[mempool] Revert unbroadcast set to tracking just txid

When I originally implemented the unbroadcast set in 18038, it just tracked
txids. After 18038 was merged, I offered a patch to 18044 to make the
unbroadcast changes compatible with wtxid relay. In this patch, I updated
`unbroadcast_txids` to a map of txid -> wtxid. Post merge review comments shed
light on the fact that this update was unnecessary, and distracting. So, this
commit updates the unbroadcast ids back to a set.

src/net_processing.cpp

@@ -889,15 +889,16 @@ void PeerLogicValidation::InitializeNode(CNode *pnode) {
 
 void PeerLogicValidation::ReattemptInitialBroadcast(CScheduler& scheduler) const
 {
-    std::map<uint256, uint256> unbroadcast_txids = m_mempool.GetUnbroadcastTxs();
+    std::set<uint256> unbroadcast_txids = m_mempool.GetUnbroadcastTxs();
 
-    for (const auto& elem : unbroadcast_txids) {
-        // Sanity check: all unbroadcast txns should exist in the mempool
-        if (m_mempool.exists(elem.first)) {
+    for (const auto& txid : unbroadcast_txids) {
+        CTransactionRef tx = m_mempool.get(txid);
+
+        if (tx != nullptr) {
             LOCK(cs_main);
-            RelayTransaction(elem.first, elem.second, m_connman);
+            RelayTransaction(txid, tx->GetWitnessHash(), m_connman);
         } else {
-            m_mempool.RemoveUnbroadcastTx(elem.first, true);
+            m_mempool.RemoveUnbroadcastTx(txid, true);
         }
     }
 

src/node/transaction.cpp

@@ -80,7 +80,7 @@ TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef t
     if (relay) {
         // the mempool tracks locally submitted transactions to make a
         // best-effort of initial broadcast
-        node.mempool->AddUnbroadcastTx(hashTx, tx->GetWitnessHash());
+        node.mempool->AddUnbroadcastTx(hashTx);
 
         LOCK(cs_main);
         RelayTransaction(hashTx, tx->GetWitnessHash(), *node.connman);

src/txmempool.h

@@ -574,10 +574,9 @@ class CTxMemPool
     std::vector<indexed_transaction_set::const_iterator> GetSortedDepthAndScore() const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
     /**
-     * track locally submitted transactions to periodically retry initial broadcast
-     * map of txid -> wtxid
+     * Track locally submitted transactions to periodically retry initial broadcast.
      */
-    std::map<uint256, uint256> m_unbroadcast_txids GUARDED_BY(cs);
+    std::set<uint256> m_unbroadcast_txids GUARDED_BY(cs);
 
 public:
     indirectmap<COutPoint, const CTransaction*> mapNextTx GUARDED_BY(cs);
@@ -739,19 +738,20 @@ class CTxMemPool
     size_t DynamicMemoryUsage() const;
 
     /** Adds a transaction to the unbroadcast set */
-    void AddUnbroadcastTx(const uint256& txid, const uint256& wtxid) {
+    void AddUnbroadcastTx(const uint256& txid)
+    {
         LOCK(cs);
-        // Sanity Check: the transaction should also be in the mempool
-        if (exists(txid)) {
-            m_unbroadcast_txids[txid] = wtxid;
-        }
-    }
+        // Sanity check the transaction is in the mempool & insert into
+        // unbroadcast set.
+        if (exists(txid)) m_unbroadcast_txids.insert(txid);
+    };
 
     /** Removes a transaction from the unbroadcast set */
     void RemoveUnbroadcastTx(const uint256& txid, const bool unchecked = false);
 
     /** Returns transactions in unbroadcast set */
-    std::map<uint256, uint256> GetUnbroadcastTxs() const {
+    std::set<uint256> GetUnbroadcastTxs() const
+    {
         LOCK(cs);
         return m_unbroadcast_txids;
     }

src/validation.cpp

@@ -5116,21 +5116,18 @@ bool LoadMempool(CTxMemPool& pool)
         }
 
         // TODO: remove this try except in v0.22
-        std::map<uint256, uint256> unbroadcast_txids;
+        std::set<uint256> unbroadcast_txids;
         try {
           file >> unbroadcast_txids;
           unbroadcast = unbroadcast_txids.size();
         } catch (const std::exception&) {
           // mempool.dat files created prior to v0.21 will not have an
           // unbroadcast set. No need to log a failure if parsing fails here.
         }
-        for (const auto& elem : unbroadcast_txids) {
-            // Don't add unbroadcast transactions that didn't get back into the
-            // mempool.
-            const CTransactionRef& added_tx = pool.get(elem.first);
-            if (added_tx != nullptr) {
-                pool.AddUnbroadcastTx(elem.first, added_tx->GetWitnessHash());
-            }
+        for (const auto& txid : unbroadcast_txids) {
+            // Ensure transactions were accepted to mempool then add to
+            // unbroadcast set.
+            if (pool.get(txid) != nullptr) pool.AddUnbroadcastTx(txid);
         }
     } catch (const std::exception& e) {
         LogPrintf("Failed to deserialize mempool data on disk: %s. Continuing anyway.\n", e.what());
@@ -5147,7 +5144,7 @@ bool DumpMempool(const CTxMemPool& pool)
 
     std::map<uint256, CAmount> mapDeltas;
     std::vector<TxMempoolInfo> vinfo;
-    std::map<uint256, uint256> unbroadcast_txids;
+    std::set<uint256> unbroadcast_txids;
 
     static Mutex dump_mutex;
     LOCK(dump_mutex);