Merge #21062: refactor: return MempoolAcceptResult from ATMP

53e716ea119658c28935fee24eb50090907c500e [refactor] improve style for touched code (gzhao408)
174cb5330af4b09f3a66974d3bae783ea43b190e [refactor] const ATMPArgs and non-const Workspace (gzhao408)
f82baf0762f60c2ca5ffc339b095f9271d7c2f33 [refactor] return MempoolAcceptResult (gzhao408)
9db10a55061e09021ff8ea1d6637d99f7959035f [refactor] clean up logic in testmempoolaccept (gzhao408)

Pull request description:

  This is the first 4 commits of #20833, and does refactoring only. It should be relatively simple to review, and offers a few nice things:
  - It makes accessing values that don't make sense (e.g. fee) when the tx is invalid an error.
  - Returning `MempoolAcceptResult` from ATMP makes the interface cleaner. The caller can get a const instead of passing in a mutable "out" param.
  - We don't have to be iterating through a bunch of lists for package validation, we can just return a `std::vector<MempoolAcceptResult>`.
  - We don't have to refactor all ATMP call sites again if/when we want to return more stuff from it.

ACKs for top commit:
  MarcoFalke:
    ACK 53e716ea119658c28935fee24eb50090907c500e 💿
  jnewbery:
    Code review ACK 53e716ea119658c28935fee24eb50090907c500e
  ariard:
    Code Review ACK 53e716e, I did tweak a bit the touched paths to see if we had good test coverage. Didn't find holes.

Tree-SHA512: fa6ec324a08ad9e6e55948615cda324cba176255708bf0a0a0f37cedb7a75311aa334ac6f223be7d8df3c7379502b1081102b9589f9a9afa1713ad3d9ab3c24f

1 files changed, 42 insertions, 55 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index 8f7d36bfd3..9938b62640 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -380,10 +380,8 @@ static void UpdateMempoolForReorg(CTxMemPool& mempool, DisconnectedBlockTransact
     auto it = disconnectpool.queuedTx.get<insertion_order>().rbegin();
     while (it != disconnectpool.queuedTx.get<insertion_order>().rend()) {
         // ignore validation errors in resurrected transactions
-        TxValidationState stateDummy;
         if (!fAddToMempool || (*it)->IsCoinBase() ||
-            !AcceptToMemoryPool(mempool, stateDummy, *it,
-                                nullptr /* plTxnReplaced */, true /* bypass_limits */)) {
+            AcceptToMemoryPool(mempool, *it, true /* bypass_limits */).m_result_type != MempoolAcceptResult::ResultType::VALID) {
             // If the transaction doesn't make it in to the mempool, remove any
             // transactions that depend on it (which would now be orphans).
             mempool.removeRecursive(**it, MemPoolRemovalReason::REORG);
@@ -463,9 +461,7 @@ public:
     // around easier.
     struct ATMPArgs {
         const CChainParams& m_chainparams;
-        TxValidationState &m_state;
         const int64_t m_accept_time;
-        std::list<CTransactionRef>* m_replaced_transactions;
         const bool m_bypass_limits;
         /*
          * Return any outpoints which were not previously present in the coins
@@ -476,11 +472,10 @@ public:
          */
         std::vector<COutPoint>& m_coins_to_uncache;
         const bool m_test_accept;
-        CAmount* m_fee_out;
     };
 
     // Single transaction acceptance
-    bool AcceptSingleTransaction(const CTransactionRef& ptx, ATMPArgs& args) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    MempoolAcceptResult AcceptSingleTransaction(const CTransactionRef& ptx, ATMPArgs& args) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
 private:
     // All the intermediate state that gets passed between the various levels
@@ -491,14 +486,17 @@ private:
         CTxMemPool::setEntries m_all_conflicting;
         CTxMemPool::setEntries m_ancestors;
         std::unique_ptr<CTxMemPoolEntry> m_entry;
+        std::list<CTransactionRef> m_replaced_transactions;
 
         bool m_replacement_transaction;
+        CAmount m_base_fees;
         CAmount m_modified_fees;
         CAmount m_conflicting_fees;
         size_t m_conflicting_size;
 
         const CTransactionRef& m_ptx;
         const uint256& m_hash;
+        TxValidationState m_state;
     };
 
