tx fees, policy: read stale fee estimates with a regtest-only option

If -acceptstalefeeestimates option is passed stale fee estimates can now
be read when operating in regtest environments.

Additionally, this commit updates all declarations of the CBlockPolicyEstimator
class to include a the second constructor variable.

Github-Pull: #27622
Rebased-From: cf219f29f3c5b41070eaab9a549a476f01990f3a

6 files changed, 16 insertions, 7 deletions

diff --git a/src/init.cpp b/src/init.cpp
index e9644e9c35..aa8d4b937c 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -79,6 +79,7 @@
 #include <util/system.h>
 #include <util/thread.h>
 #include <util/threadnames.h>
+#include <util/time.h>
 #include <util/translation.h>
 #include <validation.h>
 #include <validationinterface.h>
@@ -579,6 +580,7 @@ void SetupServerArgs(ArgsManager& argsman)
     argsman.AddArg("-acceptnonstdtxn", strprintf("Relay and mine \"non-standard\" transactions (%sdefault: %u)", "testnet/regtest only; ", !testnetChainParams->RequireStandard()), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::NODE_RELAY);
     argsman.AddArg("-incrementalrelayfee=<amt>", strprintf("Fee rate (in %s/kvB) used to define cost of relay, used for mempool limiting and replacement policy. (default: %s)", CURRENCY_UNIT, FormatMoney(DEFAULT_INCREMENTAL_RELAY_FEE)), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::NODE_RELAY);
     argsman.AddArg("-dustrelayfee=<amt>", strprintf("Fee rate (in %s/kvB) used to define dust, the value of an output such that it will cost more than its value in fees at this fee rate to spend it. (default: %s)", CURRENCY_UNIT, FormatMoney(DUST_RELAY_TX_FEE)), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::NODE_RELAY);
+    argsman.AddArg("-acceptstalefeeestimates", strprintf("Read fee estimates even if they are stale (%sdefault: %u) fee estimates are considered stale if they are %s hours old", "regtest only; ", DEFAULT_ACCEPT_STALE_FEE_ESTIMATES, Ticks<std::chrono::hours>(MAX_FILE_AGE)), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-bytespersigop", strprintf("Equivalent bytes per sigop in transactions for relay and mining (default: %u)", DEFAULT_BYTES_PER_SIGOP), ArgsManager::ALLOW_ANY, OptionsCategory::NODE_RELAY);
     argsman.AddArg("-datacarrier", strprintf("Relay and mine data carrier transactions (default: %u)", DEFAULT_ACCEPT_DATACARRIER), ArgsManager::ALLOW_ANY, OptionsCategory::NODE_RELAY);
     argsman.AddArg("-datacarriersize", strprintf("Maximum size of data in data carrier transactions we relay and mine (default: %u)", MAX_OP_RETURN_RELAY), ArgsManager::ALLOW_ANY, OptionsCategory::NODE_RELAY);
@@ -1252,7 +1254,11 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     // Don't initialize fee estimation with old data if we don't relay transactions,
     // as they would never get updated.
     if (!ignores_incoming_txs) {
-        node.fee_estimator = std::make_unique<CBlockPolicyEstimator>(FeeestPath(args));
+        bool read_stale_estimates = args.GetBoolArg("-acceptstalefeeestimates", DEFAULT_ACCEPT_STALE_FEE_ESTIMATES);
+        if (read_stale_estimates && (chainparams.NetworkIDString() != CBaseChainParams::REGTEST)) {
+            return InitError(strprintf(_("acceptstalefeeestimates is not supported on %s chain."), chainparams.NetworkIDString()));
+        }
+        node.fee_estimator = std::make_unique<CBlockPolicyEstimator>(FeeestPath(args), read_stale_estimates);
 
         // Flush estimates to disk periodically
         CBlockPolicyEstimator* fee_estimator = node.fee_estimator.get();
diff --git a/src/policy/fees.cpp b/src/policy/fees.cpp
index d88ae3ae0d..ee9d4222d3 100644
--- a/src/policy/fees.cpp
+++ b/src/policy/fees.cpp
@@ -528,7 +528,7 @@ bool CBlockPolicyEstimator::_removeTx(const uint256& hash, bool inBlock)
     }
 }
 
