From d3466e4cc5051c314873dd14ec8f7a88494c0780 Mon Sep 17 00:00:00 2001
From: Greg Sanders <gsanders87@gmail.com>
Date: Thu, 7 Dec 2023 16:48:06 -0500
Subject: [PATCH] CheckPackageMempoolAcceptResult: Check package rbf invariants

---
 src/test/util/txmempool.cpp | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/src/test/util/txmempool.cpp b/src/test/util/txmempool.cpp
index 4dfc09ef676..298e33f5a96 100644
--- a/src/test/util/txmempool.cpp
+++ b/src/test/util/txmempool.cpp
@@ -7,6 +7,7 @@
 #include <chainparams.h>
 #include <node/context.h>
 #include <node/mempool_args.h>
+#include <policy/rbf.h>
 #include <policy/v3_policy.h>
 #include <txmempool.h>
 #include <util/check.h>
@@ -68,6 +69,28 @@ std::optional<std::string> CheckPackageMempoolAcceptResult(const Package& txns,
             return strprintf("tx %s unexpectedly failed: %s", wtxid.ToString(), atmp_result.m_state.ToString());
         }
 
+        // Each subpackage is allowed MAX_REPLACEMENT_CANDIDATES replacements (only checking individually here)
+        if (atmp_result.m_replaced_transactions.size() > MAX_REPLACEMENT_CANDIDATES) {
+            return strprintf("tx %s result replaced too many transactions",
+                                wtxid.ToString());
+        }
+
+        // Replacements can't happen for subpackages larger than 2
+        if (!atmp_result.m_replaced_transactions.empty() &&
+            atmp_result.m_wtxids_fee_calculations.has_value() && atmp_result.m_wtxids_fee_calculations.value().size() > 2) {
+             return strprintf("tx %s was part of a too-large package RBF subpackage",
+                                wtxid.ToString());
+        }
+
+        if (!atmp_result.m_replaced_transactions.empty() && mempool) {
+            LOCK(mempool->cs);
+            // If replacements occurred and it used 2 transactions, this is a package RBF and should result in a cluster of size 2
+            if (atmp_result.m_wtxids_fee_calculations.has_value() && atmp_result.m_wtxids_fee_calculations.value().size() == 2) {
+                const auto cluster = mempool->GatherClusters({tx->GetHash()});
+                if (cluster.size() != 2) return strprintf("tx %s has too many ancestors or descendants for a package rbf", wtxid.ToString());
+            }
+        }
+
         // m_vsize and m_base_fees should exist iff the result was VALID or MEMPOOL_ENTRY
         const bool mempool_entry{atmp_result.m_result_type == MempoolAcceptResult::ResultType::MEMPOOL_ENTRY};
         if (atmp_result.m_base_fees.has_value() != (valid || mempool_entry)) {
@@ -108,6 +131,11 @@ std::optional<std::string> CheckPackageMempoolAcceptResult(const Package& txns,
                     return strprintf("wtxid %s should not be in mempool", wtxid.ToString());
                 }
             }
+            for (const auto& tx_ref : atmp_result.m_replaced_transactions) {
+                if (mempool->exists(GenTxid::Txid(tx_ref->GetHash()))) {
+                    return strprintf("tx %s should not be in mempool as it was replaced", tx_ref->GetWitnessHash().ToString());
+                }
+            }
         }
     }
     return std::nullopt;