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pyln: Add safe fallback results for hooks

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Hooks do not tolerate failures at all. If we return a JSON-RPC error to a hook
call the only thing the main daemon can really do is to crash. This commit
adds a mapping of error to a safe fallback result, including a warning to the
node operator that this should be addressed in the plugin. The warning is
reported as a `**BROKEN**` message, and should therefore fail any testing done
on the plugin.

Changelog-Fixed: pyln: Fixed HTLCs hanging indefinitely if the hook function raises an exception. A safe fallback result is now returned instead.
This commit is contained in:
Christian Decker 2020-09-09 14:37:28 +02:00 committed by Rusty Russell
parent 3d6c4e93b3
commit bd811fbd1a
2 changed files with 32 additions and 2 deletions
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31
contrib/pyln-client/pyln/client/plugin.py
View File

@ -97,6 +97,26 @@ class Request(dict):
self.plugin._write_locked(result) self.plugin._write_locked(result)
# If a hook call fails we need to coerce it into something the main daemon can
# handle. Returning an error is not an option since we explicitly do not allow
# those as a response to the calls, otherwise the only option we have is to
# crash the main daemon. The goal of these is to present a safe fallback
# should the hook call fail unexpectedly.
hook_fallbacks = {
'htlc_accepted': {
'result': 'fail',
'failure_message': '2002' # Fail with a temporary node failure
},
'peer_connected': {'result': 'continue'},
# commitment_revocation cannot recover from failing, let lightningd crash
# db_write cannot recover from failing, let lightningd crash
'invoice_payment': {'result': 'continue'},
'openchannel': {'result': 'reject'},
'rpc_command': {'result': 'continue'},
'custommsg': {'result': 'continue'},
}
class Plugin(object): class Plugin(object):
"""Controls interactions with lightningd, and bundles functionality. """Controls interactions with lightningd, and bundles functionality.
@ -453,6 +473,17 @@ class Plugin(object):
# return a result or raise an exception. # return a result or raise an exception.
request.set_result(result) request.set_result(result)
except Exception as e: except Exception as e:
if name in hook_fallbacks:
response = hook_fallbacks[name]
self.log((
"Hook handler for {name} failed with an exception. "
"Returning safe fallback response {response} to avoid "
"crashing the main daemon. Please contact the plugin "
"author!"
).format(name=name, response=response), level="error")
request.set_result(response)
else:
request.set_exception(e) request.set_exception(e)
self.log(traceback.format_exc()) self.log(traceback.format_exc())

1
tests/test_plugin.py
View File

@ -1860,7 +1860,6 @@ def test_dev_builtin_plugins_unimportant(node_factory):
n.rpc.plugin_stop(plugin="pay") n.rpc.plugin_stop(plugin="pay")
@pytest.mark.xfail(strict=True)
def test_htlc_accepted_hook_crash(node_factory, executor): def test_htlc_accepted_hook_crash(node_factory, executor):
"""Test that we do not hang incoming HTLCs if the hook plugin crashes. """Test that we do not hang incoming HTLCs if the hook plugin crashes.