Merge bitcoin/bitcoin#26103: refactor: mempool: use CTxMemPool::Limits

33b12e5df6aa14344dd084e0c6f2d34158fca383 docs: improve docs where MemPoolLimits is used (stickies-v)
6945853c0bf3b1941bfd18b5ffbd5a81be0e56da test: use NoLimits() in MempoolIndexingTest (stickies-v)
3a86f24a4c1e4e985b1d90eddc135b8dd17049a4 refactor: mempool: use CTxMempool::Limits (stickies-v)
b85af25f8770974bae4ef3fae64e75ef6dd2d3c2 refactor: mempool: add MemPoolLimits::NoLimits() (stickies-v)

Pull request description:

  Mempool currently considers 4 limits regarding ancestor and descendant count and size, which get passed around between functions quite a bit. This PR uses `CTxMemPool::Limits` introduced in https://github.com/bitcoin/bitcoin/pull/25290 to simplify those signatures and callsites.

  The purpose of this PR is to improve readability and maintenance, without behaviour change.

  As noted in the first commit "refactor: mempool: change MemPoolLimits members to uint", we currently have an underflow issue where a user could pass a negative `-limitancestorsize`, which is eventually cast to an unsigned integer. This behaviour already exists. Because it's orthogonal and to minimize scope, I think this should be fixed in a separate PR.

ACKs for top commit:
  hebasto:
    ACK 33b12e5df6aa14344dd084e0c6f2d34158fca383, I have reviewed the code and it looks OK, I agree it can be merged.
  glozow:
    reACK 33b12e5df6aa14344dd084e0c6f2d34158fca383

Tree-SHA512: 591c6dcee1894f1c3ca28b34a680eeadcf0d40cda92451b4a422c03087b27d682b5e30ba4367abd75a99b5ccb115b7884b0026958d3c7dddab030549db5a4056

1 files changed, 21 insertions, 36 deletions

diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 8a977b8126..84ed2e9ef5 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -187,10 +187,7 @@ bool CTxMemPool::CalculateAncestorsAndCheckLimits(size_t entry_size,
                                                   size_t entry_count,
                                                   setEntries& setAncestors,
                                                   CTxMemPoolEntry::Parents& staged_ancestors,
-                                                  uint64_t limitAncestorCount,
-                                                  uint64_t limitAncestorSize,
-                                                  uint64_t limitDescendantCount,
-                                                  uint64_t limitDescendantSize,
+                                                  const Limits& limits,
                                                   std::string &errString) const
 {
     size_t totalSizeWithAncestors = entry_size;
@@ -203,14 +200,14 @@ bool CTxMemPool::CalculateAncestorsAndCheckLimits(size_t entry_size,
         staged_ancestors.erase(stage);
         totalSizeWithAncestors += stageit->GetTxSize();
 
-        if (stageit->GetSizeWithDescendants() + entry_size > limitDescendantSize) {
-            errString = strprintf("exceeds descendant size limit for tx %s [limit: %u]", stageit->GetTx().GetHash().ToString(), limitDescendantSize);
+        if (stageit->GetSizeWithDescendants() + entry_size > static_cast<uint64_t>(limits.descendant_size_vbytes)) {
+            errString = strprintf("exceeds descendant size limit for tx %s [limit: %u]", stageit->GetTx().GetHash().ToString(), limits.descendant_size_vbytes);
             return false;
-        } else if (stageit->GetCountWithDescendants() + entry_count > limitDescendantCount) {
-            errString = strprintf("too many descendants for tx %s [limit: %u]", stageit->GetTx().GetHash().ToString(), limitDescendantCount);
+        } else if (stageit->GetCountWithDescendants() + entry_count > static_cast<uint64_t>(limits.descendant_count)) {
+            errString = strprintf("too many descendants for tx %s [limit: %u]", stageit->GetTx().GetHash().ToString(), limits.descendant_count);
             return false;
-        } else if (totalSizeWithAncestors > limitAncestorSize) {
-            errString = strprintf("exceeds ancestor size limit [limit: %u]", limitAncestorSize);
+        } else if (totalSizeWithAncestors > static_cast<uint64_t>(limits.ancestor_size_vbytes)) {
+            errString = strprintf("exceeds ancestor size limit [limit: %u]", limits.ancestor_size_vbytes);
             return false;
         }
 
