[wallet] Schedule tx rebroadcasts in wallet

Removes the now-unused Broadcast/ResendWalletTransactions interface from
validationinterface.

The wallet_resendwallettransactions.py needs a sleep added at the start
to make sure that the rebroadcast scheduler is warmed up before the next
block is mined.

src/interfaces/chain.cpp

@@ -207,16 +207,6 @@ public:
         m_notifications->UpdatedBlockTip();
     }
     void ChainStateFlushed(const CBlockLocator& locator) override { m_notifications->ChainStateFlushed(locator); }
-    void ResendWalletTransactions(CConnman*) override
-    {
-        // `cs_main` is always held when this method is called, so it is safe to
-        // call `assumeLocked`. This is awkward, and the `assumeLocked` method
-        // should be able to be removed entirely if `ResendWalletTransactions`
-        // is replaced by a wallet timer as suggested in
-        // https://github.com/bitcoin/bitcoin/issues/15619
-        auto locked_chain = m_chain.assumeLocked();
-        m_notifications->ResendWalletTransactions(*locked_chain);
-    }
     Chain& m_chain;
     Chain::Notifications* m_notifications;
 };
@@ -351,6 +341,7 @@ public:
     CAmount maxTxFee() override { return ::maxTxFee; }
     bool getPruneMode() override { return ::fPruneMode; }
     bool p2pEnabled() override { return g_connman != nullptr; }
+    bool isReadyToBroadcast() override { return !::fImporting && !::fReindex && !IsInitialBlockDownload(); }
     bool isInitialBlockDownload() override { return IsInitialBlockDownload(); }
     bool shutdownRequested() override { return ShutdownRequested(); }
     int64_t getAdjustedTime() override { return GetAdjustedTime(); }

src/interfaces/chain.h

@@ -223,6 +223,9 @@ public:
     //! Check if p2p enabled.
     virtual bool p2pEnabled() = 0;
 
+    //! Check if the node is ready to broadcast transactions.
+    virtual bool isReadyToBroadcast() = 0;
+
     //! Check if in IBD.
     virtual bool isInitialBlockDownload() = 0;
 
@@ -258,7 +261,6 @@ public:
         virtual void BlockDisconnected(const CBlock& block) {}
         virtual void UpdatedBlockTip() {}
         virtual void ChainStateFlushed(const CBlockLocator& locator) {}
-        virtual void ResendWalletTransactions(Lock& locked_chain) {}
     };
 
     //! Register handler for notifications.

src/net_processing.cpp

@@ -3546,14 +3546,6 @@ bool PeerLogicValidation::SendMessages(CNode* pto)
             }
         }
 
-        // Resend wallet transactions that haven't gotten in a block yet
-        // Except during reindex, importing and IBD, when old wallet
-        // transactions become unconfirmed and spams other nodes.
-        if (!fReindex && !fImporting && !IsInitialBlockDownload())
-        {
-            GetMainSignals().Broadcast(connman);
-        }
-
         //
         // Try sending block announcements via headers
         //

src/validationinterface.cpp

@@ -25,7 +25,6 @@ struct ValidationInterfaceConnections {
     boost::signals2::scoped_connection BlockDisconnected;
     boost::signals2::scoped_connection TransactionRemovedFromMempool;
     boost::signals2::scoped_connection ChainStateFlushed;
-    boost::signals2::scoped_connection Broadcast;
     boost::signals2::scoped_connection BlockChecked;
     boost::signals2::scoped_connection NewPoWValidBlock;
 };
@@ -37,7 +36,6 @@ struct MainSignalsInstance {
     boost::signals2::signal<void (const std::shared_ptr<const CBlock> &)> BlockDisconnected;
     boost::signals2::signal<void (const CTransactionRef &)> TransactionRemovedFromMempool;
     boost::signals2::signal<void (const CBlockLocator &)> ChainStateFlushed;
-    boost::signals2::signal<void (CConnman* connman)> Broadcast;
     boost::signals2::signal<void (const CBlock&, const CValidationState&)> BlockChecked;
     boost::signals2::signal<void (const CBlockIndex *, const std::shared_ptr<const CBlock>&)> NewPoWValidBlock;
 
@@ -101,7 +99,6 @@ void RegisterValidationInterface(CValidationInterface* pwalletIn) {
     conns.BlockDisconnected = g_signals.m_internals->BlockDisconnected.connect(std::bind(&CValidationInterface::BlockDisconnected, pwalletIn, std::placeholders::_1));
     conns.TransactionRemovedFromMempool = g_signals.m_internals->TransactionRemovedFromMempool.connect(std::bind(&CValidationInterface::TransactionRemovedFromMempool, pwalletIn, std::placeholders::_1));
     conns.ChainStateFlushed = g_signals.m_internals->ChainStateFlushed.connect(std::bind(&CValidationInterface::ChainStateFlushed, pwalletIn, std::placeholders::_1));
-    conns.Broadcast = g_signals.m_internals->Broadcast.connect(std::bind(&CValidationInterface::ResendWalletTransactions, pwalletIn, std::placeholders::_1));
     conns.BlockChecked = g_signals.m_internals->BlockChecked.connect(std::bind(&CValidationInterface::BlockChecked, pwalletIn, std::placeholders::_1, std::placeholders::_2));
     conns.NewPoWValidBlock = g_signals.m_internals->NewPoWValidBlock.connect(std::bind(&CValidationInterface::NewPoWValidBlock, pwalletIn, std::placeholders::_1, std::placeholders::_2));
 }
@@ -175,10 +172,6 @@ void CMainSignals::ChainStateFlushed(const CBlockLocator &locator) {
     });
 }
 