-CBlockPolicyEstimator::CBlockPolicyEstimator(const fs::path& estimation_filepath)
+CBlockPolicyEstimator::CBlockPolicyEstimator(const fs::path& estimation_filepath, const bool read_stale_estimates)
     : m_estimation_filepath{estimation_filepath}
 {
     static_assert(MIN_BUCKET_FEERATE > 0, "Min feerate must be nonzero");
@@ -556,7 +556,7 @@ CBlockPolicyEstimator::CBlockPolicyEstimator(const fs::path& estimation_filepath
 
     std::chrono::hours file_age = GetFeeEstimatorFileAge();
     // fee estimate file must not be too old to avoid wrong fee estimates.
-    if (file_age > MAX_FILE_AGE) {
+    if (file_age > MAX_FILE_AGE && !read_stale_estimates) {
         LogPrintf("Fee estimation file %s too old (age=%lld > %lld hours) and will not be used to avoid serving stale estimates.\n", fs::PathToString(m_estimation_filepath), Ticks<std::chrono::hours>(file_age), Ticks<std::chrono::hours>(MAX_FILE_AGE));
         return;
     }
diff --git a/src/policy/fees.h b/src/policy/fees.h
index a348ba05d8..52761f03ca 100644
--- a/src/policy/fees.h
+++ b/src/policy/fees.h
@@ -30,6 +30,9 @@ static constexpr std::chrono::hours FEE_FLUSH_INTERVAL{1};
  */
 static constexpr std::chrono::hours MAX_FILE_AGE{60};
 
+// Whether we allow importing a fee_estimates file older than MAX_FILE_AGE.
+static constexpr bool DEFAULT_ACCEPT_STALE_FEE_ESTIMATES{false};
+
 class AutoFile;
 class CTxMemPoolEntry;
 class TxConfirmStats;
@@ -193,7 +196,7 @@ private:
     const fs::path m_estimation_filepath;
 public:
     /** Create new BlockPolicyEstimator and initialize stats tracking classes with default values */
-    CBlockPolicyEstimator(const fs::path& estimation_filepath);
+    CBlockPolicyEstimator(const fs::path& estimation_filepath, const bool read_stale_estimates);
     ~CBlockPolicyEstimator();
 
     /** Process all the transactions that have been included in a block */
diff --git a/src/test/fuzz/policy_estimator.cpp b/src/test/fuzz/policy_estimator.cpp
index 116fbd9015..aa3cfe81df 100644
--- a/src/test/fuzz/policy_estimator.cpp
+++ b/src/test/fuzz/policy_estimator.cpp
@@ -31,7 +31,7 @@ void initialize_policy_estimator()
 FUZZ_TARGET_INIT(policy_estimator, initialize_policy_estimator)
 {
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
-    CBlockPolicyEstimator block_policy_estimator{FeeestPath(*g_setup->m_node.args)};
+    CBlockPolicyEstimator block_policy_estimator{FeeestPath(*g_setup->m_node.args), DEFAULT_ACCEPT_STALE_FEE_ESTIMATES};
     LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), 10000) {
         CallOneOf(
             fuzzed_data_provider,
diff --git a/src/test/fuzz/policy_estimator_io.cpp b/src/test/fuzz/policy_estimator_io.cpp
index 7c3289cd26..3df40197d8 100644
--- a/src/test/fuzz/policy_estimator_io.cpp
+++ b/src/test/fuzz/policy_estimator_io.cpp
@@ -28,7 +28,7 @@ FUZZ_TARGET_INIT(policy_estimator_io, initialize_policy_estimator_io)
     FuzzedAutoFileProvider fuzzed_auto_file_provider = ConsumeAutoFile(fuzzed_data_provider);
     AutoFile fuzzed_auto_file{fuzzed_auto_file_provider.open()};
     // Re-using block_policy_estimator across runs to avoid costly creation of CBlockPolicyEstimator object.
-    static CBlockPolicyEstimator block_policy_estimator{FeeestPath(*g_setup->m_node.args)};
+    static CBlockPolicyEstimator block_policy_estimator{FeeestPath(*g_setup->m_node.args), DEFAULT_ACCEPT_STALE_FEE_ESTIMATES};
     if (block_policy_estimator.Read(fuzzed_auto_file)) {
         block_policy_estimator.Write(fuzzed_auto_file);
     }
diff --git a/src/test/util/setup_common.cpp b/src/test/util/setup_common.cpp
index 58593c9d5b..e9cf177666 100644
--- a/src/test/util/setup_common.cpp
+++ b/src/test/util/setup_common.cpp
@@ -173,7 +173,7 @@ ChainTestingSetup::ChainTestingSetup(const std::string& chainName, const std::ve
     m_node.scheduler->m_service_thread = std::thread(util::TraceThread, "scheduler", [&] { m_node.scheduler->serviceQueue(); });
     GetMainSignals().RegisterBackgroundSignalScheduler(*m_node.scheduler);
 
-    m_node.fee_estimator = std::make_unique<CBlockPolicyEstimator>(FeeestPath(*m_node.args));
+    m_node.fee_estimator = std::make_unique<CBlockPolicyEstimator>(FeeestPath(*m_node.args), DEFAULT_ACCEPT_STALE_FEE_ESTIMATES);
     m_node.mempool = std::make_unique<CTxMemPool>(MemPoolOptionsForTest(m_node));
 
     m_cache_sizes = CalculateCacheSizes(m_args);