Merge bitcoin/bitcoin#27212: test: Make the unlikely race in p2p_invalid_messages impossible

fa1eb0e test: Make the unlikely race in p2p_invalid_messages impossible (MarcoFalke)

Pull request description:

  After `add_p2p_connection` both sides have the verack processed.
  However the pong from conn in reply to the ping from the node has not
  been processed and recorded in totalbytesrecv.
  Flush the pong from conn by sending a ping from conn.

  This should make the unlikely race impossible.

ACKs for top commit:
  mzumsande:
    ACK fa1eb0e
  pinheadmz:
    ACK fa1eb0e

Tree-SHA512: 44166587572e8c0c758cac460fcfd5cf403b2883880128b13dc62e7f74ca5cb8f145bb68a903df177ff0e62faa360f913fd409b009d4cd1360f1f4403ade39ae

Author: fanquake

test/functional/p2p_invalid_messages.py

@@ -80,6 +80,11 @@ def run_test(self):
     def test_buffer(self):
         self.log.info("Test message with header split across two buffers is received")
         conn = self.nodes[0].add_p2p_connection(P2PDataStore())
+        # After add_p2p_connection both sides have the verack processed.
+        # However the pong from conn in reply to the ping from the node has not
+        # been processed and recorded in totalbytesrecv.
+        # Flush the pong from conn by sending a ping from conn.
+        conn.sync_with_ping(timeout=1)
         # Create valid message
         msg = conn.build_message(msg_ping(nonce=12345))
         cut_pos = 12  # Chosen at an arbitrary position within the header
@@ -89,8 +94,6 @@ def test_buffer(self):
         # Wait until node has processed the first half of the message
         self.wait_until(lambda: self.nodes[0].getnettotals()['totalbytesrecv'] != before)
         middle = self.nodes[0].getnettotals()['totalbytesrecv']
-        # If this assert fails, we've hit an unlikely race
-        # where the test framework sent a message in between the two halves
         assert_equal(middle, before + cut_pos)
         conn.send_raw_message(msg[cut_pos:])
         conn.sync_with_ping(timeout=1)