txorphanage: Extract GetOrphanTx

Summary:
Extract orphan lookup code into GetOrphanTx function.

This is a backport of [[bitcoin/bitcoin#21148 | core#21148]] [6/14]
bitcoin/bitcoin@f294da7

Depends on D11485

Test Plan: `ninja all check-all`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11486

src/net_processing.cpp

@@ -2991,14 +2991,12 @@ void PeerManagerImpl::ProcessOrphanTx(const Config &config,
         const TxId orphanTxId = *orphan_work_set.begin();
         orphan_work_set.erase(orphan_work_set.begin());
 
-        auto orphan_it = mapOrphanTransactions.find(orphanTxId);
-        if (orphan_it == mapOrphanTransactions.end()) {
+        const auto [porphanTx, from_peer] = GetOrphanTx(orphanTxId);
+        if (porphanTx == nullptr) {
             continue;
         }
 
-        const CTransactionRef porphanTx = orphan_it->second.tx;
         TxValidationState state;
-
         if (AcceptToMemoryPool(::ChainstateActive(), config, m_mempool, state,
                                porphanTx, false /* bypass_limits */)) {
             LogPrint(BCLog::MEMPOOL, "   accepted orphan tx %s\n",
@@ -3011,10 +3009,9 @@ void PeerManagerImpl::ProcessOrphanTx(const Config &config,
             if (state.IsInvalid()) {
                 LogPrint(BCLog::MEMPOOL,
                          "   invalid orphan tx %s from peer=%d. %s\n",
-                         orphanTxId.ToString(), orphan_it->second.fromPeer,
-                         state.ToString());
+                         orphanTxId.ToString(), from_peer, state.ToString());
                 // Punish peer that gave us an invalid orphan tx
-                MaybePunishNodeForTx(orphan_it->second.fromPeer, state);
+                MaybePunishNodeForTx(from_peer, state);
             }
             // Has inputs but not accepted to mempool
             // Probably non-standard or insufficient fee

src/txorphanage.cpp

@@ -131,3 +131,13 @@ bool HaveOrphanTx(const TxId &txid) {
     LOCK(g_cs_orphans);
     return mapOrphanTransactions.count(txid);
 }
+
+std::pair<CTransactionRef, NodeId> GetOrphanTx(const TxId &txid) {
+    AssertLockHeld(g_cs_orphans);
+
+    const auto it = mapOrphanTransactions.find(txid);
+    if (it == mapOrphanTransactions.end()) {
+        return {nullptr, -1};
+    }
+    return {it->second.tx, it->second.fromPeer};
+}

src/txorphanage.h

@@ -31,6 +31,8 @@ void AddChildrenToWorkSet(const CTransaction &tx,
                           std::set<TxId> &orphan_work_set)
     EXCLUSIVE_LOCKS_REQUIRED(g_cs_orphans);
 bool HaveOrphanTx(const TxId &txid) LOCKS_EXCLUDED(g_cs_orphans);
+std::pair<CTransactionRef, NodeId> GetOrphanTx(const TxId &txid)
+    EXCLUSIVE_LOCKS_REQUIRED(g_cs_orphans);
 
 /**
  * Map from txid to orphan transaction record. Limited by