[mempool] Persist unbroadcast set to mempool.dat

Ensure that the unbroadcast set will still be meaningful if the node is
restarted.

src/validation.cpp

@@ -4970,6 +4970,7 @@ bool LoadMempool(CTxMemPool& pool)
     int64_t expired = 0;
     int64_t failed = 0;
     int64_t already_there = 0;
+    int64_t unbroadcast = 0;
     int64_t nNow = GetTime();
 
     try {
@@ -5023,12 +5024,21 @@ bool LoadMempool(CTxMemPool& pool)
         for (const auto& i : mapDeltas) {
             pool.PrioritiseTransaction(i.first, i.second);
         }
+
+        std::set<uint256> unbroadcast_txids;
+        file >> unbroadcast_txids;
+        unbroadcast = unbroadcast_txids.size();
+
+        for (const auto& txid : unbroadcast_txids) {
+            pool.AddUnbroadcastTx(txid);
+        }
+
     } catch (const std::exception& e) {
         LogPrintf("Failed to deserialize mempool data on disk: %s. Continuing anyway.\n", e.what());
         return false;
     }
 
-    LogPrintf("Imported mempool transactions from disk: %i succeeded, %i failed, %i expired, %i already there\n", count, failed, expired, already_there);
+    LogPrintf("Imported mempool transactions from disk: %i succeeded, %i failed, %i expired, %i already there, %i waiting for initial broadcast\n", count, failed, expired, already_there, unbroadcast);
     return true;
 }
 
@@ -5038,6 +5048,7 @@ bool DumpMempool(const CTxMemPool& pool)
 
     std::map<uint256, CAmount> mapDeltas;
     std::vector<TxMempoolInfo> vinfo;
+    std::set<uint256> unbroadcast_txids;
 
     static Mutex dump_mutex;
     LOCK(dump_mutex);
@@ -5048,6 +5059,7 @@ bool DumpMempool(const CTxMemPool& pool)
             mapDeltas[i.first] = i.second;
         }
         vinfo = pool.infoAll();
+        unbroadcast_txids = pool.GetUnbroadcastTxs();
     }
 
     int64_t mid = GetTimeMicros();
@@ -5072,6 +5084,10 @@ bool DumpMempool(const CTxMemPool& pool)
         }
 
         file << mapDeltas;
+
+        LogPrintf("Writing %d unbroadcast transactions to disk.\n", unbroadcast_txids.size());
+        file << unbroadcast_txids;
+
         if (!FileCommit(file.Get()))
             throw std::runtime_error("FileCommit failed");
         file.fclose();