Unified iterating through txset history entries (#4655)

# Description

Resolves #4567.

# Checklist
- [ ] Reviewed the
[contributing](https://github.com/stellar/stellar-core/blob/master/CONTRIBUTING.md#submitting-changes)
document
- [ ] Rebased on top of master (no merge commits)
- [ ] Ran `clang-format` v8.0.0 (via `make format` or the Visual Studio
extension)
- [ ] Compiles
- [ ] Ran all tests
- [ ] If change impacts performance, include supporting evidence per the
[performance
document](https://github.com/stellar/stellar-core/blob/master/performance-eval/performance-eval.md)

Author: marta-lokhova

src/catchup/ApplyCheckpointWork.cpp

@@ -8,6 +8,7 @@
 #include "catchup/ApplyLedgerWork.h"
 #include "history/FileTransferInfo.h"
 #include "history/HistoryManager.h"
+#include "history/HistoryUtils.h"
 #include "historywork/Progress.h"
 #include "ledger/CheckpointRange.h"
 #include "ledger/LedgerManager.h"
@@ -139,36 +140,22 @@ ApplyCheckpointWork::getCurrentTxSet()
     auto& lm = mApp.getLedgerManager();
     auto seq = lm.getLastClosedLedgerNum() + 1;
 
-    // Check mTxHistoryEntry prior to loading next history entry.
-    // This order is important because it accounts for ledger "gaps"
-    // in the history archives (which are caused by ledgers with empty tx
-    // sets, as those are not uploaded).
-    do
+    auto foundEntry = getHistoryEntryForLedger<TransactionHistoryEntry>(
+        mTxIn, mTxHistoryEntry, seq);
+
+    if (foundEntry)
     {
-        if (mTxHistoryEntry.ledgerSeq < seq)
-        {
-            CLOG_DEBUG(History, "Skipping txset for ledger {}",
-                       mTxHistoryEntry.ledgerSeq);
-        }
-        else if (mTxHistoryEntry.ledgerSeq > seq)
+        CLOG_DEBUG(History, "Loaded txset for ledger {}", seq);
+        if (mTxHistoryEntry.ext.v() == 0)
         {
-            break;
+            return TxSetXDRFrame::makeFromWire(mTxHistoryEntry.txSet);
         }
         else
         {
-            releaseAssert(mTxHistoryEntry.ledgerSeq == seq);
-            CLOG_DEBUG(History, "Loaded txset for ledger {}", seq);
-            if (mTxHistoryEntry.ext.v() == 0)
-            {
-                return TxSetXDRFrame::makeFromWire(mTxHistoryEntry.txSet);
-            }
-            else
-            {
-                return TxSetXDRFrame::makeFromWire(
-                    mTxHistoryEntry.ext.generalizedTxSet());
-            }
+            return TxSetXDRFrame::makeFromWire(
+                mTxHistoryEntry.ext.generalizedTxSet());
         }
-    } while (mTxIn && mTxIn.readOne(mTxHistoryEntry));
+    }
 
     CLOG_DEBUG(History, "Using empty txset for ledger {}", seq);
     return TxSetXDRFrame::makeEmpty(lm.getLastClosedLedgerHeader());
@@ -181,29 +168,18 @@ ApplyCheckpointWork::getCurrentTxResultSet()
     ZoneScoped;
     auto& lm = mApp.getLedgerManager();
     auto seq = lm.getLastClosedLedgerNum() + 1;
-    // Check mTxResultSet prior to loading next result set.
-    // This order is important because it accounts for ledger "gaps"
-    // in the history archives (which are caused by ledgers with empty tx
-    // sets, as those are not uploaded).
-    while (mTxResultIn && mTxResultIn->readOne(*mTxHistoryResultEntry))
+    releaseAssertOrThrow(mTxHistoryResultEntry);
+
+    if (mTxResultIn)
     {
-        if (mTxHistoryResultEntry)
+        auto foundEntry =
+            getHistoryEntryForLedger<TransactionHistoryResultEntry>(
+                *mTxResultIn, *mTxHistoryResultEntry, seq);
+
+        if (foundEntry)
         {
-            if (mTxHistoryResultEntry->ledgerSeq < seq)
-            {
-                CLOG_DEBUG(History, "Advancing past txresultset for ledger {}",
-                           mTxHistoryResultEntry->ledgerSeq);
-            }
-            else if (mTxHistoryResultEntry->ledgerSeq > seq)
-            {
-                break;
-            }
-            else
-            {
-                releaseAssert(mTxHistoryResultEntry->ledgerSeq == seq);
-                CLOG_DEBUG(History, "Loaded txresultset for ledger {}", seq);
-                return std::make_optional(mTxHistoryResultEntry->txResultSet);
-            }
+            CLOG_DEBUG(History, "Loaded txresultset for ledger {}", seq);
+            return std::make_optional(mTxHistoryResultEntry->txResultSet);
         }
     }
     CLOG_DEBUG(History, "No txresultset for ledger {}", seq);

