Merge #18807: [doc / test / mempool] unbroadcast follow-ups

9e1cb1adf1800efe429e348650931f2669b0d2c0 [trivial/doc] Fix comment type (Amiti Uttarwar)
8f30260a67166a6ab7c0f33f7ec1990d3c31761e [doc] Update unbroadcast description in RPC results (Amiti Uttarwar)
750456d6f29c63d57af05bfbdd6035bb9c965de2 [trivial] Remove misleading 'const' (Amiti Uttarwar)
fa32e676e5833a5c5fc735ef00c0a80f5fab7a2c [test] Manage node connections better in mempool persist test (Amiti Uttarwar)
1f94bb0c744a103b633c1051e8fbc01e612097dc [doc] Provide rationale for randomization in scheduling. (Amiti Uttarwar)
9c8a55d9cb0ec73f10b196e79b637aa601c0a6b7 [mempool] Don't throw expected error message when upgrading (Amiti Uttarwar)
ba5498318233ab81decbc585e9619d8ffe2df1b0 [test] Test that wallet transactions aren't rebroadcast before 12 hours (Amiti Uttarwar)
00d44a534b4e5ae249b8011360c6b0f7dc731581 [test] P2P connection behavior should meet expectations (Amiti Uttarwar)
bd093ca15de762fdaf0937a0877d17b0c2bce16e [test] updates to unbroadcast test (Amiti Uttarwar)
dab298d9ab5a5a41685f437db9081fa7b395fa73 [docs] add release notes (Amiti Uttarwar)

Pull request description:

  This PR is a follow up to #18038 which introduced the idea of an unbroadcast set & focuses mostly on documentation updates and test fixes. One small functionality update to not throw an expected error in `LoadMempool` when you upgrade software versions.

  #18895 is another follow up to that addresses other functionality updates.

  Background context:
  The unbroadcast set is a mechanism for the mempool to track locally submitted transactions (via wallet or RPC). The node does a best-effort of delivering the transactions to the network via retries every 10-15 minutes until either a `GETDATA` is received or the transaction is removed from the mempool.

ACKs for top commit:
  MarcoFalke:
    ACK 9e1cb1adf1 👁
  gzhao408:
    ACK [`9e1cb1a`](https://github.com/bitcoin/bitcoin/pull/18807/commits/9e1cb1adf1800efe429e348650931f2669b0d2c0)

Tree-SHA512: 0cd51c4ca368b9dce92d50d73ec6e9df278a259e609eef2858f24cb8595ad07acc3db781d9eb0c351715f18fca5a2b4526838981fdb34a522427e9dc868bdaa6

9 files changed, 68 insertions, 22 deletions

diff --git a/doc/release-notes.md b/doc/release-notes.md
index 0d668a6302..0a2d0fbfc3 100644
--- a/doc/release-notes.md
+++ b/doc/release-notes.md
@@ -65,9 +65,28 @@ Notable changes
 P2P and network changes
 -----------------------
 
+- The mempool now tracks whether transactions submitted via the wallet or RPCs
+  have been successfully broadcast. Every 10-15 minutes, the node will try to
+  announce unbroadcast transactions until a peer requests it via a `getdata`
+  message or the transaction is removed from the mempool for other reasons.
+  The node will not track the broadcast status of transactions submitted to the
+  node using P2P relay. This version reduces the initial broadcast guarantees
+  for wallet transactions submitted via P2P to a node running the wallet. (#18038)
+
 Updated RPCs
 ------------
 
+- `getmempoolinfo` now returns an additional `unbroadcastcount` field. The
+  mempool tracks locally submitted transactions until their initial broadcast
+  is acknowledged by a peer. This field returns the count of transactions
+  waiting for acknowledgement.
+
+- Mempool RPCs such as `getmempoolentry` and `getrawmempool` with
+  `verbose=true` now return an additional `unbroadcast` field. This indicates
+  whether initial broadcast of the transaction has been acknowledged by a
+  peer. `getmempoolancestors` and `getmempooldescendants` are also updated.
+
+
 Changes to Wallet or GUI related RPCs can be found in the GUI or Wallet section below.
 
