validation: Use vector of outputs instead of CCoinsViewCache in CheckInputScripts

Move the responsibility of retrieving coins from the CCoinsViewCache
in CheckInputScripts to its caller.

Add a helper method in CCoinsViewCache to collect all Coin's outputs
spent by a transaction's inputs.

Callers of CCoinsViewCache are updated to either pre-fetch the spent
outputs, or pass in an empty vector if the precomputed transaction data
has already been initialized with the required outputs.

This is a part of a series of commits for removing access to the
CCoinsViewCache in consensus verification functions. The goal is to
allow calling verification functions with pre-fetched, or a user-defined
set of coins.

src/coins.cpp

@@ -170,6 +170,19 @@ std::vector<std::reference_wrapper<const Coin>> CCoinsViewCache::AccessCoins(con
     return coins;
 }
 
+std::vector<CTxOut> CCoinsViewCache::GetUnspentOutputs(const CTransaction& tx) const
+{
+    std::vector<CTxOut> spent_outputs;
+    spent_outputs.reserve(tx.vin.size());
+    for (const auto& txin : tx.vin) {
+        const COutPoint& prevout = txin.prevout;
+        const Coin& coin = AccessCoin(prevout);
+        assert(!coin.IsSpent());
+        spent_outputs.emplace_back(coin.out);
+    }
+    return spent_outputs;
+}
+
 bool CCoinsViewCache::HaveCoin(const COutPoint &outpoint) const {
     CCoinsMap::const_iterator it = FetchCoin(outpoint);
     return (it != cacheCoins.end() && !it->second.coin.IsSpent());

src/coins.h

@@ -424,6 +424,13 @@ public:
      */
     std::vector<std::reference_wrapper<const Coin>> AccessCoins(const CTransaction& tx) const;
 
+    /**
+     * Return a vector of unspent outputs of coins in the cache that are spent
+     * by the provided transaction. The coins they belong to must be unspent in
+     * the cache.
+     */
+    std::vector<CTxOut> GetUnspentOutputs(const CTransaction& tx) const;
+
     /**
      * Add a coin. Set possible_overwrite to true if an unspent version may
      * already exist in the cache.

src/test/txvalidationcache_tests.cpp

@@ -21,7 +21,7 @@ struct Dersig100Setup : public TestChain100Setup {
 };
 
 bool CheckInputScripts(const CTransaction& tx, TxValidationState& state,
-                       const CCoinsViewCache& inputs, unsigned int flags, bool cacheSigStore,
+                       std::vector<CTxOut>&& spent_outputs, unsigned int flags, bool cacheSigStore,
                        bool cacheFullScriptStore, PrecomputedTransactionData& txdata,
                        ValidationCache& validation_cache,
                        std::vector<CScriptCheck>* pvChecks) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
@@ -124,6 +124,9 @@ static void ValidateCheckInputsForAllFlags(const CTransaction &tx, uint32_t fail
 {
     PrecomputedTransactionData txdata;
 
+    std::vector<CTxOut> spent_outputs{active_coins_tip.GetUnspentOutputs(tx)};
+    txdata.Init(tx, std::move(spent_outputs));
+
     FastRandomContext insecure_rand(true);
 
