test: ensure old fee_estimate.dat not read on restart and flushed

This commit adds tests to ensure that old fee_estimates.dat files
are not read and that fee_estimates are periodically flushed to the
fee_estimates.dat file.

Additionaly it tests the -regtestonly option -acceptstalefeeestimates.

Github-Pull: #27622
Rebased-From: d2b39e0

test/functional/feature_fee_estimation.py

@@ -7,6 +7,7 @@
 from decimal import Decimal
 import os
 import random
+import time
 
 from test_framework.messages import (
     COIN,
@@ -21,6 +22,8 @@
 )
 from test_framework.wallet import MiniWallet
 
+MAX_FILE_AGE = 60
+SECONDS_PER_HOUR = 60 * 60
 
 def small_txpuzzle_randfee(
     wallet, from_node, conflist, unconflist, amount, min_fee, fee_increment
@@ -273,6 +276,95 @@ def sanity_check_rbf_estimates(self, utxos):
         est_feerate = node.estimatesmartfee(2)["feerate"]
         assert_equal(est_feerate, high_feerate_kvb)
 
+    def test_old_fee_estimate_file(self):
+        # Get the initial fee rate while node is running
+        fee_rate = self.nodes[0].estimatesmartfee(1)["feerate"]
+
+        # Restart node to ensure fee_estimate.dat file is read
+        self.restart_node(0)
+        assert_equal(self.nodes[0].estimatesmartfee(1)["feerate"], fee_rate)
+
+        fee_dat = self.nodes[0].chain_path / "fee_estimates.dat"
+
+        # Stop the node and backdate the fee_estimates.dat file more than MAX_FILE_AGE
+        self.stop_node(0)
+        last_modified_time = time.time() - (MAX_FILE_AGE + 1) * SECONDS_PER_HOUR
+        os.utime(fee_dat, (last_modified_time, last_modified_time))
+
+        # Start node and ensure the fee_estimates.dat file was not read
+        self.start_node(0)
+        assert_equal(self.nodes[0].estimatesmartfee(1)["errors"], ["Insufficient data or no feerate found"])
+
+
+    def test_estimate_dat_is_flushed_periodically(self):
+        fee_dat = self.nodes[0].chain_path / "fee_estimates.dat"
+        os.remove(fee_dat) if os.path.exists(fee_dat) else None
+
+        # Verify that fee_estimates.dat does not exist
+        assert_equal(os.path.isfile(fee_dat), False)
+
+        # Verify if the string "Flushed fee estimates to fee_estimates.dat." is present in the debug log file.
+        # If present, it indicates that fee estimates have been successfully flushed to disk.
+        with self.nodes[0].assert_debug_log(expected_msgs=["Flushed fee estimates to fee_estimates.dat."], timeout=1):
+            # Mock the scheduler for an hour to flush fee estimates to fee_estimates.dat
+            self.nodes[0].mockscheduler(SECONDS_PER_HOUR)
+
+        # Verify that fee estimates were flushed and fee_estimates.dat file is created
+        assert_equal(os.path.isfile(fee_dat), True)
+
+        # Verify that the estimates remain the same if there are no blocks in the flush interval
+        block_hash_before = self.nodes[0].getbestblockhash()
+        fee_dat_initial_content = open(fee_dat, "rb").read()
+        with self.nodes[0].assert_debug_log(expected_msgs=["Flushed fee estimates to fee_estimates.dat."], timeout=1):
+            # Mock the scheduler for an hour to flush fee estimates to fee_estimates.dat
+            self.nodes[0].mockscheduler(SECONDS_PER_HOUR)
+
+        # Verify that there were no blocks in between the flush interval
+        assert_equal(block_hash_before, self.nodes[0].getbestblockhash())
+
+        fee_dat_current_content = open(fee_dat, "rb").read()
+        assert_equal(fee_dat_current_content, fee_dat_initial_content)
+
+        # Verify that the estimates remain the same after shutdown with no blocks before shutdown
+        self.restart_node(0)
+        fee_dat_current_content = open(fee_dat, "rb").read()
+        assert_equal(fee_dat_current_content, fee_dat_initial_content)
+
+        # Verify that the estimates are not the same if new blocks were produced in the flush interval
+        with self.nodes[0].assert_debug_log(expected_msgs=["Flushed fee estimates to fee_estimates.dat."], timeout=1):
+            # Mock the scheduler for an hour to flush fee estimates to fee_estimates.dat
+            self.generate(self.nodes[0], 5, sync_fun=self.no_op)
+            self.nodes[0].mockscheduler(SECONDS_PER_HOUR)
+
+        fee_dat_current_content = open(fee_dat, "rb").read()
+        assert fee_dat_current_content != fee_dat_initial_content
+
+        fee_dat_initial_content = fee_dat_current_content
+
+        # Generate blocks before shutdown and verify that the fee estimates are not the same
+        self.generate(self.nodes[0], 5, sync_fun=self.no_op)
+        self.restart_node(0)
+        fee_dat_current_content = open(fee_dat, "rb").read()
+        assert fee_dat_current_content != fee_dat_initial_content
+
+
+    def test_acceptstalefeeestimates_option(self):
+        # Get the initial fee rate while node is running
+        fee_rate = self.nodes[0].estimatesmartfee(1)["feerate"]
+
+        self.stop_node(0)
+
+        fee_dat = self.nodes[0].chain_path / "fee_estimates.dat"
+
+        # Stop the node and backdate the fee_estimates.dat file more than MAX_FILE_AGE
+        last_modified_time = time.time() - (MAX_FILE_AGE + 1) * SECONDS_PER_HOUR
+        os.utime(fee_dat, (last_modified_time, last_modified_time))
+
+        # Restart node with -acceptstalefeeestimates option to ensure fee_estimate.dat file is read
+        self.start_node(0,extra_args=["-acceptstalefeeestimates"])
+        assert_equal(self.nodes[0].estimatesmartfee(1)["feerate"], fee_rate)
+
+
     def run_test(self):
         self.log.info("This test is time consuming, please be patient")
         self.log.info("Splitting inputs so we can generate tx's")
@@ -296,12 +388,21 @@ def run_test(self):
         self.log.info("Testing estimates with single transactions.")
         self.sanity_check_estimates_range()
 
+        self.log.info("Test fee_estimates.dat is flushed periodically")
+        self.test_estimate_dat_is_flushed_periodically()
+
         # check that the effective feerate is greater than or equal to the mempoolminfee even for high mempoolminfee
         self.log.info(
             "Test fee rate estimation after restarting node with high MempoolMinFee"
         )
         self.test_feerate_mempoolminfee()
 
+        self.log.info("Test acceptstalefeeestimates option")
+        self.test_acceptstalefeeestimates_option()
+
+        self.log.info("Test reading old fee_estimates.dat")
+        self.test_old_fee_estimate_file()
+
         self.log.info("Restarting node with fresh estimation")
         self.stop_node(0)
         fee_dat = os.path.join(self.nodes[0].datadir, self.chain, "fee_estimates.dat")