From 876a05dc9dbef9ec4f5f1e56e0c413556bde9f06 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 rbf invariants

---
 src/test/util/txmempool.cpp | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/src/test/util/txmempool.cpp b/src/test/util/txmempool.cpp
index 379c3c9329a92d..0e3f9e72cf8a01 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 <txmempool.h>
 #include <util/check.h>
 #include <util/time.h>
@@ -66,10 +67,24 @@ std::optional<std::string> CheckPackageMempoolAcceptResult(const Package& txns,
             return strprintf("tx %s unexpectedly failed: %s", wtxid.ToString(), atmp_result.m_state.ToString());
         }
 
-        //m_replaced_transactions should exist iff the result was VALID
-        if (atmp_result.m_replaced_transactions.has_value() != valid) {
-            return strprintf("tx %s result should %shave m_replaced_transactions",
+        if (atmp_result.m_replaced_transactions.has_value()) {
+            // m_replaced_transactions should exist iff the result was VALID
+            if (!valid) {
+                return strprintf("tx %s result should %shave m_replaced_transactions",
                                     wtxid.ToString(), valid ? "" : "not ");
+            }
+            // Each subpackage is allowed MAX_REPLACEMENT_CANDIDATES replacements (only checking individually here)
+            if (atmp_result.m_replaced_transactions.value().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.value().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());
+            }
         }
 
         // m_vsize and m_base_fees should exist iff the result was VALID or MEMPOOL_ENTRY
@@ -112,6 +127,13 @@ std::optional<std::string> CheckPackageMempoolAcceptResult(const Package& txns,
                     return strprintf("wtxid %s should not be in mempool", wtxid.ToString());
                 }
             }
+            if (atmp_result.m_replaced_transactions.has_value()) {
+                for (const auto& tx_ref : atmp_result.m_replaced_transactions.value()) {
+                    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;