test: Check that disconnection happens when wrong garbage terminator is sent

This test type is represented using WRONG_GARBAGE_TERMINATOR.
since the wrong garbage terminator is sent to TestNode, TestNode
will interpret all of the gabage bytes, wrong garbage terminator,
decoy messages and version packet it receives as garbage bytes.

If the length of all these is more than 4095 + 16, it will result
in a missing garbage terminator error. otherwise, it will result
in a V2 handshake timeout error.

Send only MAX_GARBAGE_LEN//2 bytes of garbage data to TestNode
so that the total length received by the TestNode is at max
= (MAX_GARBAGE_LEN//2) + 16 + 10*120 + 20 = 3283 bytes
(which is less than 4095 + 16 bytes) and we get a consistent
V2 handshake timeout error message.

If we do not limit the garbage length sent, we will intermittently
get both missing garbage terminator error and V2 handshake
timeout error based on the garbage length and decoy packets length
which are chosen at random.

Author: stratospher

test/functional/p2p_v2_misbehaving.py

@@ -9,6 +9,7 @@
 from test_framework.messages import MAGIC_BYTES
 from test_framework.p2p import P2PInterface
 from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import random_bitflip
 from test_framework.v2_p2p import (
     EncryptedP2PState,
     MAX_GARBAGE_LEN,
@@ -21,9 +22,11 @@ class TestType(Enum):
     1. EARLY_KEY_RESPONSE - The responder needs to wait until one byte is received which does not match the 16 bytes
     consisting of network magic followed by "version\x00\x00\x00\x00\x00" before sending out its ellswift + garbage bytes
     2. EXCESS_GARBAGE - Disconnection happens when > MAX_GARBAGE_LEN bytes garbage is sent
+    3. WRONG_GARBAGE_TERMINATOR - Disconnection happens when incorrect garbage terminator is sent
     """
     EARLY_KEY_RESPONSE = 0
     EXCESS_GARBAGE = 1
+    WRONG_GARBAGE_TERMINATOR = 2
 
 
 class EarlyKeyResponseState(EncryptedP2PState):
@@ -45,6 +48,19 @@ def generate_keypair_and_garbage(self):
         return super().generate_keypair_and_garbage(garbage_len)
 
 
+class WrongGarbageTerminatorState(EncryptedP2PState):
+    """Add option for sending wrong garbage terminator"""
+    def generate_keypair_and_garbage(self):
+        garbage_len = random.randrange(MAX_GARBAGE_LEN//2)
+        return super().generate_keypair_and_garbage(garbage_len)
+
+    def complete_handshake(self, response):
+        length, handshake_bytes = super().complete_handshake(response)
+        # first 16 bytes returned by complete_handshake() is the garbage terminator
+        wrong_garbage_terminator = random_bitflip(handshake_bytes[:16])
+        return length, wrong_garbage_terminator + handshake_bytes[16:]
+
+
 class MisbehavingV2Peer(P2PInterface):
     """Custom implementation of P2PInterface which uses modified v2 P2P protocol functions for testing purposes."""
     def __init__(self, test_type):
@@ -56,6 +72,8 @@ def connection_made(self, transport):
             self.v2_state = EarlyKeyResponseState(initiating=True, net='regtest')
         elif self.test_type == TestType.EXCESS_GARBAGE:
             self.v2_state = ExcessGarbageState(initiating=True, net='regtest')
+        elif self.test_type == TestType.WRONG_GARBAGE_TERMINATOR:
+            self.v2_state = WrongGarbageTerminatorState(initiating=True, net='regtest')
         super().connection_made(transport)
 
     def data_received(self, t):
@@ -97,6 +115,7 @@ def test_v2disconnection(self):
         expected_debug_message = [
             [],  # EARLY_KEY_RESPONSE
             ["V2 transport error: missing garbage terminator, peer=1"],  # EXCESS_GARBAGE
+            ["V2 handshake timeout peer=2"],  # WRONG_GARBAGE_TERMINATOR
         ]
         for test_type in TestType:
             if test_type == TestType.EARLY_KEY_RESPONSE: