miner: add package feerate vector to CBlockTemplate

- The package feerates are ordered by the sequence in which
  packages are selected for inclusion in the block template.

- The commit also tests this new behaviour.

Co-authored-by: willcl-ark <will@256k1.dev>

src/node/miner.cpp

@@ -421,6 +421,7 @@ void BlockAssembler::addPackageTxs(int& nPackagesSelected, int& nDescendantsUpda
         }
 
         ++nPackagesSelected;
+        pblocktemplate->m_package_feerates.emplace_back(packageFees, static_cast<int32_t>(packageSize));
 
         // Update transactions that depend on each of these
         nDescendantsUpdated += UpdatePackagesForAdded(mempool, ancestors, mapModifiedTx);

src/node/miner.h

@@ -10,6 +10,7 @@
 #include <policy/policy.h>
 #include <primitives/block.h>
 #include <txmempool.h>
+#include <util/feefrac.h>
 
 #include <memory>
 #include <optional>
@@ -39,6 +40,9 @@ struct CBlockTemplate
     std::vector<CAmount> vTxFees;
     std::vector<int64_t> vTxSigOpsCost;
     std::vector<unsigned char> vchCoinbaseCommitment;
+    /* A vector of package fee rates, ordered by the sequence in which
+     * packages are selected for inclusion in the block template.*/
+    std::vector<FeeFrac> m_package_feerates;
 };
 
 // Container for tracking updates to ancestor feerate as we include (parent)

src/test/miner_tests.cpp

@@ -16,6 +16,7 @@
 #include <txmempool.h>
 #include <uint256.h>
 #include <util/check.h>
+#include <util/feefrac.h>
 #include <util/strencodings.h>
 #include <util/time.h>
 #include <util/translation.h>
@@ -25,6 +26,7 @@
 #include <test/util/setup_common.h>
 
 #include <memory>
+#include <vector>
 
 #include <boost/test/unit_test.hpp>
 
@@ -123,19 +125,22 @@ void MinerTestingSetup::TestPackageSelection(const CScript& scriptPubKey, const
     tx.vout[0].nValue = 5000000000LL - 1000;
     // This tx has a low fee: 1000 satoshis
     Txid hashParentTx = tx.GetHash(); // save this txid for later use
-    AddToMempool(tx_mempool, entry.Fee(1000).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx));
+    const auto parent_tx{entry.Fee(1000).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx)};
+    AddToMempool(tx_mempool, parent_tx);
 
     // This tx has a medium fee: 10000 satoshis
     tx.vin[0].prevout.hash = txFirst[1]->GetHash();
     tx.vout[0].nValue = 5000000000LL - 10000;
     Txid hashMediumFeeTx = tx.GetHash();
-    AddToMempool(tx_mempool, entry.Fee(10000).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx));
+    const auto medium_fee_tx{entry.Fee(10000).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx)};
+    AddToMempool(tx_mempool, medium_fee_tx);
 
     // This tx has a high fee, but depends on the first transaction
     tx.vin[0].prevout.hash = hashParentTx;
     tx.vout[0].nValue = 5000000000LL - 1000 - 50000; // 50k satoshi fee
     Txid hashHighFeeTx = tx.GetHash();
-    AddToMempool(tx_mempool, entry.Fee(50000).Time(Now<NodeSeconds>()).SpendsCoinbase(false).FromTx(tx));
+    const auto high_fee_tx{entry.Fee(50000).Time(Now<NodeSeconds>()).SpendsCoinbase(false).FromTx(tx)};
+    AddToMempool(tx_mempool, high_fee_tx);
 
     std::unique_ptr<BlockTemplate> block_template = mining->createNewBlock(options);
     BOOST_REQUIRE(block_template);
@@ -145,6 +150,21 @@ void MinerTestingSetup::TestPackageSelection(const CScript& scriptPubKey, const
     BOOST_CHECK(block.vtx[2]->GetHash() == hashHighFeeTx);
     BOOST_CHECK(block.vtx[3]->GetHash() == hashMediumFeeTx);
 
+    // Test the inclusion of package feerates in the block template and ensure they are sequential.
+    const auto block_package_feerates = BlockAssembler{m_node.chainman->ActiveChainstate(), &tx_mempool, options}.CreateNewBlock()->m_package_feerates;
+    BOOST_CHECK(block_package_feerates.size() == 2);
+
+    // parent_tx and high_fee_tx are added to the block as a package.
+    const auto combined_txs_fee = parent_tx.GetFee() + high_fee_tx.GetFee();
+    const auto combined_txs_size = parent_tx.GetTxSize() + high_fee_tx.GetTxSize();
+    FeeFrac package_feefrac{combined_txs_fee, combined_txs_size};
+    // The package should be added first.
+    BOOST_CHECK(block_package_feerates[0] == package_feefrac);
+
+    // The medium_fee_tx should be added next.
+    FeeFrac medium_tx_feefrac{medium_fee_tx.GetFee(), medium_fee_tx.GetTxSize()};
+    BOOST_CHECK(block_package_feerates[1] == medium_tx_feefrac);
+
     // Test that a package below the block min tx fee doesn't get included
     tx.vin[0].prevout.hash = hashHighFeeTx;
     tx.vout[0].nValue = 5000000000LL - 1000 - 50000; // 0 fee