-void CMainSignals::Broadcast(CConnman* connman) {
-    m_internals->Broadcast(connman);
-}
-
 void CMainSignals::BlockChecked(const CBlock& block, const CValidationState& state) {
     m_internals->BlockChecked(block, state);
 }

src/validationinterface.h

@@ -134,8 +134,6 @@ protected:
      * Called on a background thread.
      */
     virtual void ChainStateFlushed(const CBlockLocator &locator) {}
-    /** Tells listeners to broadcast their data. */
-    virtual void ResendWalletTransactions(CConnman* connman) {}
     /**
      * Notifies listeners of a block validation result.
      * If the provided CValidationState IsValid, the provided block
@@ -184,7 +182,6 @@ public:
     void BlockConnected(const std::shared_ptr<const CBlock> &, const CBlockIndex *pindex, const std::shared_ptr<const std::vector<CTransactionRef>> &);
     void BlockDisconnected(const std::shared_ptr<const CBlock> &);
     void ChainStateFlushed(const CBlockLocator &);
-    void Broadcast(CConnman* connman);
     void BlockChecked(const CBlock&, const CValidationState&);
     void NewPoWValidBlock(const CBlockIndex *, const std::shared_ptr<const CBlock>&);
 };

src/wallet/init.cpp

@@ -211,8 +211,9 @@ void StartWallets(CScheduler& scheduler)
         pwallet->postInitProcess();
     }
 
-    // Run a thread to flush wallet periodically
+    // Schedule periodic wallet flushes and tx rebroadcasts
     scheduler.scheduleEvery(MaybeCompactWalletDB, 500);
+    scheduler.scheduleEvery(MaybeResendWalletTxs, 1000);
 }
 
 void FlushWallets()

src/wallet/wallet.cpp

@@ -2114,8 +2114,21 @@ bool CWalletTx::IsEquivalentTo(const CWalletTx& _tx) const
         return CTransaction(tx1) == CTransaction(tx2);
 }
 
+// Rebroadcast transactions from the wallet. We do this on a random timer
+// to slightly obfuscate which transactions come from our wallet.
+//
+// Ideally, we'd only resend transactions that we think should have been
+// mined in the most recent block. Any transaction that wasn't in the top
+// blockweight of transactions in the mempool shouldn't have been mined,
+// and so is probably just sitting in the mempool waiting to be confirmed.
+// Rebroadcasting does nothing to speed up confirmation and only damages
+// privacy.
 void CWallet::ResendWalletTransactions(interfaces::Chain::Lock& locked_chain)
 {
+    // During reindex, importing and IBD, old wallet transactions become
+    // unconfirmed. Don't resend them as that would spam other nodes.
+    if (!chain().isReadyToBroadcast()) return;
+
     // Do this infrequently and randomly to avoid giving away
     // that these are our transactions.
     if (GetTime() < nNextResend || !fBroadcastTransactions) return;
@@ -2149,7 +2162,13 @@ void CWallet::ResendWalletTransactions(interfaces::Chain::Lock& locked_chain)
 
 /** @} */ // end of mapWallet
 
-
+void MaybeResendWalletTxs()
+{
+    for (const std::shared_ptr<CWallet>& pwallet : GetWallets()) {
+        auto locked_chain = pwallet->chain().lock();
+        pwallet->ResendWalletTransactions(*locked_chain);
+    }
+}
 
 
 /** @defgroup Actions

src/wallet/wallet.h

@@ -949,7 +949,7 @@ public:
     ScanResult ScanForWalletTransactions(const uint256& first_block, const uint256& last_block, const WalletRescanReserver& reserver, bool fUpdate);
     void TransactionRemovedFromMempool(const CTransactionRef &ptx) override;
     void ReacceptWalletTransactions(interfaces::Chain::Lock& locked_chain) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
-    void ResendWalletTransactions(interfaces::Chain::Lock& locked_chain) override;
+    void ResendWalletTransactions(interfaces::Chain::Lock& locked_chain);
     struct Balance {
         CAmount m_mine_trusted{0};           //!< Trusted, at depth=GetBalance.min_depth or more
         CAmount m_mine_untrusted_pending{0}; //!< Untrusted, but in mempool (pending)
@@ -1232,6 +1232,12 @@ public:
     friend struct WalletTestingSetup;
 };
 
+/**
+ * Called periodically by the schedule thread. Prompts individual wallets to resend
+ * their transactions. Actual rebroadcast schedule is managed by the wallets themselves.
+ */
+void MaybeResendWalletTxs();
+
 /** A key allocated from the key pool. */
 class CReserveKey final : public CReserveScript
 {

test/functional/wallet_resendwallettransactions.py

@@ -39,6 +39,12 @@ class ResendWalletTransactionsTest(BitcoinTestFramework):
         self.log.info("Create a new transaction and wait until it's broadcast")
         txid = int(node.sendtoaddress(node.getnewaddress(), 1), 16)
 
+        # Wallet rebroadcast is first scheduled 1 sec after startup (see
+        # nNextResend in ResendWalletTransactions()). Sleep for just over a
+        # second to be certain that it has been called before the first
+        # setmocktime call below.
+        time.sleep(1.1)
+
         # Can take a few seconds due to transaction trickling
         wait_until(lambda: node.p2p.tx_invs_received[txid] >= 1, lock=mininode_lock)