     for (int count = 0; count < 10000; ++count) {
@@ -142,7 +145,7 @@ static void ValidateCheckInputsForAllFlags(const CTransaction &tx, uint32_t fail
             // WITNESS requires P2SH
             test_flags |= SCRIPT_VERIFY_P2SH;
         }
-        bool ret = CheckInputScripts(tx, state, &active_coins_tip, test_flags, true, add_to_cache, txdata, validation_cache, nullptr);
+        bool ret = CheckInputScripts(tx, state, {}, test_flags, true, add_to_cache, txdata, validation_cache, nullptr);
         // CheckInputScripts should succeed iff test_flags doesn't intersect with
         // failing_flags
         bool expected_return_value = !(test_flags & failing_flags);
@@ -152,13 +155,13 @@ static void ValidateCheckInputsForAllFlags(const CTransaction &tx, uint32_t fail
         if (ret && add_to_cache) {
             // Check that we get a cache hit if the tx was valid
             std::vector<CScriptCheck> scriptchecks;
-            BOOST_CHECK(CheckInputScripts(tx, state, &active_coins_tip, test_flags, true, add_to_cache, txdata, validation_cache, &scriptchecks));
+            BOOST_CHECK(CheckInputScripts(tx, state, {}, test_flags, true, add_to_cache, txdata, validation_cache, &scriptchecks));
             BOOST_CHECK(scriptchecks.empty());
         } else {
             // Check that we get script executions to check, if the transaction
             // was invalid, or we didn't add to cache.
             std::vector<CScriptCheck> scriptchecks;
-            BOOST_CHECK(CheckInputScripts(tx, state, &active_coins_tip, test_flags, true, add_to_cache, txdata, validation_cache, &scriptchecks));
+            BOOST_CHECK(CheckInputScripts(tx, state, {}, test_flags, true, add_to_cache, txdata, validation_cache, &scriptchecks));
             BOOST_CHECK_EQUAL(scriptchecks.size(), tx.vin.size());
         }
     }
@@ -216,13 +219,16 @@ BOOST_FIXTURE_TEST_CASE(checkinputs_test, Dersig100Setup)
         TxValidationState state;
         PrecomputedTransactionData ptd_spend_tx;
 
-        BOOST_CHECK(!CheckInputScripts(CTransaction(spend_tx), state, &m_node.chainman->ActiveChainstate().CoinsTip(), SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_DERSIG, true, true, ptd_spend_tx, m_node.chainman->m_validation_cache, nullptr));
+        std::vector<CTxOut> spent_outputs{m_node.chainman->ActiveChainstate().CoinsTip().GetUnspentOutputs(CTransaction(spend_tx))};
+        ptd_spend_tx.Init(spend_tx, std::move(spent_outputs));
+
+        BOOST_CHECK(!CheckInputScripts(CTransaction(spend_tx), state, {}, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_DERSIG, true, true, ptd_spend_tx, m_node.chainman->m_validation_cache, nullptr));
 
         // If we call again asking for scriptchecks (as happens in
         // ConnectBlock), we should add a script check object for this -- we're
         // not caching invalidity (if that changes, delete this test case).
         std::vector<CScriptCheck> scriptchecks;
-        BOOST_CHECK(CheckInputScripts(CTransaction(spend_tx), state, &m_node.chainman->ActiveChainstate().CoinsTip(), SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_DERSIG, true, true, ptd_spend_tx, m_node.chainman->m_validation_cache, &scriptchecks));
+        BOOST_CHECK(CheckInputScripts(CTransaction(spend_tx), state, {}, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_DERSIG, true, true, ptd_spend_tx, m_node.chainman->m_validation_cache, &scriptchecks));
         BOOST_CHECK_EQUAL(scriptchecks.size(), 1U);
 
         // Test that CheckInputScripts returns true iff DERSIG-enforcing flags are
@@ -284,7 +290,10 @@ BOOST_FIXTURE_TEST_CASE(checkinputs_test, Dersig100Setup)
         invalid_with_cltv_tx.vin[0].scriptSig = CScript() << vchSig << 100;
         TxValidationState state;
         PrecomputedTransactionData txdata;
-        BOOST_CHECK(CheckInputScripts(CTransaction(invalid_with_cltv_tx), state, m_node.chainman->ActiveChainstate().CoinsTip(), SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, true, true, txdata, m_node.chainman->m_validation_cache, nullptr));
+        std::vector<CTxOut> spent_outputs{m_node.chainman->ActiveChainstate().CoinsTip().GetUnspentOutputs(CTransaction(invalid_with_cltv_tx))};
+        txdata.Init(invalid_with_cltv_tx, std::move(spent_outputs));
+
+        BOOST_CHECK(CheckInputScripts(CTransaction(invalid_with_cltv_tx), state, {}, SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, true, true, txdata, m_node.chainman->m_validation_cache, nullptr));
     }
 
     // TEST CHECKSEQUENCEVERIFY
@@ -312,7 +321,10 @@ BOOST_FIXTURE_TEST_CASE(checkinputs_test, Dersig100Setup)
         invalid_with_csv_tx.vin[0].scriptSig = CScript() << vchSig << 100;
         TxValidationState state;
         PrecomputedTransactionData txdata;
-        BOOST_CHECK(CheckInputScripts(CTransaction(invalid_with_csv_tx), state, &m_node.chainman->ActiveChainstate().CoinsTip(), SCRIPT_VERIFY_CHECKSEQUENCEVERIFY, true, true, txdata, m_node.chainman->m_validation_cache, nullptr));
+        std::vector<CTxOut> spent_outputs{m_node.chainman->ActiveChainstate().CoinsTip().GetUnspentOutputs(CTransaction(invalid_with_csv_tx))};
+        txdata.Init(invalid_with_csv_tx, std::move(spent_outputs));
+
+        BOOST_CHECK(CheckInputScripts(CTransaction(invalid_with_csv_tx), state, {}, SCRIPT_VERIFY_CHECKSEQUENCEVERIFY, true, true, txdata, m_node.chainman->m_validation_cache, nullptr));
     }
 
     // TODO: add tests for remaining script flags
@@ -373,13 +385,16 @@ BOOST_FIXTURE_TEST_CASE(checkinputs_test, Dersig100Setup)
 
         TxValidationState state;
         PrecomputedTransactionData txdata;
+        std::vector<CTxOut> spent_outputs{m_node.chainman->ActiveChainstate().CoinsTip().GetUnspentOutputs(CTransaction(tx))};
+        txdata.Init(tx, std::move(spent_outputs));
+
         // This transaction is now invalid under segwit, because of the second input.
-        BOOST_CHECK(!CheckInputScripts(CTransaction(tx), state, &m_node.chainman->ActiveChainstate().CoinsTip(), SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS, true, true, txdata, m_node.chainman->m_validation_cache, nullptr));
+        BOOST_CHECK(!CheckInputScripts(CTransaction(tx), state, {}, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS, true, true, txdata, m_node.chainman->m_validation_cache, nullptr));
 
         std::vector<CScriptCheck> scriptchecks;
         // Make sure this transaction was not cached (ie because the first
         // input was valid)
-        BOOST_CHECK(CheckInputScripts(CTransaction(tx), state, &m_node.chainman->ActiveChainstate().CoinsTip(), SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS, true, true, txdata, m_node.chainman->m_validation_cache, &scriptchecks));
+        BOOST_CHECK(CheckInputScripts(CTransaction(tx), state, {}, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS, true, true, txdata, m_node.chainman->m_validation_cache, &scriptchecks));
         // Should get 2 script checks back -- caching is on a whole-transaction basis.
         BOOST_CHECK_EQUAL(scriptchecks.size(), 2U);
     }

src/validation.cpp

@@ -137,11 +137,11 @@ const CBlockIndex* Chainstate::FindForkInGlobalIndex(const CBlockLocator& locato
 }
 
 bool CheckInputScripts(const CTransaction& tx, TxValidationState& state,
-                       const CCoinsViewCache& inputs, unsigned int flags, bool cacheSigStore,
+                       std::vector<CTxOut>&& spent_outputs, unsigned int flags, bool cacheSigStore,
                        bool cacheFullScriptStore, PrecomputedTransactionData& txdata,
                        ValidationCache& validation_cache,
                        std::vector<CScriptCheck>* pvChecks = nullptr)
-                       EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
 bool CheckFinalTxAtTip(const CBlockIndex& active_chain_tip, const CTransaction& tx)
 {
@@ -428,8 +428,10 @@ static bool CheckInputsFromMempoolAndCache(const CTransaction& tx, TxValidationS
         }
     }
 
+    std::vector<CTxOut> spent_outputs{view.GetUnspentOutputs(tx)};
+
     // Call CheckInputScripts() to cache signature and script validity against current tip consensus rules.
-    return CheckInputScripts(tx, state, view, flags, /* cacheSigStore= */ true, /* cacheFullScriptStore= */ true, txdata, validation_cache);
+    return CheckInputScripts(tx, state, std::move(spent_outputs), flags, /* cacheSigStore= */ true, /* cacheFullScriptStore= */ true, txdata, validation_cache);
 }
 
 namespace {
@@ -1234,15 +1236,17 @@ bool MemPoolAccept::PolicyScriptChecks(const ATMPArgs& args, Workspace& ws)
 
     constexpr unsigned int scriptVerifyFlags = STANDARD_SCRIPT_VERIFY_FLAGS;
 
+    std::vector<CTxOut> spent_outputs{m_view.GetUnspentOutputs(tx)};
+
     // Check input scripts and signatures.
     // This is done last to help prevent CPU exhaustion denial-of-service attacks.
-    if (!CheckInputScripts(tx, state, m_view, scriptVerifyFlags, true, false, ws.m_precomputed_txdata, GetValidationCache())) {
+    if (!CheckInputScripts(tx, state, std::move(spent_outputs), scriptVerifyFlags, true, false, ws.m_precomputed_txdata, GetValidationCache())) {
         // SCRIPT_VERIFY_CLEANSTACK requires SCRIPT_VERIFY_WITNESS, so we
         // need to turn both off, and compare against just turning off CLEANSTACK
         // to see if the failure is specifically due to witness validation.
         TxValidationState state_dummy; // Want reported failures to be from first CheckInputScripts
-        if (!tx.HasWitness() && CheckInputScripts(tx, state_dummy, m_view, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, false, ws.m_precomputed_txdata, GetValidationCache()) &&
+        if (!tx.HasWitness() && CheckInputScripts(tx, state_dummy, {}, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, false, ws.m_precomputed_txdata, GetValidationCache()) &&
-                !CheckInputScripts(tx, state_dummy, m_view, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, false, ws.m_precomputed_txdata, GetValidationCache())) {
+            !CheckInputScripts(tx, state_dummy, {}, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, false, ws.m_precomputed_txdata, GetValidationCache())) {
             // Only the witness is missing, so the transaction itself may be fine.
             state.Invalid(TxValidationResult::TX_WITNESS_STRIPPED,
                     state.GetRejectReason(), state.GetDebugMessage());
@@ -2162,7 +2166,7 @@ ValidationCache::ValidationCache(const size_t script_execution_cache_bytes, cons
  * Non-static (and redeclared) in src/test/txvalidationcache_tests.cpp
  */
 bool CheckInputScripts(const CTransaction& tx, TxValidationState& state,
-                       const CCoinsViewCache& inputs, unsigned int flags, bool cacheSigStore,
+                       std::vector<CTxOut>&& spent_outputs, unsigned int flags, bool cacheSigStore,
                        bool cacheFullScriptStore, PrecomputedTransactionData& txdata,
                        ValidationCache& validation_cache,
                        std::vector<CScriptCheck>* pvChecks)
@@ -2187,15 +2191,6 @@ bool CheckInputScripts(const CTransaction& tx, TxValidationState& state,
     }
 
     if (!txdata.m_spent_outputs_ready) {
-        std::vector<CTxOut> spent_outputs;
-        spent_outputs.reserve(tx.vin.size());
-
-        for (const auto& txin : tx.vin) {
-            const COutPoint& prevout = txin.prevout;
-            const Coin& coin = inputs.AccessCoin(prevout);
-            assert(!coin.IsSpent());
-            spent_outputs.emplace_back(coin.out);
-        }
         txdata.Init(tx, std::move(spent_outputs));
     }
     assert(txdata.m_spent_outputs.size() == tx.vin.size());
@@ -2703,7 +2698,10 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
             std::vector<CScriptCheck> vChecks;
             bool fCacheResults = fJustCheck; /* Don't cache results if we're actually connecting blocks (still consult the cache, though) */
             TxValidationState tx_state;
-            if (fScriptChecks && !CheckInputScripts(tx, tx_state, view, flags, fCacheResults, fCacheResults, txsdata[i], m_chainman.m_validation_cache, parallel_script_checks ? &vChecks : nullptr)) {
+
+            std::vector<CTxOut> spent_outputs{view.GetUnspentOutputs(tx)};
+
+            if (fScriptChecks && !CheckInputScripts(tx, tx_state, std::move(spent_outputs), flags, fCacheResults, fCacheResults, txsdata[i], m_chainman.m_validation_cache, parallel_script_checks ? &vChecks : nullptr)) {
                 // Any transaction validation failure in ConnectBlock is a block consensus failure
                 state.Invalid(BlockValidationResult::BLOCK_CONSENSUS,
                               tx_state.GetRejectReason(), tx_state.GetDebugMessage());