fee));
158 : : // Write dependency information.
159 : 20 : SetType written_parents;
160 : 20 : uint64_t diff = 0; //!< How many potential parent/child relations we have skipped over.
161 [ + + ]: 50 : for (ClusterIndex dep_dist = 0; dep_dist < topo_idx; ++dep_dist) {
162 : : /** Which depgraph index we are currently considering as parent of idx. */
163 [ + + ]: 30 : ClusterIndex dep_idx = topo_order[topo_idx - 1 - dep_dist];
164 : : // Ignore transactions which are already known to be ancestors.
165 [ + + ]: 30 : if (depgraph.Descendants(dep_idx).Overlaps(written_parents)) continue;
166 [ + + ]: 25 : if (depgraph.Ancestors(idx)[dep_idx]) {
167 : : // When an actual parent is encountered, encode how many non-parents were skipped
168 : : // before it.
169 [ + - ]: 14 : s << VARINT(diff);
170 : 14 : diff = 0;
171 : 14 : written_parents.Set(dep_idx);
172 : : } else {
173 : : // When a non-parent is encountered, increment the skip counter.
174 : 11 : ++diff;
175 : : }
176 : : }
177 : : // Write position information.
178 [ + + ]: 20 : auto add_holes = SetType::Fill(idx) - done - depgraph.Positions();
179 [ + + ]: 20 : if (add_holes.None()) {
180 : : // The new transaction is to be inserted N positions back from the end of the
181 : : // cluster. Emit N to indicate that that many insertion choices are skipped.
182 [ + - ]: 17 : auto skips = (done - SetType::Fill(idx)).Count();
183 [ + - ]: 17 : s << VARINT(diff + skips);
184 : : } else {
185 : : // The new transaction is to be appended at the end of the cluster, after N holes.
186 : : // Emit current_cluster_size + N, to indicate all insertion choices are skipped,
187 : : // plus N possibilities for the number of holes.
188 [ + - ]: 6 : s << VARINT(diff + done.Count() + add_holes.Count());
189 : 3 : done |= add_holes;
190 : : }
191 : 20 : done.Set(idx);
192 : : }
193 : :
194 : : // Output a final 0 to denote the end of the graph.
195 [ + - ]: 14 : s << uint8_t{0};
196 : 7 : }
197 : :
198 : : template <typename Stream, typename SetType>
199 : 7 : void Unser(Stream& s, DepGraph<SetType>& depgraph)
200 : : {
201 : : /** The dependency graph which we deserialize into first, with transactions in
202 : : * topological serialization order, not original cluster order. */
203 : 7 : DepGraph<SetType> topo_depgraph;
204 : : /** Mapping from serialization order to cluster order, used later to reconstruct the
205 : : * cluster order. */
206 : 7 : std::vector<ClusterIndex> reordering;
207 : : /** How big the entries vector in the reconstructed depgraph will be (including holes). */
208 : 7 : ClusterIndex total_size{0};
209 : :
210 : : // Read transactions in topological order.
211 : : while (true) {
212 : 27 : FeeFrac new_feerate; //!< The new transaction's fee and size.
213 : 27 : SetType new_ancestors; //!< The new transaction's ancestors (excluding itself).
214 : 27 : uint64_t diff{0}; //!< How many potential parents/insertions we have to skip.
215 [ + - ]: 27 : bool read_error{false};
216 : : try {
217 : : // Read size. Size 0 signifies the end of the DepGraph.
218 : : int32_t size;
219 [ + - ]: 27 : s >> VARINT_MODE(size, VarIntMode::NONNEGATIVE_SIGNED);
220 : 27 : size &= 0x3FFFFF; // Enough for size up to 4M.
221 : : static_assert(0x3FFFFF >= 4000000);
222 [ + + + - ]: 27 : if (size == 0 || topo_depgraph.TxCount() == SetType::Size()) break;
223 : : // Read fee, encoded as an unsigned varint (odd=negative, even=non-negative).
224 : : uint64_t coded_fee;
225 [ + - ]: 20 : s >> VARINT(coded_fee);
226 : 20 : coded_fee &= 0xFFFFFFFFFFFFF; // Enough for fee between -21M...21M BTC.
227 : : static_assert(0xFFFFFFFFFFFFF > uint64_t{2} * 21000000 * 100000000);
228 [ + + + - ]: 40 : new_feerate = {UnsignedToSigned(coded_fee), size};
229 : : // Read dependency information.
