fuzz: Add fuzz target for ImprovesFeerateDiagram

Co-authored-by: Suhas Daftuar <sdaftuar@chaincode.com>

src/test/fuzz/rbf.cpp

@@ -23,12 +23,30 @@ namespace {
 const BasicTestingSetup* g_setup;
 } // namespace
 
+const int NUM_ITERS = 10000;
+
+std::vector<COutPoint> g_outpoints;
+
 void initialize_rbf()
 {
     static const auto testing_setup = MakeNoLogFileContext<>();
     g_setup = testing_setup.get();
 }
 
+void initialize_package_rbf()
+{
+    static const auto testing_setup = MakeNoLogFileContext<>();
+    g_setup = testing_setup.get();
+
+    // Create a fixed set of unique "UTXOs" to source parents from
+    // to avoid fuzzer giving circular references
+    for (int i = 0; i < NUM_ITERS; ++i) {
+        g_outpoints.emplace_back();
+        g_outpoints.back().n = i;
+    }
+
+}
+
 FUZZ_TARGET(rbf, .init = initialize_rbf)
 {
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
@@ -40,7 +58,7 @@ FUZZ_TARGET(rbf, .init = initialize_rbf)
 
     CTxMemPool pool{MemPoolOptionsForTest(g_setup->m_node)};
 
-    LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), 10000)
+    LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), NUM_ITERS)
     {
         const std::optional<CMutableTransaction> another_mtx = ConsumeDeserializable<CMutableTransaction>(fuzzed_data_provider, TX_WITH_WITNESS);
         if (!another_mtx) {
@@ -63,3 +81,98 @@ FUZZ_TARGET(rbf, .init = initialize_rbf)
         (void)IsRBFOptIn(tx, pool);
     }
 }
+
+void CheckDiagramConcave(std::vector<FeeFrac>& diagram)
+{
+    // Diagrams are in monotonically-decreasing feerate order.
+    FeeFrac last_chunk = diagram.front();
+    for (size_t i = 1; i<diagram.size(); ++i) {
+        FeeFrac next_chunk = diagram[i] - diagram[i-1];
+        assert(next_chunk <= last_chunk);
+        last_chunk = next_chunk;
+    }
+}
+
+FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    SetMockTime(ConsumeTime(fuzzed_data_provider));
+
+    std::optional<CMutableTransaction> child = ConsumeDeserializable<CMutableTransaction>(fuzzed_data_provider, TX_WITH_WITNESS);
+    if (!child) return;
+
+    CTxMemPool pool{MemPoolOptionsForTest(g_setup->m_node)};
+
+    // Add a bunch of parent-child pairs to the mempool, and remember them.
+    std::vector<CTransaction> mempool_txs;
+    size_t iter{0};
+
+    LOCK2(cs_main, pool.cs);
+
+    LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), NUM_ITERS)
+    {
+        // Make sure txns only have one input, and that a unique input is given to avoid circular references
+        std::optional<CMutableTransaction> parent = ConsumeDeserializable<CMutableTransaction>(fuzzed_data_provider, TX_WITH_WITNESS);
+        if (!parent) {
+            continue;
+        }
+        assert(iter <= g_outpoints.size());
+        parent->vin.resize(1);
+        parent->vin[0].prevout = g_outpoints[iter++];
+
+        mempool_txs.emplace_back(*parent);
+        pool.addUnchecked(ConsumeTxMemPoolEntry(fuzzed_data_provider, mempool_txs.back()));
+        if (fuzzed_data_provider.ConsumeBool() && !child->vin.empty()) {
+            child->vin[0].prevout = COutPoint{mempool_txs.back().GetHash(), 0};
+        }
+        mempool_txs.emplace_back(*child);
+        pool.addUnchecked(ConsumeTxMemPoolEntry(fuzzed_data_provider, mempool_txs.back()));
+    }
+
+    // Pick some transactions at random to be the direct conflicts
+    CTxMemPool::setEntries direct_conflicts;
+    for (auto& tx : mempool_txs) {
+        if (fuzzed_data_provider.ConsumeBool()) {
+            direct_conflicts.insert(*pool.GetIter(tx.GetHash()));
+        }
+    }
+
+    // Calculate all conflicts:
+    CTxMemPool::setEntries all_conflicts;
+    for (auto& txiter : direct_conflicts) {
+        pool.CalculateDescendants(txiter, all_conflicts);
+    }
+
+    // Calculate the feerate diagrams for a replacement.
+    CAmount replacement_fees = ConsumeMoney(fuzzed_data_provider);
+    int64_t replacement_vsize = fuzzed_data_provider.ConsumeIntegralInRange<int64_t>(1, 1000000);
+    auto calc_results{pool.CalculateFeerateDiagramsForRBF(replacement_fees, replacement_vsize, direct_conflicts, all_conflicts)};
+
+    if (calc_results.has_value()) {
+        // Sanity checks on the diagrams.
+
+        // Diagrams start at 0.
+        assert(calc_results->first.front().size == 0);
+        assert(calc_results->first.front().fee == 0);
+        assert(calc_results->second.front().size == 0);
+        assert(calc_results->second.front().fee == 0);
+
+        CheckDiagramConcave(calc_results->first);
+        CheckDiagramConcave(calc_results->second);
+
+        CAmount replaced_fee{0};
+        int64_t replaced_size{0};
+        for (auto txiter : all_conflicts) {
+            replaced_fee += txiter->GetModifiedFee();
+            replaced_size += txiter->GetTxSize();
+        }
+        // The total fee of the new diagram should be the total fee of the old
+        // diagram - replaced_fee + replacement_fees
+        assert(calc_results->first.back().fee - replaced_fee + replacement_fees == calc_results->second.back().fee);
+        assert(calc_results->first.back().size - replaced_size + replacement_vsize == calc_results->second.back().size);
+    }
+
+    // If internals report error, wrapper should too
+    auto err_tuple{ImprovesFeerateDiagram(pool, direct_conflicts, all_conflicts, replacement_fees, replacement_vsize)};
+    if (!calc_results.has_value()) assert(err_tuple.has_value());
+}