Merge #11707: [tests] Fix sendheaders

9d42cc333 [tests] address review comments (John Newbery)
f0c4ab9a7 [tests] fix flakiness in sendheaders.py (John Newbery)
25fd6e2c2 [tests] refactor check_last_announcement() in sendheaders.py (John Newbery)
f39d4bbd1 [tests] tidy up BaseNode in sendheaders.py (John Newbery)
2613c545f [tests] fix flake8 warnings in sendheaders.py (John Newbery)

Pull request description:

  This PR should fix the intermittent failure of sendheaders.py described in #11673. The first three commits are tidying up and refactoring the file. The final commit _fix flakiness in sendheaders.py_ fixes the intermittent failures. The commit message for that commit describes the problems that are being fixed.

  I think @laanwj @MeshCollider @MarcoFalke have seen these failures.

  fixes #11673

Tree-SHA512: 278e1af85f2eae00f970f2d8ef33686dd52b4f62180dea4cfdaff7bcf3287c6f1c2930355d99461a12f0c51c4d42cc3b1cb3275174134028ca4d06ffc24c18dd

1 files changed, 141 insertions, 121 deletions

diff --git a/test/functional/sendheaders.py b/test/functional/sendheaders.py
index 55bb80ea00..68c0d95b4f 100755
--- a/test/functional/sendheaders.py
+++ b/test/functional/sendheaders.py
@@ -4,11 +4,13 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test behavior of headers messages to announce blocks.
 
-Setup: 
+Setup:
 
-- Two nodes, two p2p connections to node0. One p2p connection should only ever
-  receive inv's (omitted from testing description below, this is our control).
-  Second node is used for creating reorgs.
+- Two nodes:
+    - node0 is the node-under-test. We create two p2p connections to it. The
+      first p2p connection is a control and should only ever receive inv's. The
+      second p2p connection tests the headers sending logic.
+    - node1 is used to create reorgs.
 
 test_null_locators
 ==================
@@ -83,35 +85,45 @@ d. Announce 49 headers that don't connect.
 e. Announce one more that doesn't connect.
    Expect: disconnect.
 """
-
-from test_framework.mininode import *
-from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import *
 from test_framework.blocktools import create_block, create_coinbase
+from test_framework.mininode import (
+    CBlockHeader,
+    CInv,
+    NODE_WITNESS,
+    NetworkThread,
+    NodeConnCB,
+    mininode_lock,
+    msg_block,
+    msg_getblocks,
+    msg_getdata,
+    msg_getheaders,
+    msg_headers,
+    msg_inv,
+    msg_sendheaders,
+)
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+    sync_blocks,
+    wait_until,
+)
 
+DIRECT_FETCH_RESPONSE_TIME = 0.05
 
-direct_fetch_response_time = 0.05
-
-class TestNode(NodeConnCB):
+class BaseNode(NodeConnCB):
     def __init__(self):
         super().__init__()
         self.block_announced = False
         self.last_blockhash_announced = None
 
-    def clear_last_announcement(self):
-        with mininode_lock:
-            self.block_announced = False
-            self.last_message.pop("inv", None)
-            self.last_message.pop("headers", None)
-
-    # Request data for a list of block hashes
-    def get_data(self, block_hashes):
+    def send_get_data(self, block_hashes):
+        """Request data for a list of block hashes."""
         msg = msg_getdata()
         for x in block_hashes:
             msg.inv.append(CInv(2, x))
         self.connection.send_message(msg)
 
-    def get_headers(self, locator, hashstop):
+    def send_get_headers(self, locator, hashstop):
         msg = msg_getheaders()
         msg.locator.vHave = locator
         msg.hashstop = hashstop
@@ -122,6 +134,27 @@ class TestNode(NodeConnCB):
         msg.inv = [CInv(2, blockhash)]
         self.connection.send_message(msg)
 
