[fees]: add last block forecaster

src/Makefile.am

@@ -254,6 +254,7 @@ BITCOIN_CORE_H = \
   policy/forecasters/block.h \
   policy/forecasters/mempool.h \
   policy/forecasters/mempool_last_10_min.h \
+  policy/forecasters/last_block.h \
   policy/policy.h \
   policy/rbf.h \
   policy/settings.h \
@@ -461,6 +462,7 @@ libbitcoin_node_a_SOURCES = \
   policy/forecasters/block.cpp \
   policy/forecasters/mempool.cpp \
   policy/forecasters/mempool_last_10_min.cpp \
+  policy/forecasters/last_block.cpp \
   policy/packages.cpp \
   policy/rbf.cpp \
   policy/settings.cpp \

src/init.cpp

@@ -59,6 +59,7 @@
 #include <policy/fees.h>
 #include <policy/fees_args.h>
 #include <policy/forecasters/block.h>
+#include <policy/forecasters/last_block.h>
 #include <policy/forecasters/mempool.h>
 #include <policy/forecasters/mempool_last_10_min.h>
 #include <policy/policy.h>
@@ -1647,8 +1648,11 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     node.fee_estimator->RegisterForecaster(std::make_unique<MemPoolForecaster>(node.mempool.get(), &(chainman.ActiveChainstate())));
     node.fee_estimator->RegisterForecaster(std::make_unique<MemPoolLast10MinForecaster>(node.mempool.get(), &(chainman.ActiveChainstate())));
     auto block_estimator = std::make_shared<BlockForecaster>();
+    auto last_block_estimator = std::make_shared<LastBlockForecaster>();
     validation_signals.RegisterValidationInterface(block_estimator.get());
+    validation_signals.RegisterValidationInterface(last_block_estimator.get());
     node.fee_estimator->RegisterForecaster(block_estimator);
+    node.fee_estimator->RegisterForecaster(last_block_estimator);
     FeeEstimator* fee_estimator = node.fee_estimator.get();
     node.scheduler->scheduleEvery([fee_estimator] { fee_estimator->GetAllEstimates(/*targetBlocks=*/1); }, FEE_ESTIMATE_INTERVAL);
     assert(!node.peerman);

src/policy/forecasters/last_block.cpp

@@ -0,0 +1,56 @@
+// Copyright (c) 2024 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <kernel/mempool_entry.h>
+#include <logging.h>
+#include <policy/fee_estimator.h>
+#include <policy/forecasters/last_block.h>
+#include <util/trace.h>
+
+
+void LastBlockForecaster::MempoolTransactionsRemovedForBlock(const std::vector<RemovedMempoolTransactionInfo>& txs_removed_for_block, unsigned int nBlockHeight)
+{
+    chain_tip_height = nBlockHeight;
+    const std::vector<std::tuple<CFeeRate, uint64_t>> size_per_feerate = LinearizeTransactions(txs_removed_for_block).size_per_feerate;
+    BlockPercentiles percentiles = CalculateBlockPercentiles(size_per_feerate);
+    if (percentiles.p75 != CFeeRate(0)) {
+        blocks_percentile = percentiles;
+    }
+}
+
+ForecastResult LastBlockForecaster::EstimateFee(unsigned int targetBlocks)
+{
+    ForecastResult::ForecastOptions forecast_options;
+    forecast_options.m_forecaster = LAST_BLOCK_FORECAST_NAME_STR;
+    forecast_options.m_block_height = chain_tip_height;
+    if (targetBlocks <= 0) {
+        return ForecastResult(forecast_options, strprintf("%s: Confirmation target must be greater than zero", LAST_BLOCK_FORECAST_NAME_STR));
+    }
+
+    if (targetBlocks > LAST_BLOCK_FORECAST_MAX_TARGET) {
+        return ForecastResult(forecast_options, strprintf("%s: Confirmation target %u is above the maximum limit of %u",
+                                                          LAST_BLOCK_FORECAST_NAME_STR, targetBlocks, LAST_BLOCK_FORECAST_MAX_TARGET));
+    }
+
+    if (blocks_percentile.empty()) {
+        return ForecastResult(forecast_options, strprintf("%s: Insufficient block data to perform an estimate", LAST_BLOCK_FORECAST_NAME_STR));
+    }
+
+
+    LogPrint(BCLog::ESTIMATEFEE, "FeeEst: %s: Block height %s, 75th percentile fee rate %s %s/kvB, 50th percentile fee rate %s %s/kvB, 25th percentile fee rate %s %s/kvB, 5th percentile fee rate %s %s/kvB\n",
+             LAST_BLOCK_FORECAST_NAME_STR, chain_tip_height, blocks_percentile.p75.GetFeePerK(), CURRENCY_ATOM, blocks_percentile.p50.GetFeePerK(), CURRENCY_ATOM, blocks_percentile.p25.GetFeePerK(), CURRENCY_ATOM, blocks_percentile.p5.GetFeePerK(), CURRENCY_ATOM);
+
+    TRACE7(feerate_forecast, forecast_generated,
+           targetBlocks,
+           LAST_BLOCK_FORECAST_NAME_STR.c_str(),
+           chain_tip_height,
+           blocks_percentile.p5.GetFeePerK(),
+           blocks_percentile.p25.GetFeePerK(),
+           blocks_percentile.p50.GetFeePerK(),
+           blocks_percentile.p75.GetFeePerK());
+
+    forecast_options.m_l_priority_estimate = blocks_percentile.p25;
+    forecast_options.m_h_priority_estimate = blocks_percentile.p50;
+    return ForecastResult(forecast_options, std::nullopt);
+}

src/policy/forecasters/last_block.h

@@ -0,0 +1,49 @@
+// Copyright (c) 2024 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_POLICY_FORECASTERS_LAST_BLOCK_H
+#define BITCOIN_POLICY_FORECASTERS_LAST_BLOCK_H
+
+#include <policy/fees_util.h>
+#include <policy/forecaster.h>
+#include <validationinterface.h>
+
+#include <queue>
+
+
+struct RemovedMempoolTransactionInfo;
+class Forecaster;
+class CValidationInterface;
+struct ForecastResult;
+
+const std::string LAST_BLOCK_FORECAST_NAME_STR{"Last Block Forecast"};
+const unsigned int LAST_BLOCK_FORECAST_MAX_TARGET{2};
+
+/** \class LastBlockForecaster
+ * LastBlockForecaster fee rate forecaster estimates the fee rate that a transaction will pay
+ * to be included in a block as soon as possible.
+ * LastBlockForecaster uses the mining score of the transactions that were confirmed in
+ * the last block that the node mempool sees.
+ * LastBlockForecaster calculates the percentiles mining score
+ * It returns the 25th and 50th percentiles as the fee rate estimate.
+ */
+class LastBlockForecaster : public CValidationInterface, public Forecaster
+{
+private:
+    BlockPercentiles blocks_percentile;
+    unsigned int chain_tip_height;
+
+protected:
+    void MempoolTransactionsRemovedForBlock(const std::vector<RemovedMempoolTransactionInfo>& txs_removed_for_block, unsigned int nBlockHeight) override;
+
+public:
+    LastBlockForecaster(){};
+
+    ForecastResult EstimateFee(unsigned int targetBlocks) override;
+    unsigned int MaxTarget() override
+    {
+        return LAST_BLOCK_FORECAST_MAX_TARGET;
+    }
+};
+#endif // BITCOIN_POLICY_FORECASTERS_LAST_BLOCK_H