     // Run the policy checks on a given transaction, excluding any script checks.
@@ -509,18 +507,18 @@ private:
 
     // Run the script checks using our policy flags. As this can be slow, we should
     // only invoke this on transactions that have otherwise passed policy checks.
-    bool PolicyScriptChecks(ATMPArgs& args, const Workspace& ws, PrecomputedTransactionData& txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
+    bool PolicyScriptChecks(const ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
 
     // Re-run the script checks, using consensus flags, and try to cache the
     // result in the scriptcache. This should be done after
     // PolicyScriptChecks(). This requires that all inputs either be in our
     // utxo set or in the mempool.
-    bool ConsensusScriptChecks(ATMPArgs& args, const Workspace& ws, PrecomputedTransactionData &txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
+    bool ConsensusScriptChecks(const ATMPArgs& args, Workspace& ws, PrecomputedTransactionData &txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
 
     // Try to add the transaction to the mempool, removing any conflicts first.
     // Returns true if the transaction is in the mempool after any size
     // limiting is performed, false otherwise.
-    bool Finalize(ATMPArgs& args, Workspace& ws) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
+    bool Finalize(const ATMPArgs& args, Workspace& ws) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
 
     // Compare a package's feerate against minimum allowed.
     bool CheckFeeRate(size_t package_size, CAmount package_fee, TxValidationState& state) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs)
@@ -558,12 +556,12 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
     const uint256& hash = ws.m_hash;
 
     // Copy/alias what we need out of args
-    TxValidationState &state = args.m_state;
     const int64_t nAcceptTime = args.m_accept_time;
     const bool bypass_limits = args.m_bypass_limits;
     std::vector<COutPoint>& coins_to_uncache = args.m_coins_to_uncache;
 
     // Alias what we need out of ws
+    TxValidationState& state = ws.m_state;
     std::set<uint256>& setConflicts = ws.m_conflicts;
     CTxMemPool::setEntries& allConflicting = ws.m_all_conflicting;
     CTxMemPool::setEntries& setAncestors = ws.m_ancestors;
@@ -683,16 +681,10 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
     if (!CheckSequenceLocks(m_pool, tx, STANDARD_LOCKTIME_VERIFY_FLAGS, &lp))
         return state.Invalid(TxValidationResult::TX_PREMATURE_SPEND, "non-BIP68-final");
 
-    CAmount nFees = 0;
-    if (!Consensus::CheckTxInputs(tx, state, m_view, g_chainman.m_blockman.GetSpendHeight(m_view), nFees)) {
+    if (!Consensus::CheckTxInputs(tx, state, m_view, g_chainman.m_blockman.GetSpendHeight(m_view), ws.m_base_fees)) {
         return false; // state filled in by CheckTxInputs
     }
 
-    // If fee_out is passed, return the fee to the caller
-    if (args.m_fee_out) {
-        *args.m_fee_out = nFees;
-    }
-
     // Check for non-standard pay-to-script-hash in inputs
     const auto& params = args.m_chainparams.GetConsensus();
     auto taproot_state = VersionBitsState(::ChainActive().Tip(), params, Consensus::DEPLOYMENT_TAPROOT, versionbitscache);
@@ -707,7 +699,7 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
     int64_t nSigOpsCost = GetTransactionSigOpCost(tx, m_view, STANDARD_SCRIPT_VERIFY_FLAGS);
 
     // nModifiedFees includes any fee deltas from PrioritiseTransaction
-    nModifiedFees = nFees;
+    nModifiedFees = ws.m_base_fees;
     m_pool.ApplyDelta(hash, nModifiedFees);
 
     // Keep track of transactions that spend a coinbase, which we re-scan
@@ -721,7 +713,7 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
         }
     }
 
-    entry.reset(new CTxMemPoolEntry(ptx, nFees, nAcceptTime, ::ChainActive().Height(),
+    entry.reset(new CTxMemPoolEntry(ptx, ws.m_base_fees, nAcceptTime, ::ChainActive().Height(),
             fSpendsCoinbase, nSigOpsCost, lp));
     unsigned int nSize = entry->GetTxSize();
 
@@ -925,11 +917,10 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
     return true;
 }
 
