test: p2p: check that headers message with invalid proof-of-work disconnects peer #26184

The node doesn't have any blocks, so you are getting the genesis block, which can't be send over p2p anyway, as the previous block is unknown.

received header ......: missing prev block 0000000000000000000000000000000000000000000000000000000000000000

Yeah, in fact, since the PoW check is the first one that actually inspects headers data, the content of the block header doesn't matter at all for this test-case; could even be completely random bytes:

diff --git a/test/functional/p2p_invalid_messages.py b/test/functional/p2p_invalid_messages.py
index f5fe590c62..e85dc00082 100755
--- a/test/functional/p2p_invalid_messages.py
+++ b/test/functional/p2p_invalid_messages.py
@@ -29,6 +29,7 @@ from test_framework.p2p import (
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
+    random_bytes,
 )

 VALID_DATA_LIMIT = MAX_PROTOCOL_MESSAGE_LENGTH - 5  # Account for the 5-byte length prefix
@@ -252,8 +253,7 @@ class InvalidMessagesTest(BitcoinTestFramework):

     def test_invalid_pow_headers_msg(self):
         self.log.info("Test headers message with invalid proof-of-work is logged as misbehaving and disconnects peer")
-        blockheader_tip = self.nodes[0].getblockheader(self.nodes[0].getbestblockhash(), False)
-        blockheader_invalid_pow = from_hex(CBlockHeader(), blockheader_tip)
+        blockheader_invalid_pow = from_hex(CBlockHeader(), random_bytes(80).hex())
         blockheader_invalid_pow.rehash()
         while not blockheader_invalid_pow.hash.startswith('f'):
             blockheader_invalid_pow.nNonce += 1

But I agree that the test-case in its current form suggest that header would be valid with correct PoW. Will take a deeper look in a bit.

Do we need to create a new peer here (bad_peer)? Couldn't we use the same used before? e.g.:

diff --git a/test/functional/p2p_invalid_messages.py b/test/functional/p2p_invalid_messages.py
index 7c6777759..39505c115 100755
--- a/test/functional/p2p_invalid_messages.py
+++ b/test/functional/p2p_invalid_messages.py
@@ -265,18 +265,17 @@ class InvalidMessagesTest(BitcoinTestFramework):
         while not blockheader.hash.startswith('0'):
             blockheader.nNonce += 1
             blockheader.rehash()
-        good_peer = self.nodes[0].add_p2p_connection(P2PInterface())
-        good_peer.send_and_ping(msg_headers([blockheader]))
+        peer = self.nodes[0].add_p2p_connection(P2PInterface())
+        peer.send_and_ping(msg_headers([blockheader]))
         assert_equal(self.nodes[0].getblockchaininfo()['headers'], 1)
 
         # invalidate PoW
         while not blockheader.hash.startswith('f'):
             blockheader.nNonce += 1
             blockheader.rehash()
-        bad_peer = self.nodes[0].add_p2p_connection(P2PInterface())
         with self.nodes[0].assert_debug_log(['Misbehaving', 'header with invalid proof of work']):
-            bad_peer.send_message(msg_headers([blockheader]))
-            bad_peer.wait_for_disconnect()
+            peer.send_message(msg_headers([blockheader]))
+            peer.wait_for_disconnect()

Good point, done.

nit: Could also check the connected header hash

assert any(x["hash"] == blockheader.hash and x["status"] == "headers-only" for x in self.nodes[0].getchaintips())

Good idea, done. Decided to access the getchaintips() result at index 0 (works since the result is always returned in decreasing order of height) in order to take use of assert_equal, so if this ever fails, we see the expected/actual values immediately.