[policy] add v3 policy rules

Co-authored-by: Suhas Daftuar <sdaftuar@gmail.com>

1 files changed, 83 insertions, 0 deletions

diff --git a/src/policy/v3_policy.h b/src/policy/v3_policy.h
new file mode 100644
index 0000000000..9e871915e5
--- /dev/null
+++ b/src/policy/v3_policy.h
@@ -0,0 +1,83 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_POLICY_V3_POLICY_H
+#define BITCOIN_POLICY_V3_POLICY_H
+
+#include <consensus/amount.h>
+#include <policy/packages.h>
+#include <policy/policy.h>
+#include <primitives/transaction.h>
+#include <txmempool.h>
+#include <util/result.h>
+
+#include <set>
+#include <string>
+
+// This module enforces rules for transactions with nVersion=3 ("v3 transactions") which help make
+// RBF abilities more robust.
+
+// v3 only allows 1 parent and 1 child when unconfirmed.
+/** Maximum number of transactions including an unconfirmed tx and its descendants. */
+static constexpr unsigned int V3_DESCENDANT_LIMIT{2};
+/** Maximum number of transactions including a V3 tx and all its mempool ancestors. */
+static constexpr unsigned int V3_ANCESTOR_LIMIT{2};
+
+/** Maximum sigop-adjusted virtual size of a tx which spends from an unconfirmed v3 transaction. */
+static constexpr int64_t V3_CHILD_MAX_VSIZE{1000};
+// These limits are within the default ancestor/descendant limits.
+static_assert(V3_CHILD_MAX_VSIZE + MAX_STANDARD_TX_WEIGHT / WITNESS_SCALE_FACTOR <= DEFAULT_ANCESTOR_SIZE_LIMIT_KVB * 1000);
+static_assert(V3_CHILD_MAX_VSIZE + MAX_STANDARD_TX_WEIGHT / WITNESS_SCALE_FACTOR <= DEFAULT_DESCENDANT_SIZE_LIMIT_KVB * 1000);
+
+/** Must be called for every transaction, even if not v3. Not strictly necessary for transactions
+ * accepted through AcceptMultipleTransactions.
+ *
+ * Checks the following rules:
+ * 1. A v3 tx must only have v3 unconfirmed ancestors.
+ * 2. A non-v3 tx must only have non-v3 unconfirmed ancestors.
+ * 3. A v3's ancestor set, including itself, must be within V3_ANCESTOR_LIMIT.
+ * 4. A v3's descendant set, including itself, must be within V3_DESCENDANT_LIMIT.
+ * 5. If a v3 tx has any unconfirmed ancestors, the tx's sigop-adjusted vsize must be within
+ * V3_CHILD_MAX_VSIZE.
+ *
+ *
+ * @param[in]   mempool_ancestors       The in-mempool ancestors of ptx.
+ * @param[in]   direct_conflicts        In-mempool transactions this tx conflicts with. These conflicts
+ *                                      are used to more accurately calculate the resulting descendant
+ *                                      count of in-mempool ancestors.
+ * @param[in]   vsize                   The sigop-adjusted virtual size of ptx.
+ *
+ * @returns debug string if an error occurs, std::nullopt otherwise.
+ */
+std::optional<std::string> SingleV3Checks(const CTransactionRef& ptx,
+                                          const CTxMemPool::setEntries& mempool_ancestors,
+                                          const std::set<Txid>& direct_conflicts,
+                                          int64_t vsize);
+
+/** Must be called for every transaction that is submitted within a package, even if not v3.
+ *
+ * For each transaction in a package:
+ * If it's not a v3 transaction, verify it has no direct v3 parents in the mempool or the package.
+
+ * If it is a v3 transaction, verify that any direct parents in the mempool or the package are v3.
+ * If such a parent exists, verify that parent has no other children in the package or the mempool,
+ * and that the transaction itself has no children in the package.
+ *
+ * If any v3 violations in the package exist, this test will fail for one of them:
+ * - if a v3 transaction T has a parent in the mempool and a child in the package, then PV3C(T) will fail
+ * - if a v3 transaction T has a parent in the package and a child in the package, then PV3C(T) will fail
+ * - if a v3 transaction T and a v3 (sibling) transaction U have some parent in the mempool,
+ *   then PV3C(T) and PV3C(U) will fail
+ * - if a v3 transaction T and a v3 (sibling) transaction U have some parent in the package,
+ *   then PV3C(T) and PV3C(U) will fail
+ * - if a v3 transaction T has a parent P and a grandparent G in the package, then
+ *   PV3C(P) will fail (though PV3C(G) and PV3C(T) might succeed).
+ *
+ * @returns debug string if an error occurs, std::nullopt otherwise.
+ * */
+std::optional<std::string> PackageV3Checks(const CTransactionRef& ptx, int64_t vsize,
+                                           const Package& package,
+                                           const CTxMemPool::setEntries& mempool_ancestors);
+
+#endif // BITCOIN_POLICY_V3_POLICY_H