+    def send_header_for_blocks(self, new_blocks):
+        headers_message = msg_headers()
+        headers_message.headers = [CBlockHeader(b) for b in new_blocks]
+        self.send_message(headers_message)
+
+    def send_getblocks(self, locator):
+        getblocks_message = msg_getblocks()
+        getblocks_message.locator.vHave = locator
+        self.send_message(getblocks_message)
+
+    def wait_for_getdata(self, hash_list, timeout=60):
+        if hash_list == []:
+            return
+
+        test_function = lambda: "getdata" in self.last_message and [x.hash for x in self.last_message["getdata"].inv] == hash_list
+        wait_until(test_function, timeout=timeout, lock=mininode_lock)
+
+    def wait_for_block_announcement(self, block_hash, timeout=60):
+        test_function = lambda: self.last_blockhash_announced == block_hash
+        wait_until(test_function, timeout=timeout, lock=mininode_lock)
+
     def on_inv(self, conn, message):
         self.block_announced = True
         self.last_blockhash_announced = message.inv[-1].hash
@@ -132,97 +165,79 @@ class TestNode(NodeConnCB):
             message.headers[-1].calc_sha256()
             self.last_blockhash_announced = message.headers[-1].sha256
 
-    # Test whether the last announcement we received had the
-    # right header or the right inv
-    # inv and headers should be lists of block hashes
+    def clear_last_announcement(self):
+        with mininode_lock:
+            self.block_announced = False
+            self.last_message.pop("inv", None)
+            self.last_message.pop("headers", None)
+
     def check_last_announcement(self, headers=None, inv=None):
-        expect_headers = headers if headers != None else []
-        expect_inv = inv if inv != None else []
+        """Test whether the last announcement received had the right header or the right inv.
+
+        inv and headers should be lists of block hashes."""
+
         test_function = lambda: self.block_announced
         wait_until(test_function, timeout=60, lock=mininode_lock)
+
         with mininode_lock:
             self.block_announced = False
 
-            success = True
             compare_inv = []
             if "inv" in self.last_message:
                 compare_inv = [x.hash for x in self.last_message["inv"].inv]
-            if compare_inv != expect_inv:
-                success = False
+            if inv is not None:
+                assert_equal(compare_inv, inv)
 
-            hash_headers = []
+            compare_headers = []
             if "headers" in self.last_message:
-                # treat headers as a list of block hashes
-                hash_headers = [ x.sha256 for x in self.last_message["headers"].headers ]
-            if hash_headers != expect_headers:
-                success = False
+                compare_headers = [x.sha256 for x in self.last_message["headers"].headers]
+            if headers is not None:
+                assert_equal(compare_headers, headers)
 
             self.last_message.pop("inv", None)
             self.last_message.pop("headers", None)
-        return success
-
-    def wait_for_getdata(self, hash_list, timeout=60):
-        if hash_list == []:
-            return
-
-        test_function = lambda: "getdata" in self.last_message and [x.hash for x in self.last_message["getdata"].inv] == hash_list
-        wait_until(test_function, timeout=timeout, lock=mininode_lock)
-        return
-
-    def wait_for_block_announcement(self, block_hash, timeout=60):
-        test_function = lambda: self.last_blockhash_announced == block_hash
-        wait_until(test_function, timeout=timeout, lock=mininode_lock)
-        return
-
-    def send_header_for_blocks(self, new_blocks):
-        headers_message = msg_headers()
-        headers_message.headers = [ CBlockHeader(b) for b in new_blocks ]
-        self.send_message(headers_message)
-
-    def send_getblocks(self, locator):
-        getblocks_message = msg_getblocks()
-        getblocks_message.locator.vHave = locator
-        self.send_message(getblocks_message)
 
 class SendHeadersTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
         self.num_nodes = 2
 
-    # mine count blocks and return the new tip
     def mine_blocks(self, count):
+        """Mine count blocks and return the new tip."""
+
         # Clear out last block announcement from each p2p listener
         [x.clear_last_announcement() for x in self.nodes[0].p2ps]
         self.nodes[0].generate(count)
         return int(self.nodes[0].getbestblockhash(), 16)
 
-    # mine a reorg that invalidates length blocks (replacing them with
-    # length+1 blocks).
-    # Note: we clear the state of our p2p connections after the
-    # to-be-reorged-out blocks are mined, so that we don't break later tests.
-    # return the list of block hashes newly mined
     def mine_reorg(self, length):
-        self.nodes[0].generate(length) # make sure all invalidated blocks are node0's
+        """Mine a reorg that invalidates length blocks (replacing them with # length+1 blocks).
+
+        Note: we clear the state of our p2p connections after the
+        to-be-reorged-out blocks are mined, so that we don't break later tests.
+        return the list of block hashes newly mined."""
+
+        self.nodes[0].generate(length)  # make sure all invalidated blocks are node0's
         sync_blocks(self.nodes, wait=0.1)
         for x in self.nodes[0].p2ps:
             x.wait_for_block_announcement(int(self.nodes[0].getbestblockhash(), 16))
             x.clear_last_announcement()
 
         tip_height = self.nodes[1].getblockcount()
-        hash_to_invalidate = self.nodes[1].getblockhash(tip_height-(length-1))
+        hash_to_invalidate = self.nodes[1].getblockhash(tip_height - (length - 1))
         self.nodes[1].invalidateblock(hash_to_invalidate)
-        all_hashes = self.nodes[1].generate(length+1) # Must be longer than the orig chain
+        all_hashes = self.nodes[1].generate(length + 1)  # Must be longer than the orig chain
         sync_blocks(self.nodes, wait=0.1)
         return [int(x, 16) for x in all_hashes]
 
     def run_test(self):
         # Setup the p2p connections and start up the network thread.
-        inv_node = self.nodes[0].add_p2p_connection(TestNode())
-        # Set nServices to 0 for test_node, so no block download will occur outside of
-        # direct fetching
-        test_node = self.nodes[0].add_p2p_connection(TestNode(), services=NODE_WITNESS)
+        inv_node = self.nodes[0].add_p2p_connection(BaseNode())
+        # Make sure NODE_NETWORK is not set for test_node, so no block download
+        # will occur outside of direct fetching
+        test_node = self.nodes[0].add_p2p_connection(BaseNode(), services=NODE_WITNESS)
 
-        NetworkThread().start() # Start up network handling in another thread
+        NetworkThread().start()  # Start up network handling in another thread
 
         # Test logic begins here
         inv_node.wait_for_verack()
@@ -232,27 +247,32 @@ class SendHeadersTest(BitcoinTestFramework):
         inv_node.sync_with_ping()
         test_node.sync_with_ping()
 
-        self.test_null_locators(test_node)
+        self.test_null_locators(test_node, inv_node)
         self.test_nonnull_locators(test_node, inv_node)
 
-    def test_null_locators(self, test_node):
+    def test_null_locators(self, test_node, inv_node):
         tip = self.nodes[0].getblockheader(self.nodes[0].generate(1)[0])
         tip_hash = int(tip["hash"], 16)
 
+        inv_node.check_last_announcement(inv=[tip_hash], headers=[])
+        test_node.check_last_announcement(inv=[tip_hash], headers=[])
+
         self.log.info("Verify getheaders with null locator and valid hashstop returns headers.")
         test_node.clear_last_announcement()
-        test_node.get_headers(locator=[], hashstop=tip_hash)
-        assert_equal(test_node.check_last_announcement(headers=[tip_hash]), True)
+        test_node.send_get_headers(locator=[], hashstop=tip_hash)
+        test_node.check_last_announcement(headers=[tip_hash])
 
         self.log.info("Verify getheaders with null locator and invalid hashstop does not return headers.")
         block = create_block(int(tip["hash"], 16), create_coinbase(tip["height"] + 1), tip["mediantime"] + 1)
         block.solve()
         test_node.send_header_for_blocks([block])
         test_node.clear_last_announcement()
-        test_node.get_headers(locator=[], hashstop=int(block.hash, 16))
+        test_node.send_get_headers(locator=[], hashstop=int(block.hash, 16))
         test_node.sync_with_ping()
         assert_equal(test_node.block_announced, False)
+        inv_node.clear_last_announcement()
         test_node.send_message(msg_block(block))
+        inv_node.check_last_announcement(inv=[int(block.hash, 16)], headers=[])
 
     def test_nonnull_locators(self, test_node, inv_node):
         tip = int(self.nodes[0].getbestblockhash(), 16)
@@ -263,30 +283,30 @@ class SendHeadersTest(BitcoinTestFramework):
         for i in range(4):
             old_tip = tip
             tip = self.mine_blocks(1)
-            assert_equal(inv_node.check_last_announcement(inv=[tip]), True)
-            assert_equal(test_node.check_last_announcement(inv=[tip]), True)
+            inv_node.check_last_announcement(inv=[tip], headers=[])
+            test_node.check_last_announcement(inv=[tip], headers=[])
             # Try a few different responses; none should affect next announcement
             if i == 0:
                 # first request the block
-                test_node.get_data([tip])
+                test_node.send_get_data([tip])
                 test_node.wait_for_block(tip)
             elif i == 1:
                 # next try requesting header and block
-                test_node.get_headers(locator=[old_tip], hashstop=tip)
-                test_node.get_data([tip])
+                test_node.send_get_headers(locator=[old_tip], hashstop=tip)
+                test_node.send_get_data([tip])
                 test_node.wait_for_block(tip)
-                test_node.clear_last_announcement() # since we requested headers...
+                test_node.clear_last_announcement()  # since we requested headers...
             elif i == 2:
                 # this time announce own block via headers
                 height = self.nodes[0].getblockcount()
                 last_time = self.nodes[0].getblock(self.nodes[0].getbestblockhash())['time']
                 block_time = last_time + 1
-                new_block = create_block(tip, create_coinbase(height+1), block_time)
+                new_block = create_block(tip, create_coinbase(height + 1), block_time)
                 new_block.solve()
                 test_node.send_header_for_blocks([new_block])
                 test_node.wait_for_getdata([new_block.sha256])
                 test_node.send_message(msg_block(new_block))
-                test_node.sync_with_ping() # make sure this block is processed
+                test_node.sync_with_ping()  # make sure this block is processed
                 inv_node.clear_last_announcement()
                 test_node.clear_last_announcement()
 
@@ -297,15 +317,15 @@ class SendHeadersTest(BitcoinTestFramework):
         # commence and keep working.
         test_node.send_message(msg_sendheaders())
         prev_tip = int(self.nodes[0].getbestblockhash(), 16)
-        test_node.get_headers(locator=[prev_tip], hashstop=0)
+        test_node.send_get_headers(locator=[prev_tip], hashstop=0)
         test_node.sync_with_ping()
 
         # Now that we've synced headers, headers announcements should work
         tip = self.mine_blocks(1)
-        assert_equal(inv_node.check_last_announcement(inv=[tip]), True)
-        assert_equal(test_node.check_last_announcement(headers=[tip]), True)
+        inv_node.check_last_announcement(inv=[tip], headers=[])
+        test_node.check_last_announcement(headers=[tip])
 
-        height = self.nodes[0].getblockcount()+1
+        height = self.nodes[0].getblockcount() + 1
         block_time += 10  # Advance far enough ahead
         for i in range(10):
             # Mine i blocks, and alternate announcing either via
@@ -314,7 +334,7 @@ class SendHeadersTest(BitcoinTestFramework):
             # with block header, even though the blocks are never requested
             for j in range(2):
                 blocks = []
-                for b in range(i+1):
+                for b in range(i + 1):
                     blocks.append(create_block(tip, create_coinbase(height), block_time))
                     blocks[-1].solve()
                     tip = blocks[-1].sha256
@@ -328,7 +348,7 @@ class SendHeadersTest(BitcoinTestFramework):
                     test_node.send_header_for_blocks(blocks)
                     # Test that duplicate inv's won't result in duplicate
                     # getdata requests, or duplicate headers announcements
-                    [ inv_node.send_block_inv(x.sha256) for x in blocks ]
+                    [inv_node.send_block_inv(x.sha256) for x in blocks]
                     test_node.wait_for_getdata([x.sha256 for x in blocks])
                     inv_node.sync_with_ping()
                 else:
@@ -339,7 +359,7 @@ class SendHeadersTest(BitcoinTestFramework):
                     # getdata requests (the check is further down)
                     inv_node.send_header_for_blocks(blocks)
                     inv_node.sync_with_ping()
-                [ test_node.send_message(msg_block(x)) for x in blocks ]
+                [test_node.send_message(msg_block(x)) for x in blocks]
                 test_node.sync_with_ping()
                 inv_node.sync_with_ping()
                 # This block should not be announced to the inv node (since it also
@@ -347,8 +367,8 @@ class SendHeadersTest(BitcoinTestFramework):
                 assert "inv" not in inv_node.last_message
                 assert "headers" not in inv_node.last_message
                 tip = self.mine_blocks(1)
-                assert_equal(inv_node.check_last_announcement(inv=[tip]), True)
-                assert_equal(test_node.check_last_announcement(headers=[tip]), True)
+                inv_node.check_last_announcement(inv=[tip], headers=[])
+                test_node.check_last_announcement(headers=[tip])
                 height += 1
                 block_time += 1
 
@@ -362,16 +382,16 @@ class SendHeadersTest(BitcoinTestFramework):
             # First try mining a reorg that can propagate with header announcement
             new_block_hashes = self.mine_reorg(length=7)
             tip = new_block_hashes[-1]
-            assert_equal(inv_node.check_last_announcement(inv=[tip]), True)
-            assert_equal(test_node.check_last_announcement(headers=new_block_hashes), True)
+            inv_node.check_last_announcement(inv=[tip], headers=[])
+            test_node.check_last_announcement(headers=new_block_hashes)
 
-            block_time += 8 
+            block_time += 8
 
             # Mine a too-large reorg, which should be announced with a single inv
             new_block_hashes = self.mine_reorg(length=8)
             tip = new_block_hashes[-1]
-            assert_equal(inv_node.check_last_announcement(inv=[tip]), True)
-            assert_equal(test_node.check_last_announcement(inv=[tip]), True)
+            inv_node.check_last_announcement(inv=[tip], headers=[])
+            test_node.check_last_announcement(inv=[tip], headers=[])
 
             block_time += 9
 
@@ -379,42 +399,42 @@ class SendHeadersTest(BitcoinTestFramework):
             fork_point = int(fork_point, 16)
 
             # Use getblocks/getdata
-            test_node.send_getblocks(locator = [fork_point])
-            assert_equal(test_node.check_last_announcement(inv=new_block_hashes), True)
-            test_node.get_data(new_block_hashes)
+            test_node.send_getblocks(locator=[fork_point])
+            test_node.check_last_announcement(inv=new_block_hashes, headers=[])
+            test_node.send_get_data(new_block_hashes)
             test_node.wait_for_block(new_block_hashes[-1])
 
             for i in range(3):
                 # Mine another block, still should get only an inv
                 tip = self.mine_blocks(1)
-                assert_equal(inv_node.check_last_announcement(inv=[tip]), True)
-                assert_equal(test_node.check_last_announcement(inv=[tip]), True)
+                inv_node.check_last_announcement(inv=[tip], headers=[])
+                test_node.check_last_announcement(inv=[tip], headers=[])
                 if i == 0:
                     # Just get the data -- shouldn't cause headers announcements to resume
-                    test_node.get_data([tip])
+                    test_node.send_get_data([tip])
                     test_node.wait_for_block(tip)
                 elif i == 1:
                     # Send a getheaders message that shouldn't trigger headers announcements
                     # to resume (best header sent will be too old)
-                    test_node.get_headers(locator=[fork_point], hashstop=new_block_hashes[1])
-                    test_node.get_data([tip])
+                    test_node.send_get_headers(locator=[fork_point], hashstop=new_block_hashes[1])
+                    test_node.send_get_data([tip])
                     test_node.wait_for_block(tip)
                 elif i == 2:
-                    test_node.get_data([tip])
+                    test_node.send_get_data([tip])
                     test_node.wait_for_block(tip)
                     # This time, try sending either a getheaders to trigger resumption
-                    # of headers announcements, or mine a new block and inv it, also 
+                    # of headers announcements, or mine a new block and inv it, also
                     # triggering resumption of headers announcements.
                     if j == 0:
-                        test_node.get_headers(locator=[tip], hashstop=0)
+                        test_node.send_get_headers(locator=[tip], hashstop=0)
                         test_node.sync_with_ping()
                     else:
                         test_node.send_block_inv(tip)
                         test_node.sync_with_ping()
             # New blocks should now be announced with header
             tip = self.mine_blocks(1)
-            assert_equal(inv_node.check_last_announcement(inv=[tip]), True)
-            assert_equal(test_node.check_last_announcement(headers=[tip]), True)
+            inv_node.check_last_announcement(inv=[tip], headers=[])
+            test_node.check_last_announcement(headers=[tip])
 
         self.log.info("Part 3: success!")
 
@@ -434,7 +454,7 @@ class SendHeadersTest(BitcoinTestFramework):
             height += 1
             inv_node.send_message(msg_block(blocks[-1]))
 
-        inv_node.sync_with_ping() # Make sure blocks are processed
+        inv_node.sync_with_ping()  # Make sure blocks are processed
         test_node.last_message.pop("getdata", None)
         test_node.send_header_for_blocks(blocks)
         test_node.sync_with_ping()
@@ -453,9 +473,9 @@ class SendHeadersTest(BitcoinTestFramework):
 
         test_node.send_header_for_blocks(blocks)
         test_node.sync_with_ping()
-        test_node.wait_for_getdata([x.sha256 for x in blocks], timeout=direct_fetch_response_time)
+        test_node.wait_for_getdata([x.sha256 for x in blocks], timeout=DIRECT_FETCH_RESPONSE_TIME)
 
-        [ test_node.send_message(msg_block(x)) for x in blocks ]
+        [test_node.send_message(msg_block(x)) for x in blocks]
 
         test_node.sync_with_ping()
 
@@ -484,13 +504,13 @@ class SendHeadersTest(BitcoinTestFramework):
         # both blocks (same work as tip)
         test_node.send_header_for_blocks(blocks[1:2])
         test_node.sync_with_ping()
-        test_node.wait_for_getdata([x.sha256 for x in blocks[0:2]], timeout=direct_fetch_response_time)
+        test_node.wait_for_getdata([x.sha256 for x in blocks[0:2]], timeout=DIRECT_FETCH_RESPONSE_TIME)
 
         # Announcing 16 more headers should trigger direct fetch for 14 more
         # blocks
         test_node.send_header_for_blocks(blocks[2:18])
         test_node.sync_with_ping()
-        test_node.wait_for_getdata([x.sha256 for x in blocks[2:16]], timeout=direct_fetch_response_time)
+        test_node.wait_for_getdata([x.sha256 for x in blocks[2:16]], timeout=DIRECT_FETCH_RESPONSE_TIME)
 
         # Announcing 1 more header should not trigger any response
         test_node.last_message.pop("getdata", None)
@@ -502,7 +522,7 @@ class SendHeadersTest(BitcoinTestFramework):
         self.log.info("Part 4: success!")
 
         # Now deliver all those blocks we announced.
-        [ test_node.send_message(msg_block(x)) for x in blocks ]
+        [test_node.send_message(msg_block(x)) for x in blocks]
 
         self.log.info("Part 5: Testing handling of unconnecting headers")
         # First we test that receipt of an unconnecting header doesn't prevent
@@ -524,7 +544,7 @@ class SendHeadersTest(BitcoinTestFramework):
             test_node.wait_for_getheaders()
             test_node.send_header_for_blocks(blocks)
             test_node.wait_for_getdata([x.sha256 for x in blocks])
-            [ test_node.send_message(msg_block(x)) for x in blocks ]
+            [test_node.send_message(msg_block(x)) for x in blocks]
             test_node.sync_with_ping()
             assert_equal(int(self.nodes[0].getbestblockhash(), 16), blocks[1].sha256)
 
@@ -532,7 +552,7 @@ class SendHeadersTest(BitcoinTestFramework):
         # Now we test that if we repeatedly don't send connecting headers, we
         # don't go into an infinite loop trying to get them to connect.
         MAX_UNCONNECTING_HEADERS = 10
-        for j in range(MAX_UNCONNECTING_HEADERS+1):
+        for j in range(MAX_UNCONNECTING_HEADERS + 1):
             blocks.append(create_block(tip, create_coinbase(height), block_time))
             blocks[-1].solve()
             tip = blocks[-1].sha256
@@ -554,11 +574,11 @@ class SendHeadersTest(BitcoinTestFramework):
 
         # Now try to see how many unconnecting headers we can send
         # before we get disconnected.  Should be 5*MAX_UNCONNECTING_HEADERS
-        for i in range(5*MAX_UNCONNECTING_HEADERS - 1):
+        for i in range(5 * MAX_UNCONNECTING_HEADERS - 1):
             # Send a header that doesn't connect, check that we get a getheaders.
             with mininode_lock:
                 test_node.last_message.pop("getheaders", None)
-            test_node.send_header_for_blocks([blocks[i%len(blocks)]])
+            test_node.send_header_for_blocks([blocks[i % len(blocks)]])
             test_node.wait_for_getheaders()
 
         # Eventually this stops working.