merge bitcoin#22147: p2p: Protect last outbound HB compact block peer

src/net_processing.cpp

@@ -1058,12 +1058,27 @@ void PeerManagerImpl::MaybeSetPeerAsAnnouncingHeaderAndIDs(NodeId nodeid)
         return;
     }
     if (nodestate->fProvidesHeaderAndIDs) {
+        int num_outbound_hb_peers = 0;
         for (std::list<NodeId>::iterator it = lNodesAnnouncingHeaderAndIDs.begin(); it != lNodesAnnouncingHeaderAndIDs.end(); it++) {
             if (*it == nodeid) {
                 lNodesAnnouncingHeaderAndIDs.erase(it);
                 lNodesAnnouncingHeaderAndIDs.push_back(nodeid);
                 return;
             }
+            CNodeState *state = State(*it);
+            if (state != nullptr && !state->m_is_inbound) ++num_outbound_hb_peers;
+        }
+        if (nodestate->m_is_inbound) {
+            // If we're adding an inbound HB peer, make sure we're not removing
+            // our last outbound HB peer in the process.
+            if (lNodesAnnouncingHeaderAndIDs.size() >= 3 && num_outbound_hb_peers == 1) {
+                CNodeState *remove_node = State(lNodesAnnouncingHeaderAndIDs.front());
+                if (remove_node != nullptr && !remove_node->m_is_inbound) {
+                    // Put the HB outbound peer in the second slot, so that it
+                    // doesn't get removed.
+                    std::swap(lNodesAnnouncingHeaderAndIDs.front(), *std::next(lNodesAnnouncingHeaderAndIDs.begin()));
+                }
+            }
         }
         m_connman.ForNode(nodeid, [this](CNode* pfrom){
             LockAssertion lock(::cs_main);

test/functional/p2p_compactblocks_hb.py

@@ -0,0 +1,97 @@
+#!/usr/bin/env python3
+# Copyright (c) 2021 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test compact blocks HB selection logic."""
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import assert_equal
+
+
+class CompactBlocksConnectionTest(BitcoinTestFramework):
+    """Test class for verifying selection of HB peer connections."""
+
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 6
+
+    def peer_info(self, from_node, to_node):
+        """Query from_node for its getpeerinfo about to_node."""
+        for peerinfo in self.nodes[from_node].getpeerinfo():
+            if "(testnode%i)" % to_node in peerinfo['subver']:
+                return peerinfo
+        return None
+
+    def setup_network(self):
+        self.setup_nodes()
+        # Start network with everyone disconnected
+        self.sync_all()
+
+    def relay_block_through(self, peer):
+        """Relay a new block through peer peer, and return HB status between 1 and [2,3,4,5]."""
+        self.connect_nodes(peer, 0)
+        self.nodes[0].generate(1)
+        self.sync_blocks()
+        self.disconnect_nodes(peer, 0)
+        status_to = [self.peer_info(1, i)['bip152_hb_to'] for i in range(2, 6)]
+        status_from = [self.peer_info(i, 1)['bip152_hb_from'] for i in range(2, 6)]
+        assert_equal(status_to, status_from)
+        return status_to
+
+    def run_test(self):
+        self.log.info("Testing reserved high-bandwidth mode slot for outbound peer...")
+
+        # Connect everyone to node 0, and mine some blocks to get all nodes out of IBD.
+        for i in range(1, 6):
+            self.connect_nodes(i, 0)
+        self.nodes[0].generate(2)
+        self.sync_blocks()
+        for i in range(1, 6):
+            self.disconnect_nodes(i, 0)
+
+        # Construct network topology:
+        # - Node 0 is the block producer
+        # - Node 1 is the "target" node being tested
+        # - Nodes 2-5 are intermediaries.
+        #   - Node 1 has an outbound connection to node 2
+        #   - Node 1 has inbound connections from nodes 3-5
+        self.connect_nodes(3, 1)
+        self.connect_nodes(4, 1)
+        self.connect_nodes(5, 1)
+        self.connect_nodes(1, 2)
+
+        # Mine blocks subsequently relaying through nodes 3,4,5 (inbound to node 1)
+        for nodeid in range(3, 6):
+            status = self.relay_block_through(nodeid)
+            assert_equal(status, [False, nodeid >= 3, nodeid >= 4, nodeid >= 5])
+
+        # And again through each. This should not change HB status.
+        for nodeid in range(3, 6):
+            status = self.relay_block_through(nodeid)
+            assert_equal(status, [False, True, True, True])
+
+        # Now relay one block through peer 2 (outbound from node 1), so it should take HB status
+        # from one of the inbounds.
+        status = self.relay_block_through(2)
+        assert_equal(status[0], True)
+        assert_equal(sum(status), 3)
+
+        # Now relay again through nodes 3,4,5. Since 2 is outbound, it should remain HB.
+        for nodeid in range(3, 6):
+            status = self.relay_block_through(nodeid)
+            assert status[0]
+            assert status[nodeid - 2]
+            assert_equal(sum(status), 3)
+
+        # Reconnect peer 2, and retry. Now the three inbounds should be HB again.
+        self.disconnect_nodes(1, 2)
+        self.connect_nodes(1, 2)
+        for nodeid in range(3, 6):
+            status = self.relay_block_through(nodeid)
+            assert not status[0]
+            assert status[nodeid - 2]
+        assert_equal(status, [False, True, True, True])
+
+
+if __name__ == '__main__':
+    CompactBlocksConnectionTest().main()

test/functional/test_runner.py

@@ -194,6 +194,7 @@ BASE_SCRIPTS = [
     'p2p_addrv2_relay.py',
     'wallet_groups.py --legacy-wallet',
     'wallet_groups.py --descriptors',
+    'p2p_compactblocks_hb.py',
     'p2p_disconnect_ban.py',
     'feature_addressindex.py',
     'feature_timestampindex.py',