[net processing] [refactor] Move m_next_send_feefilter and m_fee_filter_sent

Move m_next_send_feefilter and m_fee_filter_sent out of the `TxRelay`
data structure. All of the other members of `TxRelay` are related to
sending transactions _to_ the peer, whereas m_fee_filter_sent and
m_next_send_feefilter are both related to receiving transactions _from_
the peer. A node's tx relay behaviour is not always symmetrical (eg a
blocksonly node will ignore incoming transactions, but may still send
out its own transactions), so it doesn't make sense to group the
feefilter sending data with the TxRelay data in a single structure.

This does not change behaviour, since IsBlockOnlyConn() is always equal
to !peer.m_tx_relay. We still don't send feefilter messages to outbound
block-relay-only peers (tested in p2p_feefilter.py).

Author: jnewbery

src/net_processing.cpp

@@ -237,6 +237,13 @@ struct Peer {
 
     /** Whether this peer relays txs via wtxid */
     std::atomic<bool> m_wtxid_relay{false};
+    /** The feerate in the most recent BIP133 `feefilter` message sent to the peer.
+     *  It is *not* a p2p protocol violation for the peer to send us
+     *  transactions with a lower fee rate than this. See BIP133. */
+    CAmount m_fee_filter_sent{0};
+    /** Timestamp after which we will send the next BIP133 `feefilter` message
+      * to the peer. */
+    std::chrono::microseconds m_next_send_feefilter{0};
 
     struct TxRelay {
         mutable RecursiveMutex m_bloom_filter_mutex;
@@ -260,8 +267,6 @@ struct Peer {
 
         /** Minimum fee rate with which to filter inv's to this node */
         std::atomic<CAmount> m_fee_filter_received{0};
-        CAmount m_fee_filter_sent{0};
-        std::chrono::microseconds m_next_send_feefilter{0};
     };
 
     /** Transaction relay data. Will be a nullptr if we're not relaying
@@ -4565,10 +4570,12 @@ void PeerManagerImpl::MaybeSendAddr(CNode& node, Peer& peer, std::chrono::micros
 void PeerManagerImpl::MaybeSendFeefilter(CNode& pto, Peer& peer, std::chrono::microseconds current_time)
 {
     if (m_ignore_incoming_txs) return;
-    if (!peer.m_tx_relay) return;
     if (pto.GetCommonVersion() < FEEFILTER_VERSION) return;
     // peers with the forcerelay permission should not filter txs to us
     if (pto.HasPermission(NetPermissionFlags::ForceRelay)) return;
+    // Don't send feefilter messages to outbound block-relay-only peers since they should never announce
+    // transactions to us, regardless of feefilter state.
+    if (pto.IsBlockOnlyConn()) return;
 
     CAmount currentFilter = m_mempool.GetMinFee(gArgs.GetIntArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000).GetFeePerK();
     static FeeFilterRounder g_filter_rounder{CFeeRate{DEFAULT_MIN_RELAY_TX_FEE}};
@@ -4579,27 +4586,27 @@ void PeerManagerImpl::MaybeSendFeefilter(CNode& pto, Peer& peer, std::chrono::mi
         currentFilter = MAX_MONEY;
     } else {
         static const CAmount MAX_FILTER{g_filter_rounder.round(MAX_MONEY)};
-        if (peer.m_tx_relay->m_fee_filter_sent == MAX_FILTER) {
+        if (peer.m_fee_filter_sent == MAX_FILTER) {
             // Send the current filter if we sent MAX_FILTER previously
             // and made it out of IBD.
-            peer.m_tx_relay->m_next_send_feefilter = 0us;
+            peer.m_next_send_feefilter = 0us;
         }
     }
-    if (current_time > peer.m_tx_relay->m_next_send_feefilter) {
+    if (current_time > peer.m_next_send_feefilter) {
         CAmount filterToSend = g_filter_rounder.round(currentFilter);
         // We always have a fee filter of at least minRelayTxFee
         filterToSend = std::max(filterToSend, ::minRelayTxFee.GetFeePerK());
-        if (filterToSend != peer.m_tx_relay->m_fee_filter_sent) {
+        if (filterToSend != peer.m_fee_filter_sent) {
             m_connman.PushMessage(&pto, CNetMsgMaker(pto.GetCommonVersion()).Make(NetMsgType::FEEFILTER, filterToSend));
-            peer.m_tx_relay->m_fee_filter_sent = filterToSend;
+            peer.m_fee_filter_sent = filterToSend;
         }
-        peer.m_tx_relay->m_next_send_feefilter = GetExponentialRand(current_time, AVG_FEEFILTER_BROADCAST_INTERVAL);
+        peer.m_next_send_feefilter = GetExponentialRand(current_time, AVG_FEEFILTER_BROADCAST_INTERVAL);
     }
     // If the fee filter has changed substantially and it's still more than MAX_FEEFILTER_CHANGE_DELAY
     // until scheduled broadcast, then move the broadcast to within MAX_FEEFILTER_CHANGE_DELAY.
-    else if (current_time + MAX_FEEFILTER_CHANGE_DELAY < peer.m_tx_relay->m_next_send_feefilter &&
-                (currentFilter < 3 * peer.m_tx_relay->m_fee_filter_sent / 4 || currentFilter > 4 * peer.m_tx_relay->m_fee_filter_sent / 3)) {
-        peer.m_tx_relay->m_next_send_feefilter = current_time + GetRandomDuration<std::chrono::microseconds>(MAX_FEEFILTER_CHANGE_DELAY);
+    else if (current_time + MAX_FEEFILTER_CHANGE_DELAY < peer.m_next_send_feefilter &&
+                (currentFilter < 3 * peer.m_fee_filter_sent / 4 || currentFilter > 4 * peer.m_fee_filter_sent / 3)) {
+        peer.m_next_send_feefilter = current_time + GetRandomDuration<std::chrono::microseconds>(MAX_FEEFILTER_CHANGE_DELAY);
     }
 }