Merge #16551: test: Test that low difficulty chain fork is rejected

333317c test: Test that low difficulty chain fork is rejected (MarcoFalke)
fa31dc1 test: Pass down correct chain name in tests (MarcoFalke)

Pull request description:

  To prevent OOM, Bitcoin Core will reject chain forks at low difficulty by default. This is the only use-case of checkpoints, so add a test for it to make sure the feature works as expected. If it didn't work, checkpoints would have no use-case and we might as well remove them

ACKs for top commit:
  Sjors:
    Thanks for adding the node 1 example. Code review ACK 333317c

Tree-SHA512: 90dffa540d0904f3cffb61d2382b1a26f84fe9560b7013e4461546383add31a8757b350616a6d43217c59ef7b8b2a1b62bb3bab582c679cbb2c660a782ce7be1

Author: MarcoFalke

test/functional/data/blockheader_testnet3.hex

@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+# Copyright (c) 2019 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 that we reject low difficulty headers to prevent our block tree from filling up with useless bloat"""
+
+from test_framework.messages import (
+    CBlockHeader,
+    FromHex,
+)
+from test_framework.mininode import (
+    P2PInterface,
+    msg_headers,
+)
+from test_framework.test_framework import BitcoinTestFramework
+
+import os
+
+
+class RejectLowDifficultyHeadersTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.chain = 'testnet3'  # Use testnet chain because it has an early checkpoint
+        self.num_nodes = 2
+
+    def add_options(self, parser):
+        parser.add_argument(
+            '--datafile',
+            default='data/blockheader_testnet3.hex',
+            help='Test data file (default: %(default)s)',
+        )
+
+    def run_test(self):
+        self.log.info("Read headers data")
+        self.headers_file_path = os.path.join(os.path.dirname(os.path.realpath(__file__)), self.options.datafile)
+        with open(self.headers_file_path, encoding='utf-8') as headers_data:
+            h_lines = [l.strip() for l in headers_data.readlines()]
+
+        # The headers data is taken from testnet3 for early blocks from genesis until the first checkpoint. There are
+        # two headers with valid POW at height 1 and 2, forking off from genesis. They are indicated by the FORK_PREFIX.
+        FORK_PREFIX = 'fork:'
+        self.headers = [l for l in h_lines if not l.startswith(FORK_PREFIX)]
+        self.headers_fork = [l[len(FORK_PREFIX):] for l in h_lines if l.startswith(FORK_PREFIX)]
+
+        self.headers = [FromHex(CBlockHeader(), h) for h in self.headers]
+        self.headers_fork = [FromHex(CBlockHeader(), h) for h in self.headers_fork]
+
+        self.log.info("Feed all non-fork headers, including and up to the first checkpoint")
+        self.nodes[0].add_p2p_connection(P2PInterface())
+        self.nodes[0].p2p.send_message(msg_headers(self.headers))
+        self.nodes[0].p2p.sync_with_ping()
+        assert {
+            'height': 546,
+            'hash': '000000002a936ca763904c3c35fce2f3556c559c0214345d31b1bcebf76acb70',
+            'branchlen': 546,
+            'status': 'headers-only',
+        } in self.nodes[0].getchaintips()
+
+        self.log.info("Feed all fork headers (fails due to checkpoint)")
+        with self.nodes[0].assert_debug_log(['bad-fork-prior-to-checkpoint (code 67)']):
+            self.nodes[0].p2p.send_message(msg_headers(self.headers_fork))
+            self.nodes[0].p2p.wait_for_disconnect()
+
+        self.log.info("Feed all fork headers (succeeds without checkpoint)")
+        # On node 0 it succeeds because checkpoints are disabled
+        self.restart_node(0, extra_args=['-nocheckpoints'])
+        self.nodes[0].add_p2p_connection(P2PInterface())
+        self.nodes[0].p2p.send_message(msg_headers(self.headers_fork))
+        self.nodes[0].p2p.sync_with_ping()
+        assert {
+            "height": 2,
+            "hash": "00000000b0494bd6c3d5ff79c497cfce40831871cbf39b1bc28bd1dac817dc39",
+            "branchlen": 2,
+            "status": "headers-only",
+        } in self.nodes[0].getchaintips()
+
+        # On node 1 it succeeds because no checkpoint has been reached yet by a chain tip
+        self.nodes[1].add_p2p_connection(P2PInterface())
+        self.nodes[1].p2p.send_message(msg_headers(self.headers_fork))
+        self.nodes[1].p2p.sync_with_ping()
+        assert {
+            "height": 2,
+            "hash": "00000000b0494bd6c3d5ff79c497cfce40831871cbf39b1bc28bd1dac817dc39",
+            "branchlen": 2,
+            "status": "headers-only",
+        } in self.nodes[1].getchaintips()
+
+
+if __name__ == '__main__':
+    RejectLowDifficultyHeadersTest().main()

test/functional/p2p_dos_header_tree.py

@@ -111,7 +111,7 @@ def __init__(self):
     def is_connected(self):
         return self._transport is not None
 
-    def peer_connect(self, dstaddr, dstport, net="regtest"):
+    def peer_connect(self, dstaddr, dstport, *, net):
         assert not self.is_connected
         self.dstaddr = dstaddr
         self.dstport = dstport

test/functional/test_framework/mininode.py

@@ -489,7 +489,7 @@ def add_p2p_connection(self, p2p_conn, *, wait_for_verack=True, **kwargs):
         if 'dstaddr' not in kwargs:
             kwargs['dstaddr'] = '127.0.0.1'
 
-        p2p_conn.peer_connect(**kwargs)()
+        p2p_conn.peer_connect(**kwargs, net=self.chain)()
         self.p2ps.append(p2p_conn)
         if wait_for_verack:
             p2p_conn.wait_for_verack()

test/functional/test_framework/test_node.py

@@ -287,14 +287,22 @@ def initialize_datadir(dirname, n, chain):
     datadir = get_datadir_path(dirname, n)
     if not os.path.isdir(datadir):
         os.makedirs(datadir)
+    # Translate chain name to config name
+    if chain == 'testnet3':
+        chain_name_conf_arg = 'testnet'
+        chain_name_conf_section = 'test'
+    else:
+        chain_name_conf_arg = chain
+        chain_name_conf_section = chain
     with open(os.path.join(datadir, "bitcoin.conf"), 'w', encoding='utf8') as f:
-        f.write("{}=1\n".format(chain))
-        f.write("[{}]\n".format(chain))
+        f.write("{}=1\n".format(chain_name_conf_arg))
+        f.write("[{}]\n".format(chain_name_conf_section))
         f.write("port=" + str(p2p_port(n)) + "\n")
         f.write("rpcport=" + str(rpc_port(n)) + "\n")
         f.write("server=1\n")
         f.write("keypool=1\n")
         f.write("discover=0\n")
+        f.write("dnsseed=0\n")
         f.write("listenonion=0\n")
         f.write("printtoconsole=0\n")
         f.write("upnp=0\n")

test/functional/test_framework/util.py

@@ -197,6 +197,7 @@
     'feature_uacomment.py',
     'wallet_coinbase_category.py',
     'feature_filelock.py',
+    'p2p_dos_header_tree.py',
     'p2p_unrequested_blocks.py',
     'feature_includeconf.py',
     'rpc_deriveaddresses.py',