Merge bitcoin/bitcoin#29006: test: fix v2 transport intermittent test failure (#29002)

00e0658e77 test: fix v2 transport intermittent test failure (#29002) (Sebastian Falbesoner)

Pull request description:

  This PR improves the following fragile construct for detection of a new connection to the node under test in `p2p_v2_transport.py`:
  6d5790956f/test/functional/p2p_v2_transport.py (L154-L156)
  Only relying on the number of peers for that suffers from race conditions, as unrelated previous peers could disconnect at anytime in-between. In the test run in #29002, the following happens:

  - `getpeerinfo()` is called the first time -> assigned to `num_peers`
  - **previous peer disconnects**, the node's peer count is now `num_peers - 1` (in most test runs, this happens before the first getpeerinfo call)
  - new peer connects, the node's peer count is now `num_peers`
  - the condition that the node's peer count is `num_peers + 1` is never true, test fails

  Use the more robust approach of watching for an increased highest peer id instead (again using the `getpeerinfo` RPC call), with a newly introduced context manager method `TestNode.wait_for_new_peer()`. Note that for the opposite case of a disconnect, no new method is introduced; this is currently used only once in the test and is also simpler.

  Still happy to take suggestions for alternative solutions.

  Fixes #29002.

ACKs for top commit:
  kevkevinpal:
    Concept ACK [00e0658](00e0658e77)
  maflcko:
    Ok, lgtm ACK 00e0658e77
  stratospher:
    ACK 00e0658.

Tree-SHA512: 0118b87f54ea5e6e080ff44f29d6af6674c757a588534b3add040da435f4359e71bf85bc0a5eb7170f99cc9956e1a03c35cce653d642d31eed41bbed1f94f44f

test/functional/p2p_v2_transport.py

@@ -133,9 +133,8 @@ class V2TransportTest(BitcoinTestFramework):
         V1_PREFIX = MAGIC_BYTES["regtest"] + b"version\x00\x00\x00\x00\x00"
         assert_equal(len(V1_PREFIX), 16)
         with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-            num_peers = len(self.nodes[0].getpeerinfo())
-            s.connect(("127.0.0.1", p2p_port(0)))
-            self.wait_until(lambda: len(self.nodes[0].getpeerinfo()) == num_peers + 1)
+            with self.nodes[0].wait_for_new_peer():
+                s.connect(("127.0.0.1", p2p_port(0)))
             s.sendall(V1_PREFIX[:-1])
             assert_equal(self.nodes[0].getpeerinfo()[-1]["transport_protocol_type"], "detecting")
             s.sendall(bytes([V1_PREFIX[-1]]))  # send out last prefix byte
@@ -144,22 +143,23 @@ class V2TransportTest(BitcoinTestFramework):
         # Check wrong network prefix detection (hits if the next 12 bytes correspond to a v1 version message)
         wrong_network_magic_prefix = MAGIC_BYTES["signet"] + V1_PREFIX[4:]
         with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-            s.connect(("127.0.0.1", p2p_port(0)))
+            with self.nodes[0].wait_for_new_peer():
+                s.connect(("127.0.0.1", p2p_port(0)))
             with self.nodes[0].assert_debug_log(["V2 transport error: V1 peer with wrong MessageStart"]):
                 s.sendall(wrong_network_magic_prefix + b"somepayload")
 
         # Check detection of missing garbage terminator (hits after fixed amount of data if terminator never matches garbage)
         MAX_KEY_GARB_AND_GARBTERM_LEN = 64 + 4095 + 16
         with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-            num_peers = len(self.nodes[0].getpeerinfo())
-            s.connect(("127.0.0.1", p2p_port(0)))
-            self.wait_until(lambda: len(self.nodes[0].getpeerinfo()) == num_peers + 1)
+            with self.nodes[0].wait_for_new_peer():
+                s.connect(("127.0.0.1", p2p_port(0)))
             s.sendall(b'\x00' * (MAX_KEY_GARB_AND_GARBTERM_LEN - 1))
             self.wait_until(lambda: self.nodes[0].getpeerinfo()[-1]["bytesrecv"] == MAX_KEY_GARB_AND_GARBTERM_LEN - 1)
             with self.nodes[0].assert_debug_log(["V2 transport error: missing garbage terminator"]):
+                peer_id = self.nodes[0].getpeerinfo()[-1]["id"]
                 s.sendall(b'\x00')  # send out last byte
                 # should disconnect immediately
-                self.wait_until(lambda: len(self.nodes[0].getpeerinfo()) == num_peers)
+                self.wait_until(lambda: not peer_id in [p["id"] for p in self.nodes[0].getpeerinfo()])
 
 
 if __name__ == '__main__':

test/functional/test_framework/test_node.py

@@ -519,6 +519,24 @@ class TestNode():
             'Expected messages "{}" does not partially match log:\n\n{}\n\n'.format(
                 str(expected_msgs), print_log))
 
+    @contextlib.contextmanager
+    def wait_for_new_peer(self, timeout=5):
+        """
+        Wait until the node is connected to at least one new peer. We detect this
+        by watching for an increased highest peer id, using the `getpeerinfo` RPC call.
+        Note that the simpler approach of only accounting for the number of peers
+        suffers from race conditions, as disconnects from unrelated previous peers
+        could happen anytime in-between.
+        """
+        def get_highest_peer_id():
+            peer_info = self.getpeerinfo()
+            return peer_info[-1]["id"] if peer_info else -1
+
+        initial_peer_id = get_highest_peer_id()
+        yield
+        wait_until_helper_internal(lambda: get_highest_peer_id() > initial_peer_id,
+                                   timeout=timeout, timeout_factor=self.timeout_factor)
+
     @contextlib.contextmanager
     def profile_with_perf(self, profile_name: str):
         """