[refactor] move package checks into helper functions

This allows IsSorted() and IsConsistent() to be used by themselves.
IsSorted() with a precomputed set is used so that we don't create this
set multiple times.

Author: glozow

src/policy/packages.cpp

@@ -6,16 +6,77 @@
 #include <policy/policy.h>
 #include <primitives/transaction.h>
 #include <uint256.h>
-#include <util/hasher.h>
+#include <util/check.h>
 
 #include <algorithm>
 #include <cassert>
 #include <iterator>
 #include <memory>
 #include <numeric>
-#include <unordered_set>
 
-bool CheckPackage(const Package& txns, PackageValidationState& state)
+/** IsTopoSortedPackage where a set of txids has been pre-populated. The set is assumed to be correct and
+ * is mutated within this function (even if return value is false). */
+bool IsTopoSortedPackage(const Package& txns, std::unordered_set<uint256, SaltedTxidHasher>& later_txids)
+{
+    // Avoid misusing this function: later_txids should contain the txids of txns.
+    Assume(txns.size() == later_txids.size());
+
+    // later_txids always contains the txids of this transaction and the ones that come later in
+    // txns. If any transaction's input spends a tx in that set, we've found a parent placed later
+    // than its child.
+    for (const auto& tx : txns) {
+        for (const auto& input : tx->vin) {
+            if (later_txids.find(input.prevout.hash) != later_txids.end()) {
+                // The parent is a subsequent transaction in the package.
+                return false;
+            }
+        }
+        // Avoid misusing this function: later_txids must contain every tx.
+        Assume(later_txids.erase(tx->GetHash()) == 1);
+    }
+
+    // Avoid misusing this function: later_txids should have contained the txids of txns.
+    Assume(later_txids.empty());
+    return true;
+}
+
+bool IsTopoSortedPackage(const Package& txns)
+{
+    std::unordered_set<uint256, SaltedTxidHasher> later_txids;
+    std::transform(txns.cbegin(), txns.cend(), std::inserter(later_txids, later_txids.end()),
+                   [](const auto& tx) { return tx->GetHash(); });
+
+    return IsTopoSortedPackage(txns, later_txids);
+}
+
+bool IsConsistentPackage(const Package& txns)
+{
+    // Don't allow any conflicting transactions, i.e. spending the same inputs, in a package.
+    std::unordered_set<COutPoint, SaltedOutpointHasher> inputs_seen;
+    for (const auto& tx : txns) {
+        if (tx->vin.empty()) {
+            // This function checks consistency based on inputs, and we can't do that if there are
+            // no inputs. Duplicate empty transactions are also not consistent with one another.
+            // This doesn't create false negatives, as unconfirmed transactions are not allowed to
+            // have no inputs.
+            return false;
+        }
+        for (const auto& input : tx->vin) {
+            if (inputs_seen.find(input.prevout) != inputs_seen.end()) {
+                // This input is also present in another tx in the package.
+                return false;
+            }
+        }
+        // Batch-add all the inputs for a tx at a time. If we added them 1 at a time, we could
+        // catch duplicate inputs within a single tx.  This is a more severe, consensus error,
+        // and we want to report that from CheckTransaction instead.
+        std::transform(tx->vin.cbegin(), tx->vin.cend(), std::inserter(inputs_seen, inputs_seen.end()),
+                       [](const auto& input) { return input.prevout; });
+    }
+    return true;
+}
+
+bool CheckPackage(const Package& txns, PackageValidationState& state, bool require_sorted)
 {
     const unsigned int package_count = txns.size();
 
@@ -30,10 +91,6 @@ bool CheckPackage(const Package& txns, PackageValidationState& state)
         return state.Invalid(PackageValidationResult::PCKG_POLICY, "package-too-large");
     }
 
-    // Require the package to be sorted in order of dependency, i.e. parents appear before children.
-    // An unsorted package will fail anyway on missing-inputs, but it's better to quit earlier and
-    // fail on something less ambiguous (missing-inputs could also be an orphan or trying to
-    // spend nonexistent coins).
     std::unordered_set<uint256, SaltedTxidHasher> later_txids;
     std::transform(txns.cbegin(), txns.cend(), std::inserter(later_txids, later_txids.end()),
                    [](const auto& tx) { return tx->GetHash(); });
@@ -44,30 +101,17 @@ bool CheckPackage(const Package& txns, PackageValidationState& state)
         return state.Invalid(PackageValidationResult::PCKG_POLICY, "package-contains-duplicates");
     }
 
-    for (const auto& tx : txns) {
-        for (const auto& input : tx->vin) {
-            if (later_txids.find(input.prevout.hash) != later_txids.end()) {
-                // The parent is a subsequent transaction in the package.
-                return state.Invalid(PackageValidationResult::PCKG_POLICY, "package-not-sorted");
-            }
-        }
-        later_txids.erase(tx->GetHash());
+    // Require the package to be sorted in order of dependency, i.e. parents appear before children.
+    // An unsorted package will fail anyway on missing-inputs, but it's better to quit earlier and
+    // fail on something less ambiguous (missing-inputs could also be an orphan or trying to
+    // spend nonexistent coins).
+    if (require_sorted && !IsTopoSortedPackage(txns, later_txids)) {
+        return state.Invalid(PackageValidationResult::PCKG_POLICY, "package-not-sorted");
     }
 
     // Don't allow any conflicting transactions, i.e. spending the same inputs, in a package.
-    std::unordered_set<COutPoint, SaltedOutpointHasher> inputs_seen;
-    for (const auto& tx : txns) {
-        for (const auto& input : tx->vin) {
-            if (inputs_seen.find(input.prevout) != inputs_seen.end()) {
-                // This input is also present in another tx in the package.
-                return state.Invalid(PackageValidationResult::PCKG_POLICY, "conflict-in-package");
-            }
-        }
-        // Batch-add all the inputs for a tx at a time. If we added them 1 at a time, we could
-        // catch duplicate inputs within a single tx.  This is a more severe, consensus error,
-        // and we want to report that from CheckTransaction instead.
-        std::transform(tx->vin.cbegin(), tx->vin.cend(), std::inserter(inputs_seen, inputs_seen.end()),
-                       [](const auto& input) { return input.prevout; });
+    if (!IsConsistentPackage(txns)) {
+        return state.Invalid(PackageValidationResult::PCKG_POLICY, "conflict-in-package");
     }
     return true;
 }

src/policy/packages.h

@@ -9,8 +9,10 @@
 #include <consensus/validation.h>
 #include <policy/policy.h>
 #include <primitives/transaction.h>
+#include <util/hasher.h>
 
 #include <cstdint>
+#include <unordered_set>
 #include <vector>
 
 /** Default maximum number of transactions in a package. */
@@ -49,13 +51,32 @@ using Package = std::vector<CTransactionRef>;
 
 class PackageValidationState : public ValidationState<PackageValidationResult> {};
 
+/** If any direct dependencies exist between transactions (i.e. a child spending the output of a
+ * parent), checks that all parents appear somewhere in the list before their respective children.
+ * No other ordering is enforced. This function cannot detect indirect dependencies (e.g. a
+ * transaction's grandparent if its parent is not present).
+ * @returns true if sorted. False if any tx spends the output of a tx that appears later in txns.
+ */
+bool IsTopoSortedPackage(const Package& txns);
+
+/** Checks that these transactions don't conflict, i.e., spend the same prevout. This includes
+ * checking that there are no duplicate transactions. Since these checks require looking at the inputs
+ * of a transaction, returns false immediately if any transactions have empty vin.
+ *
+ * Does not check consistency of a transaction with oneself; does not check if a transaction spends
+ * the same prevout multiple times (see bad-txns-inputs-duplicate in CheckTransaction()).
+ *
+ * @returns true if there are no conflicts. False if any two transactions spend the same prevout.
+ * */
+bool IsConsistentPackage(const Package& txns);
+
 /** Context-free package policy checks:
  * 1. The number of transactions cannot exceed MAX_PACKAGE_COUNT.
  * 2. The total weight cannot exceed MAX_PACKAGE_WEIGHT.
  * 3. If any dependencies exist between transactions, parents must appear before children.
  * 4. Transactions cannot conflict, i.e., spend the same inputs.
  */
-bool CheckPackage(const Package& txns, PackageValidationState& state);
+bool CheckPackage(const Package& txns, PackageValidationState& state, bool require_sorted);
 
 /** Context-free check that a package is exactly one child and its parents; not all parents need to
  * be present, but the package must not contain any transactions that are not the child's parents.

src/test/txpackage_tests.cpp

@@ -9,6 +9,7 @@
 #include <primitives/transaction.h>
 #include <script/script.h>
 #include <test/util/random.h>
+#include <test/util/script.h>
 #include <test/util/setup_common.h>
 #include <validation.h>
 
@@ -47,7 +48,7 @@ BOOST_FIXTURE_TEST_CASE(package_sanitization_tests, TestChain100Setup)
         package_too_many.emplace_back(create_placeholder_tx(1, 1));
     }
     PackageValidationState state_too_many;
-    BOOST_CHECK(!CheckPackage(package_too_many, state_too_many));
+    BOOST_CHECK(!CheckPackage(package_too_many, state_too_many, /*require_sorted=*/true));
     BOOST_CHECK_EQUAL(state_too_many.GetResult(), PackageValidationResult::PCKG_POLICY);
     BOOST_CHECK_EQUAL(state_too_many.GetRejectReason(), "package-too-many-transactions");
 
@@ -62,7 +63,7 @@ BOOST_FIXTURE_TEST_CASE(package_sanitization_tests, TestChain100Setup)
     }
     BOOST_CHECK(package_too_large.size() <= MAX_PACKAGE_COUNT);
     PackageValidationState state_too_large;
-    BOOST_CHECK(!CheckPackage(package_too_large, state_too_large));
+    BOOST_CHECK(!CheckPackage(package_too_large, state_too_large, /*require_sorted=*/true));
     BOOST_CHECK_EQUAL(state_too_large.GetResult(), PackageValidationResult::PCKG_POLICY);
     BOOST_CHECK_EQUAL(state_too_large.GetRejectReason(), "package-too-large");
 
@@ -73,9 +74,39 @@ BOOST_FIXTURE_TEST_CASE(package_sanitization_tests, TestChain100Setup)
         package_duplicate_txids_empty.emplace_back(MakeTransactionRef(empty_tx));
     }
     PackageValidationState state_duplicates;
-    BOOST_CHECK(!CheckPackage(package_duplicate_txids_empty, state_duplicates));
+    BOOST_CHECK(!CheckPackage(package_duplicate_txids_empty, state_duplicates, /*require_sorted=*/true));
     BOOST_CHECK_EQUAL(state_duplicates.GetResult(), PackageValidationResult::PCKG_POLICY);
     BOOST_CHECK_EQUAL(state_duplicates.GetRejectReason(), "package-contains-duplicates");
+    BOOST_CHECK(!IsConsistentPackage(package_duplicate_txids_empty));
+
+    // Packages can't have transactions spending the same prevout
+    CMutableTransaction tx_zero_1;
+    CMutableTransaction tx_zero_2;
+    COutPoint same_prevout{InsecureRand256(), 0};
+    tx_zero_1.vin.emplace_back(same_prevout);
+    tx_zero_2.vin.emplace_back(same_prevout);
+    // Different vouts (not the same tx)
+    tx_zero_1.vout.emplace_back(CENT, P2WSH_OP_TRUE);
+    tx_zero_2.vout.emplace_back(2 * CENT, P2WSH_OP_TRUE);
+    Package package_conflicts{MakeTransactionRef(tx_zero_1), MakeTransactionRef(tx_zero_2)};
+    BOOST_CHECK(!IsConsistentPackage(package_conflicts));
+    // Transactions are considered sorted when they have no dependencies.
+    BOOST_CHECK(IsTopoSortedPackage(package_conflicts));
+    PackageValidationState state_conflicts;
+    BOOST_CHECK(!CheckPackage(package_conflicts, state_conflicts, /*require_sorted=*/true));
+    BOOST_CHECK_EQUAL(state_conflicts.GetResult(), PackageValidationResult::PCKG_POLICY);
+    BOOST_CHECK_EQUAL(state_conflicts.GetRejectReason(), "conflict-in-package");
+
+    // IsConsistentPackage only cares about conflicts between transactions, not about a transaction
+    // conflicting with itself (i.e. duplicate prevouts in vin).
+    CMutableTransaction dup_tx;
+    const COutPoint rand_prevout{InsecureRand256(), 0};
+    dup_tx.vin.emplace_back(rand_prevout);
+    dup_tx.vin.emplace_back(rand_prevout);
+    Package package_with_dup_tx{MakeTransactionRef(dup_tx)};
+    BOOST_CHECK(IsConsistentPackage(package_with_dup_tx));
+    package_with_dup_tx.emplace_back(create_placeholder_tx(1, 1));
+    BOOST_CHECK(IsConsistentPackage(package_with_dup_tx));
 }
 
 BOOST_FIXTURE_TEST_CASE(package_validation_tests, TestChain100Setup)
@@ -157,8 +188,8 @@ BOOST_FIXTURE_TEST_CASE(noncontextual_package_tests, TestChain100Setup)
         CTransactionRef tx_child = MakeTransactionRef(mtx_child);
 
         PackageValidationState state;
-        BOOST_CHECK(CheckPackage({tx_parent, tx_child}, state));
-        BOOST_CHECK(!CheckPackage({tx_child, tx_parent}, state));
+        BOOST_CHECK(CheckPackage({tx_parent, tx_child}, state, /*require_sorted=*/true));
+        BOOST_CHECK(!CheckPackage({tx_child, tx_parent}, state, /*require_sorted=*/true));
         BOOST_CHECK_EQUAL(state.GetResult(), PackageValidationResult::PCKG_POLICY);
         BOOST_CHECK_EQUAL(state.GetRejectReason(), "package-not-sorted");
         BOOST_CHECK(IsChildWithParents({tx_parent, tx_child}));
@@ -186,7 +217,7 @@ BOOST_FIXTURE_TEST_CASE(noncontextual_package_tests, TestChain100Setup)
         package.push_back(MakeTransactionRef(child));
 
         PackageValidationState state;
-        BOOST_CHECK(CheckPackage(package, state));
+        BOOST_CHECK(CheckPackage(package, state, /*require_sorted=*/true));
         BOOST_CHECK(IsChildWithParents(package));
         BOOST_CHECK(IsChildWithParentsTree(package));
 
@@ -224,8 +255,8 @@ BOOST_FIXTURE_TEST_CASE(noncontextual_package_tests, TestChain100Setup)
         BOOST_CHECK(!IsChildWithParentsTree({tx_parent, tx_parent_also_child, tx_child}));
         // IsChildWithParents does not detect unsorted parents.
         BOOST_CHECK(IsChildWithParents({tx_parent_also_child, tx_parent, tx_child}));
-        BOOST_CHECK(CheckPackage({tx_parent, tx_parent_also_child, tx_child}, state));
-        BOOST_CHECK(!CheckPackage({tx_parent_also_child, tx_parent, tx_child}, state));
+        BOOST_CHECK(CheckPackage({tx_parent, tx_parent_also_child, tx_child}, state, /*require_sorted=*/true));
+        BOOST_CHECK(!CheckPackage({tx_parent_also_child, tx_parent, tx_child}, state, /*require_sorted=*/true));
         BOOST_CHECK_EQUAL(state.GetResult(), PackageValidationResult::PCKG_POLICY);
         BOOST_CHECK_EQUAL(state.GetRejectReason(), "package-not-sorted");
     }

src/validation.cpp

@@ -1258,7 +1258,7 @@ PackageMempoolAcceptResult MemPoolAccept::AcceptMultipleTransactions(const std::
 
     // These context-free package limits can be done before taking the mempool lock.
     PackageValidationState package_state;
-    if (!CheckPackage(txns, package_state)) return PackageMempoolAcceptResult(package_state, {});
+    if (!CheckPackage(txns, package_state, /*require_sorted=*/true)) return PackageMempoolAcceptResult(package_state, {});
 
     std::vector<Workspace> workspaces{};
     workspaces.reserve(txns.size());
@@ -1405,7 +1405,9 @@ PackageMempoolAcceptResult MemPoolAccept::AcceptPackage(const Package& package,
     // transactions and thus won't return any MempoolAcceptResults, just a package-wide error.
 
     // Context-free package checks.
-    if (!CheckPackage(package, package_state_quit_early)) return PackageMempoolAcceptResult(package_state_quit_early, {});
+    if (!CheckPackage(package, package_state_quit_early, /*require_sorted=*/true)) {
+        return PackageMempoolAcceptResult(package_state_quit_early, {});
+    }
 
     // All transactions in the package must be a parent of the last transaction. This is just an
     // opportunity for us to fail fast on a context-free check without taking the mempool lock.