-bool MemPoolAccept::PolicyScriptChecks(ATMPArgs& args, const Workspace& ws, PrecomputedTransactionData& txdata)
+bool MemPoolAccept::PolicyScriptChecks(const ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata)
 {
     const CTransaction& tx = *ws.m_ptx;
-
-    TxValidationState &state = args.m_state;
+    TxValidationState& state = ws.m_state;
 
     constexpr unsigned int scriptVerifyFlags = STANDARD_SCRIPT_VERIFY_FLAGS;
 
@@ -952,12 +943,11 @@ bool MemPoolAccept::PolicyScriptChecks(ATMPArgs& args, const Workspace& ws, Prec
     return true;
 }
 
-bool MemPoolAccept::ConsensusScriptChecks(ATMPArgs& args, const Workspace& ws, PrecomputedTransactionData& txdata)
+bool MemPoolAccept::ConsensusScriptChecks(const ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata)
 {
     const CTransaction& tx = *ws.m_ptx;
     const uint256& hash = ws.m_hash;
-
-    TxValidationState &state = args.m_state;
+    TxValidationState& state = ws.m_state;
     const CChainParams& chainparams = args.m_chainparams;
 
     // Check again against the current block tip's script verification
@@ -984,11 +974,11 @@ bool MemPoolAccept::ConsensusScriptChecks(ATMPArgs& args, const Workspace& ws, P
     return true;
 }
 
-bool MemPoolAccept::Finalize(ATMPArgs& args, Workspace& ws)
+bool MemPoolAccept::Finalize(const ATMPArgs& args, Workspace& ws)
 {
     const CTransaction& tx = *ws.m_ptx;
     const uint256& hash = ws.m_hash;
-    TxValidationState &state = args.m_state;
+    TxValidationState& state = ws.m_state;
     const bool bypass_limits = args.m_bypass_limits;
 
     CTxMemPool::setEntries& allConflicting = ws.m_all_conflicting;
@@ -1007,8 +997,7 @@ bool MemPoolAccept::Finalize(ATMPArgs& args, Workspace& ws)
                 hash.ToString(),
                 FormatMoney(nModifiedFees - nConflictingFees),
                 (int)entry->GetTxSize() - (int)nConflictingSize);
-        if (args.m_replaced_transactions)
-            args.m_replaced_transactions->push_back(it->GetSharedTx());
+        ws.m_replaced_transactions.push_back(it->GetSharedTx());
     }
     m_pool.RemoveStaged(allConflicting, false, MemPoolRemovalReason::REPLACED);
 
@@ -1031,14 +1020,14 @@ bool MemPoolAccept::Finalize(ATMPArgs& args, Workspace& ws)
     return true;
 }
 
-bool MemPoolAccept::AcceptSingleTransaction(const CTransactionRef& ptx, ATMPArgs& args)
+MempoolAcceptResult MemPoolAccept::AcceptSingleTransaction(const CTransactionRef& ptx, ATMPArgs& args)
 {
     AssertLockHeld(cs_main);
     LOCK(m_pool.cs); // mempool "read lock" (held through GetMainSignals().TransactionAddedToMempool())
 
-    Workspace workspace(ptx);
+    Workspace ws(ptx);
 
-    if (!PreChecks(args, workspace)) return false;
+    if (!PreChecks(args, ws)) return MempoolAcceptResult(ws.m_state);
 
     // Only compute the precomputed transaction data if we need to verify
     // scripts (ie, other policy checks pass). We perform the inexpensive
@@ -1046,31 +1035,35 @@ bool MemPoolAccept::AcceptSingleTransaction(const CTransactionRef& ptx, ATMPArgs
     // checks pass, to mitigate CPU exhaustion denial-of-service attacks.
     PrecomputedTransactionData txdata;
 
-    if (!PolicyScriptChecks(args, workspace, txdata)) return false;
+    if (!PolicyScriptChecks(args, ws, txdata)) return MempoolAcceptResult(ws.m_state);
 
-    if (!ConsensusScriptChecks(args, workspace, txdata)) return false;
+    if (!ConsensusScriptChecks(args, ws, txdata)) return MempoolAcceptResult(ws.m_state);
 
     // Tx was accepted, but not added
-    if (args.m_test_accept) return true;
+    if (args.m_test_accept) {
+        return MempoolAcceptResult(std::move(ws.m_replaced_transactions), ws.m_base_fees);
+    }
 
