Merge #12902: [qa] Handle potential cookie race when starting node

75d0e4c544 [qa] Delete cookie file before starting node (Suhas Daftuar)

Pull request description:

  When a node is restarted during a test after an unclean shutdown (such
  as with -dbcrashratio), it's possible an old cookie file was left
  behind. This can cause a race condition when restarting the node, where
  the test framework might try to connect using credentials from the
  old cookie file, just as the node will generate new credentials and
  overwrite the old file.

  Delete any such cookie file if present prior to startup.

Tree-SHA512: ae1e8bf8fd20e07c32b0715025693bb28b0e3dd34f328cae4346abf579b0c97b5db1c02782e1c46b7a3b6058d268b6d46b668e847658a6eed0be857ffb0d65dc

test/functional/test_framework/test_node.py

@@ -20,6 +20,7 @@ from .authproxy import JSONRPCException
 from .util import (
     append_config,
     assert_equal,
+    delete_cookie_file,
     get_rpc_proxy,
     rpc_url,
     wait_until,
@@ -116,6 +117,10 @@ class TestNode():
             extra_args = self.extra_args
         if stderr is None:
             stderr = self.stderr
+        # Delete any existing cookie file -- if such a file exists (eg due to
+        # unclean shutdown), it will get overwritten anyway by bitcoind, and
+        # potentially interfere with our attempt to authenticate
+        delete_cookie_file(self.datadir)
         self.process = subprocess.Popen(self.args + extra_args, stderr=stderr, *args, **kwargs)
         self.running = True
         self.log.debug("bitcoind started, waiting for RPC to come up")