src/history/HistoryUtils.cpp

@@ -0,0 +1,60 @@
+// Copyright 2025 Stellar Development Foundation and contributors. Licensed
+// under the Apache License, Version 2.0. See the COPYING file at the root
+// of this distribution or at http://www.apache.org/licenses/LICENSE-2.0
+
+#include "history/HistoryUtils.h"
+#include "util/Logging.h"
+#include "util/XDRStream.h"
+#include "xdr/Stellar-ledger.h"
+#include <Tracy.hpp>
+
+namespace stellar
+{
+
+template <typename T>
+bool
+getHistoryEntryForLedger(XDRInputFileStream& stream, T& currentEntry,
+                         uint32_t targetLedger,
+                         std::function<void(uint32_t ledgerSeq)> validateFn)
+{
+    ZoneScoped;
+
+    auto readNextWithValidation = [&]() {
+        auto res = stream.readOne(currentEntry);
+        if (res && validateFn)
+        {
+            validateFn(currentEntry.ledgerSeq);
+        }
+        return res;
+    };
+
+    do
+    {
+        if (currentEntry.ledgerSeq < targetLedger)
+        {
+            CLOG_DEBUG(History, "Advancing past txhistory entry for ledger {}",
+                       currentEntry.ledgerSeq);
+        }
+        else if (currentEntry.ledgerSeq > targetLedger)
+        {
+            // No entry for this ledger
+            break;
+        }
+        else
+        {
+            // Found the entry for our target ledger
+            return true;
+        }
+    } while (stream && readNextWithValidation());
+
+    return false;
+}
+
+template bool getHistoryEntryForLedger<TransactionHistoryEntry>(
+    XDRInputFileStream& stream, TransactionHistoryEntry& currentEntry,
+    uint32_t targetLedger, std::function<void(uint32_t ledgerSeq)> validateFn);
+
+template bool getHistoryEntryForLedger<TransactionHistoryResultEntry>(
+    XDRInputFileStream& stream, TransactionHistoryResultEntry& currentEntry,
+    uint32_t targetLedger, std::function<void(uint32_t ledgerSeq)> validateFn);
+}

src/history/HistoryUtils.h

@@ -0,0 +1,26 @@
+// Copyright 2025 Stellar Development Foundation and contributors. Licensed
+// under the Apache License, Version 2.0. See the COPYING file at the root
+// of this distribution or at http://www.apache.org/licenses/LICENSE-2.0
+
+#pragma once
+
+#include <cstdint>
+#include <functional>
+
+namespace stellar
+{
+
+class XDRInputFileStream;
+
+// This function centralizes the logic for iterating through
+// history archive tx set entries (TransactionHistoryEntry,
+// TransactionHistoryResultEntry) that may have gaps. Reads an entry from the
+// stream into currentEntry until eof or an entry is found with ledgerSeq >=
+// targetLedger. Returns true if targetLedger found (currentEntry will be set to
+// the target ledger). Otherwise returns false, where currentEntry is the last
+// entry read from the stream.
+template <typename T>
+bool getHistoryEntryForLedger(
+    XDRInputFileStream& stream, T& currentEntry, uint32_t targetLedger,
+    std::function<void(uint32_t ledgerSeq)> validateFn = nullptr);
+}

src/historywork/VerifyTxResultsWork.cpp

@@ -4,6 +4,7 @@
 
 #include "historywork/VerifyTxResultsWork.h"
 #include "history/FileTransferInfo.h"
+#include "history/HistoryUtils.h"
 #include "ledger/LedgerManager.h"
 #include "main/ErrorMessages.h"
 #include "util/FileSystemException.h"
@@ -144,47 +145,30 @@ VerifyTxResultsWork::getCurrentTxResultSet(uint32_t ledger)
     TransactionHistoryResultEntry trs;
     trs.ledgerSeq = ledger;
 
-    auto readNextWithValidation = [&]() {
-        auto res = mResIn.readOne(mTxResultEntry);
-        if (res)
+    auto validateFn = [this](uint32_t readLedger) {
+        auto low = HistoryManager::firstLedgerInCheckpointContaining(
+            mCheckpoint, mApp.getConfig());
+        if (readLedger > mCheckpoint || readLedger < low)
         {
-            auto readLedger = mTxResultEntry.ledgerSeq;
-            auto low = HistoryManager::firstLedgerInCheckpointContaining(
-                mCheckpoint, mApp.getConfig());
-            if (readLedger > mCheckpoint || readLedger < low)
-            {
-                throw std::runtime_error("Results outside of checkpoint range");
-            }
+            throw std::runtime_error("Results outside of checkpoint range");
+        }
 
-            if (readLedger <= mLastSeenLedger)
-            {
-                throw std::runtime_error("Malformed or duplicate results: "
-                                         "ledgers must be strictly increasing");
-            }
-            mLastSeenLedger = readLedger;
+        if (readLedger <= mLastSeenLedger)
+        {
+            throw std::runtime_error("Malformed or duplicate results: "
+                                     "ledgers must be strictly increasing");
         }
-        return res;
+        mLastSeenLedger = readLedger;
     };
 
-    do
+    auto foundEntry = getHistoryEntryForLedger<TransactionHistoryResultEntry>(
+        mResIn, mTxResultEntry, ledger, validateFn);
+
+    if (foundEntry)
     {
-        if (mTxResultEntry.ledgerSeq < ledger)
-        {
-            CLOG_DEBUG(History, "Processed tx results for ledger {}",
-                       mTxResultEntry.ledgerSeq);
-        }
-        else if (mTxResultEntry.ledgerSeq > ledger)
-        {
-            // No tx results in this ledger
-            break;
-        }
-        else
-        {
-            CLOG_DEBUG(History, "Loaded tx result set for ledger {}", ledger);
-            trs.txResultSet = mTxResultEntry.txResultSet;
-            return trs;
-        }
-    } while (mResIn && readNextWithValidation());
+        CLOG_DEBUG(History, "Loaded tx result set for ledger {}", ledger);
+        trs.txResultSet = mTxResultEntry.txResultSet;
+    }
 
     return trs;
 }