-    if (!Finalize(args, workspace)) return false;
+    if (!Finalize(args, ws)) return MempoolAcceptResult(ws.m_state);
 
     GetMainSignals().TransactionAddedToMempool(ptx, m_pool.GetAndIncrementSequence());
 
-    return true;
+    return MempoolAcceptResult(std::move(ws.m_replaced_transactions), ws.m_base_fees);
 }
 
 } // anon namespace
 
 /** (try to) add transaction to memory pool with a specified acceptance time **/
-static bool AcceptToMemoryPoolWithTime(const CChainParams& chainparams, CTxMemPool& pool, TxValidationState &state, const CTransactionRef &tx,
-                        int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
-                        bool bypass_limits, bool test_accept, CAmount* fee_out=nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
+static MempoolAcceptResult AcceptToMemoryPoolWithTime(const CChainParams& chainparams, CTxMemPool& pool,
+                                                      const CTransactionRef &tx, int64_t nAcceptTime,
+                                                      bool bypass_limits, bool test_accept)
+                                                      EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     std::vector<COutPoint> coins_to_uncache;
-    MemPoolAccept::ATMPArgs args { chainparams, state, nAcceptTime, plTxnReplaced, bypass_limits, coins_to_uncache, test_accept, fee_out };
-    bool res = MemPoolAccept(pool).AcceptSingleTransaction(tx, args);
-    if (!res) {
+    MemPoolAccept::ATMPArgs args { chainparams, nAcceptTime, bypass_limits, coins_to_uncache, test_accept };
+
+    const MempoolAcceptResult result = MemPoolAccept(pool).AcceptSingleTransaction(tx, args);
+    if (result.m_result_type != MempoolAcceptResult::ResultType::VALID) {
         // Remove coins that were not present in the coins cache before calling ATMPW;
         // this is to prevent memory DoS in case we receive a large number of
         // invalid transactions that attempt to overrun the in-memory coins cache
@@ -1082,15 +1075,12 @@ static bool AcceptToMemoryPoolWithTime(const CChainParams& chainparams, CTxMemPo
     // After we've (potentially) uncached entries, ensure our coins cache is still within its size limits
     BlockValidationState state_dummy;
     ::ChainstateActive().FlushStateToDisk(chainparams, state_dummy, FlushStateMode::PERIODIC);
-    return res;
+    return result;
 }
 
-bool AcceptToMemoryPool(CTxMemPool& pool, TxValidationState &state, const CTransactionRef &tx,
-                        std::list<CTransactionRef>* plTxnReplaced,
-                        bool bypass_limits, bool test_accept, CAmount* fee_out)
+MempoolAcceptResult AcceptToMemoryPool(CTxMemPool& pool, const CTransactionRef &tx, bool bypass_limits, bool test_accept)
 {
-    const CChainParams& chainparams = Params();
-    return AcceptToMemoryPoolWithTime(chainparams, pool, state, tx, GetTime(), plTxnReplaced, bypass_limits, test_accept, fee_out);
+    return AcceptToMemoryPoolWithTime(Params(), pool, tx, GetTime(), bypass_limits, test_accept);
 }
 
 CTransactionRef GetTransaction(const CBlockIndex* const block_index, const CTxMemPool* const mempool, const uint256& hash, const Consensus::Params& consensusParams, uint256& hashBlock)
@@ -5029,13 +5019,10 @@ bool LoadMempool(CTxMemPool& pool)
             if (amountdelta) {
                 pool.PrioritiseTransaction(tx->GetHash(), amountdelta);
             }
-            TxValidationState state;
             if (nTime > nNow - nExpiryTimeout) {
                 LOCK(cs_main);
-                AcceptToMemoryPoolWithTime(chainparams, pool, state, tx, nTime,
-                                           nullptr /* plTxnReplaced */, false /* bypass_limits */,
-                                           false /* test_accept */);
-                if (state.IsValid()) {
+                if (AcceptToMemoryPoolWithTime(chainparams, pool, tx, nTime, false /* bypass_limits */,
+                                               false /* test_accept */).m_result_type == MempoolAcceptResult::ResultType::VALID) {
                     ++count;
                 } else {
                     // mempool may contain the transaction already, e.g. from