Add functional test for block announcements during initial headers sync

Author: sdaftuar

test/functional/p2p_initial_headers_sync.py

@@ -0,0 +1,105 @@
+#!/usr/bin/env python3
+# Copyright (c) 2022 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 initial headers download
+
+Test that we only try to initially sync headers from one peer (until our chain
+is close to caught up), and that each block announcement results in only one
+additional peer receiving a getheaders message.
+"""
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.messages import (
+    CInv,
+    MSG_BLOCK,
+    msg_headers,
+    msg_inv,
+)
+from test_framework.p2p import (
+    p2p_lock,
+    P2PInterface,
+)
+from test_framework.util import (
+    assert_equal,
+)
+import random
+
+class HeadersSyncTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 1
+
+    def announce_random_block(self, peers):
+        new_block_announcement = msg_inv(inv=[CInv(MSG_BLOCK, random.randrange(1<<256))])
+        for p in peers:
+            p.send_and_ping(new_block_announcement)
+
+    def run_test(self):
+        self.log.info("Adding a peer to node0")
+        peer1 = self.nodes[0].add_p2p_connection(P2PInterface())
+
+        # Wait for peer1 to receive a getheaders
+        peer1.wait_for_getheaders()
+        # An empty reply will clear the outstanding getheaders request,
+        # allowing additional getheaders requests to be sent to this peer in
+        # the future.
+        peer1.send_message(msg_headers())
+
+        self.log.info("Connecting two more peers to node0")
+        # Connect 2 more peers; they should not receive a getheaders yet
+        peer2 = self.nodes[0].add_p2p_connection(P2PInterface())
+        peer3 = self.nodes[0].add_p2p_connection(P2PInterface())
+
+        all_peers = [peer1, peer2, peer3]
+
+        self.log.info("Verify that peer2 and peer3 don't receive a getheaders after connecting")
+        for p in all_peers:
+            p.sync_with_ping()
+        with p2p_lock:
+            assert "getheaders" not in peer2.last_message
+            assert "getheaders" not in peer3.last_message
+
+        with p2p_lock:
+            peer1.last_message.pop("getheaders", None)
+
+        self.log.info("Have all peers announce a new block")
+        self.announce_random_block(all_peers)
+
+        self.log.info("Check that peer1 receives a getheaders in response")
+        peer1.wait_for_getheaders()
+        peer1.send_message(msg_headers()) # Send empty response, see above
+        with p2p_lock:
+            peer1.last_message.pop("getheaders", None)
+
+        self.log.info("Check that exactly 1 of {peer2, peer3} received a getheaders in response")
+        count = 0
+        peer_receiving_getheaders = None
+        for p in [peer2, peer3]:
+            with p2p_lock:
+                if "getheaders" in p.last_message:
+                    count += 1
+                    peer_receiving_getheaders = p
+                    p.last_message.pop("getheaders", None)
+                    p.send_message(msg_headers()) # Send empty response, see above
+
+        assert_equal(count, 1)
+
+        self.log.info("Announce another new block, from all peers")
+        self.announce_random_block(all_peers)
+
+        self.log.info("Check that peer1 receives a getheaders in response")
+        peer1.wait_for_getheaders()
+
+        self.log.info("Check that the remaining peer received a getheaders as well")
+        expected_peer = peer2
+        if peer2 == peer_receiving_getheaders:
+            expected_peer = peer3
+
+        expected_peer.wait_for_getheaders()
+
+        self.log.info("Success!")
+
+if __name__ == '__main__':
+    HeadersSyncTest().main()
+

test/functional/test_runner.py

@@ -246,6 +246,7 @@
     'rpc_generate.py',
     'wallet_balance.py --legacy-wallet',
     'wallet_balance.py --descriptors',
+    'p2p_initial_headers_sync.py',
     'feature_nulldummy.py',
     'mempool_accept.py',
     'mempool_expiry.py',