230 [ + - ]: 20 : auto topo_idx = reordering.size();
231 [ + - ]: 20 : s >> VARINT(diff);
232 [ + + ]: 50 : for (ClusterIndex dep_dist = 0; dep_dist < topo_idx; ++dep_dist) {
233 : : /** Which topo_depgraph index we are currently considering as parent of topo_idx. */
234 : 30 : ClusterIndex dep_topo_idx = topo_idx - 1 - dep_dist;
235 : : // Ignore transactions which are already known ancestors of topo_idx.
236 [ + + ]: 30 : if (new_ancestors[dep_topo_idx]) continue;
237 [ + + ]: 25 : if (diff == 0) {
238 : : // When the skip counter has reached 0, add an actual dependency.
239 [ + - ]: 14 : new_ancestors |= topo_depgraph.Ancestors(dep_topo_idx);
240 : : // And read the number of skips after it.
241 [ + - ]: 44 : s >> VARINT(diff);
242 : : } else {
243 : : // Otherwise, dep_topo_idx is not a parent. Decrement and continue.
244 : 11 : --diff;
245 : : }
246 : : }
247 [ - - ]: 0 : } catch (const std::ios_base::failure&) {
248 : : // Continue even if a read error was encountered.
249 : 0 : read_error = true;
250 : : }
251 : : // Construct a new transaction whenever we made it past the new_feerate construction.
252 [ + - ]: 20 : if (new_feerate.IsEmpty()) break;
253 [ - + ]: 20 : assert(reordering.size() < SetType::Size());
254 : 20 : auto topo_idx = topo_depgraph.AddTransaction(new_feerate);
255 : 20 : topo_depgraph.AddDependencies(new_ancestors, topo_idx);
256 [ + - ]: 20 : if (total_size < SetType::Size()) {
257 : : // Normal case.
258 : 20 : diff %= SetType::Size();
259 [ + + ]: 20 : if (diff <= total_size) {
260 : : // Insert the new transaction at distance diff back from the end.
261 [ + + ]: 44 : for (auto& pos : reordering) {
262 : 27 : pos += (pos >= total_size - diff);
263 : : }
264 [ + - ]: 17 : reordering.push_back(total_size++ - diff);
265 : : } else {
266 : : // Append diff - total_size holes at the end, plus the new transaction.
267 : 3 : total_size = diff;
268 [ + - ]: 3 : reordering.push_back(total_size++);
269 : : }
270 : : } else {
271 : : // In case total_size == SetType::Size, it is not possible to insert the new
272 : : // transaction without exceeding SetType's size. Instead, interpret diff as an
273 : : // index into the holes, and overwrite a position there. This branch is never used
274 : : // when deserializing the output of the serializer, but gives meaning to otherwise
275 : : // invalid input.
276 : 0 : diff %= (SetType::Size() - reordering.size());
277 : 0 : SetType holes = SetType::Fill(SetType::Size());
278 [ # # ]: 0 : for (auto pos : reordering) holes.Reset(pos);
279 [ # # # # ]: 0 : for (auto pos : holes) {
280 [ # # ]: 0 : if (diff == 0) {
281 [ # # ]: 0 : reordering.push_back(pos);
282 : : break;
283 : : }
284 : 0 : --diff;
285 : : }
286 : : }
287 : : // Stop if a read error was encountered during deserialization.
288 [ + - ]: 20 : if (read_error) break;
289 : : }
290 : :
291 : : // Construct the original cluster order depgraph.
292 : 7 : depgraph = DepGraph(topo_depgraph, reordering, total_size);
293 : 7 : }
294 : : };
295 : :
296 : : /** Perform a sanity/consistency check on a DepGraph. */
297 : : template<typename SetType>
298 : : void SanityCheck(const DepGraph<SetType>& depgraph)
299 : : {
300 : : // Verify Positions and PositionRange consistency.
301 : : ClusterIndex num_positions{0};
302 : : ClusterIndex position_range{0};
303 : : for (ClusterIndex i : depgraph.Positions()) {
304 : : ++num_positions;
305 : : position_range = i + 1;
306 : : }
307 : : assert(num_positions == depgraph.TxCount());
308 : : assert(position_range == depgraph.PositionRange());
309 : : assert(position_range >= num_positions);
310 : : assert(position_range <= SetType::Size());
311 : : // Consistency check between ancestors internally.
312 : : for (ClusterIndex i : depgraph.Positions()) {
313 : : // Transactions include themselves as ancestors.
314 : : assert(depgraph.Ancestors(i)[i]);
315 : : // If a is an ancestor of b, then b's ancestors must include all of a's ancestors.
316 : : for (auto a : depgraph.Ancestors(i)) {
317 : : assert(depgraph.Ancestors(i).IsSupersetOf(depgraph.Ancestors(a)));
318 : : }
319 : : }
320 : : // Consistency check between ancestors and descendants.