@@ -222,8 +219,8 @@ bool CTxMemPool::CalculateAncestorsAndCheckLimits(size_t entry_size,
             if (setAncestors.count(parent_it) == 0) {
                 staged_ancestors.insert(parent);
             }
-            if (staged_ancestors.size() + setAncestors.size() + entry_count > limitAncestorCount) {
-                errString = strprintf("too many unconfirmed ancestors [limit: %u]", limitAncestorCount);
+            if (staged_ancestors.size() + setAncestors.size() + entry_count > static_cast<uint64_t>(limits.ancestor_count)) {
+                errString = strprintf("too many unconfirmed ancestors [limit: %u]", limits.ancestor_count);
                 return false;
             }
         }
@@ -233,10 +230,7 @@ bool CTxMemPool::CalculateAncestorsAndCheckLimits(size_t entry_size,
 }
 
 bool CTxMemPool::CheckPackageLimits(const Package& package,
-                                    uint64_t limitAncestorCount,
-                                    uint64_t limitAncestorSize,
-                                    uint64_t limitDescendantCount,
-                                    uint64_t limitDescendantSize,
+                                    const Limits& limits,
                                     std::string &errString) const
 {
     CTxMemPoolEntry::Parents staged_ancestors;
@@ -247,8 +241,8 @@ bool CTxMemPool::CheckPackageLimits(const Package& package,
             std::optional<txiter> piter = GetIter(input.prevout.hash);
             if (piter) {
                 staged_ancestors.insert(**piter);
-                if (staged_ancestors.size() + package.size() > limitAncestorCount) {
-                    errString = strprintf("too many unconfirmed parents [limit: %u]", limitAncestorCount);
+                if (staged_ancestors.size() + package.size() > static_cast<uint64_t>(limits.ancestor_count)) {
+                    errString = strprintf("too many unconfirmed parents [limit: %u]", limits.ancestor_count);
                     return false;
                 }
             }
@@ -260,8 +254,7 @@ bool CTxMemPool::CheckPackageLimits(const Package& package,
     setEntries setAncestors;
     const auto ret = CalculateAncestorsAndCheckLimits(total_size, package.size(),
                                                       setAncestors, staged_ancestors,
-                                                      limitAncestorCount, limitAncestorSize,
-                                                      limitDescendantCount, limitDescendantSize, errString);
+                                                      limits, errString);
     // It's possible to overestimate the ancestor/descendant totals.
     if (!ret) errString.insert(0, "possibly ");
     return ret;
@@ -269,10 +262,7 @@ bool CTxMemPool::CheckPackageLimits(const Package& package,
 
 bool CTxMemPool::CalculateMemPoolAncestors(const CTxMemPoolEntry &entry,
                                            setEntries &setAncestors,
-                                           uint64_t limitAncestorCount,
-                                           uint64_t limitAncestorSize,
-                                           uint64_t limitDescendantCount,
-                                           uint64_t limitDescendantSize,
+                                           const Limits& limits,
                                            std::string &errString,
                                            bool fSearchForParents /* = true */) const
 {
@@ -287,8 +277,8 @@ bool CTxMemPool::CalculateMemPoolAncestors(const CTxMemPoolEntry &entry,
             std::optional<txiter> piter = GetIter(tx.vin[i].prevout.hash);
             if (piter) {
                 staged_ancestors.insert(**piter);
-                if (staged_ancestors.size() + 1 > limitAncestorCount) {
-                    errString = strprintf("too many unconfirmed parents [limit: %u]", limitAncestorCount);
+                if (staged_ancestors.size() + 1 > static_cast<uint64_t>(limits.ancestor_count)) {
+                    errString = strprintf("too many unconfirmed parents [limit: %u]", limits.ancestor_count);
                     return false;
                 }
             }
@@ -302,8 +292,7 @@ bool CTxMemPool::CalculateMemPoolAncestors(const CTxMemPoolEntry &entry,
 
