Island: Add GeventHubErrorHandler to log gevent exceptions

monkey/monkey_island/cc/setup/gevent_hub_error_handler.py

@@ -0,0 +1,26 @@
+import traceback
+
+import gevent.hub
+
+
+class GeventHubErrorHandler:
+    """
+    Wraps gevent.hub.Hub's handle_error() method so that the exception can be
+    logged but the traceback can be stored in a separate file. This preserves
+    the default gevent functionality and adds a useful, concise log message to
+    the Monkey Island logs.
+
+    For more information, see
+        https://github.com/guardicore/monkey/issues/859,
+        https://www.gevent.org/api/gevent.hub.html#gevent.hub.Hub.handle_error
+        https://github.com/gevent/gevent/issues/1482
+    """
+
+    def __init__(self, hub: gevent.hub.Hub, logger):
+        self._original_handle_error = hub.handle_error
+        self._logger = logger
+
+    def __call__(self, context, type_, value, tb):
+        exception_msg = traceback.format_exception_only(type_, value)
+        self._logger.warning(f"gevent caught an exception: {exception_msg}")
+        self._original_handle_error(context, type_, value, tb)