 New RPCs
@@ -87,6 +106,13 @@ New settings
 Wallet
 ------
 
+- To improve wallet privacy, the frequency of wallet rebroadcast attempts is
+  reduced from approximately once every 15 minutes to once every 12-36 hours.
+  To maintain a similar level of guarantee for initial broadcast of wallet
+  transactions, the mempool tracks these transactions as a part of the newly
+  introduced unbroadcast set. See the "P2P and network changes" section for
+  more information on the unbroadcast set. (#18038)
+
 #### Wallet RPC changes
 
 - The `upgradewallet` RPC replaces the `-upgradewallet` command line option.
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 159036a237..6b9b960552 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -827,7 +827,8 @@ void PeerLogicValidation::ReattemptInitialBroadcast(CScheduler& scheduler) const
         }
     }
 
-    // schedule next run for 10-15 minutes in the future
+    // Schedule next run for 10-15 minutes in the future.
+    // We add randomness on every cycle to avoid the possibility of P2P fingerprinting.
     const std::chrono::milliseconds delta = std::chrono::minutes{10} + GetRandMillis(std::chrono::minutes{5});
     scheduler.scheduleFromNow([&] { ReattemptInitialBroadcast(scheduler); }, delta);
 }
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 4eb47d7b15..b0936cef5a 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -414,7 +414,7 @@ static std::vector<RPCResult> MempoolEntryDescription() { return {
     RPCResult{RPCResult::Type::ARR, "spentby", "unconfirmed transactions spending outputs from this transaction",
         {RPCResult{RPCResult::Type::STR_HEX, "transactionid", "child transaction id"}}},
     RPCResult{RPCResult::Type::BOOL, "bip125-replaceable", "Whether this transaction could be replaced due to BIP125 (replace-by-fee)"},
-    RPCResult{RPCResult::Type::BOOL, "unbroadcast", "Whether this transaction is currently unbroadcast (initial broadcast not yet confirmed)"},
+    RPCResult{RPCResult::Type::BOOL, "unbroadcast", "Whether this transaction is currently unbroadcast (initial broadcast not yet acknowledged by any peers)"},
 };}
 
 static void entryToJSON(const CTxMemPool& pool, UniValue& info, const CTxMemPoolEntry& e) EXCLUSIVE_LOCKS_REQUIRED(pool.cs)
diff --git a/src/txmempool.h b/src/txmempool.h
index 4568eb928d..583f7614b7 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -704,7 +704,7 @@ public:
     /** Adds a transaction to the unbroadcast set */
     void AddUnbroadcastTx(const uint256& txid) {
         LOCK(cs);
-        /** Sanity Check: the transaction should also be in the mempool */
+        // Sanity Check: the transaction should also be in the mempool
         if (exists(txid)) {
             m_unbroadcast_txids.insert(txid);
         }
@@ -714,12 +714,12 @@ public:
     void RemoveUnbroadcastTx(const uint256& txid, const bool unchecked = false);
 
     /** Returns transactions in unbroadcast set */
-    const std::set<uint256> GetUnbroadcastTxs() const {
+    std::set<uint256> GetUnbroadcastTxs() const {
         LOCK(cs);
         return m_unbroadcast_txids;
     }
 
-    // Returns if a txid is in the unbroadcast set
+    /** Returns whether a txid is in the unbroadcast set */
     bool IsUnbroadcastTx(const uint256& txid) const {
         LOCK(cs);
         return (m_unbroadcast_txids.count(txid) != 0);
diff --git a/src/validation.cpp b/src/validation.cpp
index dbdf5028fd..396fc0a1b5 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -5067,12 +5067,18 @@ bool LoadMempool(CTxMemPool& pool)
             pool.PrioritiseTransaction(i.first, i.second);
         }
 
-        std::set<uint256> unbroadcast_txids;
-        file >> unbroadcast_txids;
-        unbroadcast = unbroadcast_txids.size();
+        // TODO: remove this try except in v0.22
+        try {
+          std::set<uint256> unbroadcast_txids;
+          file >> unbroadcast_txids;
+          unbroadcast = unbroadcast_txids.size();
 
-        for (const auto& txid : unbroadcast_txids) {
+          for (const auto& txid : unbroadcast_txids) {
             pool.AddUnbroadcastTx(txid);
+          }
+        } 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.
         }
 
     } catch (const std::exception& e) {
diff --git a/test/functional/mempool_persist.py b/test/functional/mempool_persist.py
index 3969da2eb0..5d00648aed 100755
--- a/test/functional/mempool_persist.py
+++ b/test/functional/mempool_persist.py
@@ -84,7 +84,9 @@ class MempoolPersistTest(BitcoinTestFramework):
         assert_greater_than_or_equal(tx_creation_time_higher, tx_creation_time)
 
         # disconnect nodes & make a txn that remains in the unbroadcast set.
-        disconnect_nodes(self.nodes[0], 2)
+        disconnect_nodes(self.nodes[0], 1)
+        assert(len(self.nodes[0].getpeerinfo()) == 0)
+        assert(len(self.nodes[0].p2ps) == 0)
         self.nodes[0].sendtoaddress(self.nodes[2].getnewaddress(), Decimal("12"))
         connect_nodes(self.nodes[0], 2)
 
@@ -157,8 +159,10 @@ class MempoolPersistTest(BitcoinTestFramework):
         # clear out mempool
         node0.generate(1)
 