     return CalculateAncestorsAndCheckLimits(entry.GetTxSize(), /*entry_count=*/1,
                                             setAncestors, staged_ancestors,
-                                            limitAncestorCount, limitAncestorSize,
-                                            limitDescendantCount, limitDescendantSize, errString);
+                                            limits, errString);
 }
 
 void CTxMemPool::UpdateAncestorsOf(bool add, txiter it, setEntries &setAncestors)
@@ -347,7 +336,6 @@ void CTxMemPool::UpdateForRemoveFromMempool(const setEntries &entriesToRemove, b
 {
     // For each entry, walk back all ancestors and decrement size associated with this
     // transaction
-    const uint64_t nNoLimit = std::numeric_limits<uint64_t>::max();
     if (updateDescendants) {
         // updateDescendants should be true whenever we're not recursively
         // removing a tx and all its descendants, eg when a transaction is
@@ -390,7 +378,7 @@ void CTxMemPool::UpdateForRemoveFromMempool(const setEntries &entriesToRemove, b
         // mempool parents we'd calculate by searching, and it's important that
         // we use the cached notion of ancestor transactions as the set of
         // things to update for removal.
-        CalculateMemPoolAncestors(entry, setAncestors, nNoLimit, nNoLimit, nNoLimit, nNoLimit, dummy, false);
+        CalculateMemPoolAncestors(entry, setAncestors, Limits::NoLimits(), dummy, false);
         // Note that UpdateAncestorsOf severs the child links that point to
         // removeIt in the entries for the parents of removeIt.
         UpdateAncestorsOf(false, removeIt, setAncestors);
@@ -744,9 +732,8 @@ void CTxMemPool::check(const CCoinsViewCache& active_coins_tip, int64_t spendhei
         assert(std::equal(setParentCheck.begin(), setParentCheck.end(), it->GetMemPoolParentsConst().begin(), comp));
         // Verify ancestor state is correct.
         setEntries setAncestors;
-        uint64_t nNoLimit = std::numeric_limits<uint64_t>::max();
         std::string dummy;
-        CalculateMemPoolAncestors(*it, setAncestors, nNoLimit, nNoLimit, nNoLimit, nNoLimit, dummy);
+        CalculateMemPoolAncestors(*it, setAncestors, Limits::NoLimits(), dummy);
         uint64_t nCountCheck = setAncestors.size() + 1;
         uint64_t nSizeCheck = it->GetTxSize();
         CAmount nFeesCheck = it->GetModifiedFee();
@@ -908,9 +895,8 @@ void CTxMemPool::PrioritiseTransaction(const uint256& hash, const CAmount& nFeeD
             mapTx.modify(it, [&nFeeDelta](CTxMemPoolEntry& e) { e.UpdateModifiedFee(nFeeDelta); });
             // Now update all ancestors' modified fees with descendants
             setEntries setAncestors;
-            uint64_t nNoLimit = std::numeric_limits<uint64_t>::max();
             std::string dummy;
-            CalculateMemPoolAncestors(*it, setAncestors, nNoLimit, nNoLimit, nNoLimit, nNoLimit, dummy, false);
+            CalculateMemPoolAncestors(*it, setAncestors, Limits::NoLimits(), dummy, false);
             for (txiter ancestorIt : setAncestors) {
                 mapTx.modify(ancestorIt, [=](CTxMemPoolEntry& e){ e.UpdateDescendantState(0, nFeeDelta, 0);});
             }
@@ -1049,9 +1035,8 @@ int CTxMemPool::Expire(std::chrono::seconds time)
 void CTxMemPool::addUnchecked(const CTxMemPoolEntry &entry, bool validFeeEstimate)
 {
     setEntries setAncestors;
-    uint64_t nNoLimit = std::numeric_limits<uint64_t>::max();
     std::string dummy;
-    CalculateMemPoolAncestors(entry, setAncestors, nNoLimit, nNoLimit, nNoLimit, nNoLimit, dummy);
+    CalculateMemPoolAncestors(entry, setAncestors, Limits::NoLimits(), dummy);
     return addUnchecked(entry, setAncestors, validFeeEstimate);
 }