321 : : for (ClusterIndex i : depgraph.Positions()) {
322 : : for (ClusterIndex j : depgraph.Positions()) {
323 : : assert(depgraph.Ancestors(i)[j] == depgraph.Descendants(j)[i]);
324 : : }
325 : : // No transaction is a parent or child of itself.
326 : : auto parents = depgraph.GetReducedParents(i);
327 : : auto children = depgraph.GetReducedChildren(i);
328 : : assert(!parents[i]);
329 : : assert(!children[i]);
330 : : // Parents of a transaction do not have ancestors inside those parents (except itself).
331 : : // Note that even the transaction itself may be missing (if it is part of a cycle).
332 : : for (auto parent : parents) {
333 : : assert((depgraph.Ancestors(parent) & parents).IsSubsetOf(SetType::Singleton(parent)));
334 : : }
335 : : // Similar for children and descendants.
336 : : for (auto child : children) {
337 : : assert((depgraph.Descendants(child) & children).IsSubsetOf(SetType::Singleton(child)));
338 : : }
339 : : }
340 : : if (IsAcyclic(depgraph)) {
341 : : // If DepGraph is acyclic, serialize + deserialize must roundtrip.
342 : : std::vector<unsigned char> ser;
343 : : VectorWriter writer(ser, 0);
344 : : writer << Using<DepGraphFormatter>(depgraph);
345 : : SpanReader reader(ser);
346 : : DepGraph<TestBitSet> decoded_depgraph;
347 : : reader >> Using<DepGraphFormatter>(decoded_depgraph);
348 : : assert(depgraph == decoded_depgraph);
349 : : assert(reader.empty());
350 : : // It must also deserialize correctly without the terminal 0 byte (as the deserializer
351 : : // will upon EOF still return what it read so far).
352 : : assert(ser.size() >= 1 && ser.back() == 0);
353 : : ser.pop_back();
354 : : reader = SpanReader{ser};
355 : : decoded_depgraph = {};
356 : : reader >> Using<DepGraphFormatter>(decoded_depgraph);
357 : : assert(depgraph == decoded_depgraph);
358 : : assert(reader.empty());
359 : :
360 : : // In acyclic graphs, the union of parents with parents of parents etc. yields the
361 : : // full ancestor set (and similar for children and descendants).
362 : : std::vector<SetType> parents(depgraph.PositionRange()), children(depgraph.PositionRange());
363 : : for (ClusterIndex i : depgraph.Positions()) {
364 : : parents[i] = depgraph.GetReducedParents(i);
365 : : children[i] = depgraph.GetReducedChildren(i);
366 : : }
367 : : for (auto i : depgraph.Positions()) {
368 : : // Initialize the set of ancestors with just the current transaction itself.
369 : : SetType ancestors = SetType::Singleton(i);
370 : : // Iteratively add parents of all transactions in the ancestor set to itself.
371 : : while (true) {
372 : : const auto old_ancestors = ancestors;
373 : : for (auto j : ancestors) ancestors |= parents[j];
374 : : // Stop when no more changes are being made.
375 : : if (old_ancestors == ancestors) break;
376 : : }
377 : : assert(ancestors == depgraph.Ancestors(i));
378 : :
379 : : // Initialize the set of descendants with just the current transaction itself.
380 : : SetType descendants = SetType::Singleton(i);
381 : : // Iteratively add children of all transactions in the descendant set to itself.
382 : : while (true) {
383 : : const auto old_descendants = descendants;
384 : : for (auto j : descendants) descendants |= children[j];
385 : : // Stop when no more changes are being made.
386 : : if (old_descendants == descendants) break;
387 : : }
388 : : assert(descendants == depgraph.Descendants(i));
389 : : }
390 : : }
391 : : }
392 : :
393 : : /** Perform a sanity check on a linearization. */
394 : : template<typename SetType>
395 : : void SanityCheck(const DepGraph<SetType>& depgraph, Span<const ClusterIndex> linearization)
396 : : {
397 : : // Check completeness.
398 : : assert(linearization.size() == depgraph.TxCount());
399 : : TestBitSet done;
400 : : for (auto i : linearization) {
401 : : // Check transaction position is in range.
402 : : assert(depgraph.Positions()[i]);
403 : : // Check topology and lack of duplicates.
404 : : assert((depgraph.Ancestors(i) - done) == TestBitSet::Singleton(i));
405 : : done.Set(i);
406 : : }
407 : : }
408 : :
409 : : } // namespace
410 : :
411 : : #endif // BITCOIN_TEST_UTIL_CLUSTER_LINEARIZE_H
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