-        # disconnect nodes to make a txn that remains in the unbroadcast set.
-        disconnect_nodes(node0, 1)
+        # ensure node0 doesn't have any connections
+        # make a transaction that will remain in the unbroadcast set
+        assert(len(node0.getpeerinfo()) == 0)
+        assert(len(node0.p2ps) == 0)
         node0.sendtoaddress(self.nodes[1].getnewaddress(), Decimal("12"))
 
         # shutdown, then startup with wallet disabled
diff --git a/test/functional/mempool_unbroadcast.py b/test/functional/mempool_unbroadcast.py
index dedf5b8a47..365d011157 100755
--- a/test/functional/mempool_unbroadcast.py
+++ b/test/functional/mempool_unbroadcast.py
@@ -16,6 +16,7 @@ from test_framework.util import (
     disconnect_nodes,
 )
 
+MAX_INITIAL_BROADCAST_DELAY = 15 * 60 # 15 minutes in seconds
 
 class MempoolUnbroadcastTest(BitcoinTestFramework):
     def set_test_params(self):
@@ -72,7 +73,7 @@ class MempoolUnbroadcastTest(BitcoinTestFramework):
         connect_nodes(node, 1)
 
         # fast forward into the future & ensure that the second node has the txns
-        node.mockscheduler(15 * 60)  # 15 min in seconds
+        node.mockscheduler(MAX_INITIAL_BROADCAST_DELAY)
         self.sync_mempools(timeout=30)
         mempool = self.nodes[1].getrawmempool()
         assert rpc_tx_hsh in mempool
@@ -86,15 +87,16 @@ class MempoolUnbroadcastTest(BitcoinTestFramework):
         self.log.info("Add another connection & ensure transactions aren't broadcast again")
 
         conn = node.add_p2p_connection(P2PTxInvStore())
-        node.mockscheduler(15 * 60)
-        time.sleep(5)
+        node.mockscheduler(MAX_INITIAL_BROADCAST_DELAY)
+        time.sleep(2) # allow sufficient time for possibility of broadcast
         assert_equal(len(conn.get_invs()), 0)
 
+        disconnect_nodes(node, 1)
+        node.disconnect_p2ps()
+
     def test_txn_removal(self):
         self.log.info("Test that transactions removed from mempool are removed from unbroadcast set")
         node = self.nodes[0]
-        disconnect_nodes(node, 1)
-        node.disconnect_p2ps
 
         # since the node doesn't have any connections, it will not receive
         # any GETDATAs & thus the transaction will remain in the unbroadcast set.
diff --git a/test/functional/test_framework/mininode.py b/test/functional/test_framework/mininode.py
index d1e982ac3e..337939909e 100755
--- a/test/functional/test_framework/mininode.py
+++ b/test/functional/test_framework/mininode.py
@@ -655,6 +655,8 @@ class P2PTxInvStore(P2PInterface):
                 # save txid
                 self.tx_invs_received[i.hash] += 1
 
+        super().on_inv(message)
+
     def get_invs(self):
         with mininode_lock:
             return list(self.tx_invs_received.keys())
diff --git a/test/functional/wallet_resendwallettransactions.py b/test/functional/wallet_resendwallettransactions.py
index b384998d56..3417616d77 100755
--- a/test/functional/wallet_resendwallettransactions.py
+++ b/test/functional/wallet_resendwallettransactions.py
@@ -49,16 +49,21 @@ class ResendWalletTransactionsTest(BitcoinTestFramework):
         block.solve()
         node.submitblock(ToHex(block))
 
-        # Transaction should not be rebroadcast
         node.syncwithvalidationinterfacequeue()
-        node.p2ps[1].sync_with_ping()
-        assert_equal(node.p2ps[1].tx_invs_received[txid], 0)
+        now = int(time.time())
+
+        # Transaction should not be rebroadcast within first 12 hours
+        # Leave 2 mins for buffer
+        twelve_hrs = 12 * 60 * 60
+        two_min = 2 * 60
+        node.setmocktime(now + twelve_hrs - two_min)
+        time.sleep(2) # ensure enough time has passed for rebroadcast attempt to occur
+        assert_equal(txid in node.p2ps[1].get_invs(), False)
 
         self.log.info("Bump time & check that transaction is rebroadcast")
         # Transaction should be rebroadcast approximately 24 hours in the future,
         # but can range from 12-36. So bump 36 hours to be sure.
-        rebroadcast_time = int(time.time()) + 36 * 60 * 60
-        node.setmocktime(rebroadcast_time)
+        node.setmocktime(now + 36 * 60 * 60)
         wait_until(lambda: node.p2ps[1].tx_invs_received[txid] >= 1, lock=mininode_lock)