[xray] Add error table and push error messages to driver through node manager. (#2256)

* Fix documentation indentation.

* Add error table to GCS and push error messages through node manager.

* Add type to error data.

* Linting

* Fix failure_test bug.

* Linting.

* Enable one more test.

* Attempt to fix doc building.

* Restructuring

* Fixes

* More fixes.

* Move current_time_ms function into util.h.

python/ray/gcs_utils.py

@@ -0,0 +1,84 @@
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import flatbuffers
+
+from ray.core.generated.ResultTableReply import ResultTableReply
+from ray.core.generated.SubscribeToNotificationsReply \
+    import SubscribeToNotificationsReply
+from ray.core.generated.TaskExecutionDependencies import \
+    TaskExecutionDependencies
+from ray.core.generated.TaskReply import TaskReply
+from ray.core.generated.DriverTableMessage import DriverTableMessage
+from ray.core.generated.LocalSchedulerInfoMessage import \
+    LocalSchedulerInfoMessage
+from ray.core.generated.SubscribeToDBClientTableReply import \
+    SubscribeToDBClientTableReply
+from ray.core.generated.TaskInfo import TaskInfo
+
+import ray.core.generated.ErrorTableData
+
+from ray.core.generated.GcsTableEntry import GcsTableEntry
+from ray.core.generated.ClientTableData import ClientTableData
+from ray.core.generated.ErrorTableData import ErrorTableData
+from ray.core.generated.HeartbeatTableData import HeartbeatTableData
+from ray.core.generated.ObjectTableData import ObjectTableData
+from ray.core.generated.ray.protocol.Task import Task
+
+from ray.core.generated.TablePrefix import TablePrefix
+from ray.core.generated.TablePubsub import TablePubsub
+
+__all__ = [
+    "SubscribeToNotificationsReply", "ResultTableReply",
+    "TaskExecutionDependencies", "TaskReply", "DriverTableMessage",
+    "LocalSchedulerInfoMessage", "SubscribeToDBClientTableReply", "TaskInfo",
+    "GcsTableEntry", "ClientTableData", "ErrorTableData", "HeartbeatTableData",
+    "ObjectTableData", "Task", "TablePrefix", "TablePubsub",
+    "construct_error_message"
+]
+
+# These prefixes must be kept up-to-date with the definitions in
+# ray_redis_module.cc.
+DB_CLIENT_PREFIX = "CL:"
+TASK_PREFIX = "TT:"
+OBJECT_CHANNEL_PREFIX = "OC:"
+OBJECT_INFO_PREFIX = "OI:"
+OBJECT_LOCATION_PREFIX = "OL:"
+FUNCTION_PREFIX = "RemoteFunction:"
+
+# These prefixes must be kept up-to-date with the TablePrefix enum in gcs.fbs.
+# TODO(rkn): We should use scoped enums, in which case we should be able to
+# just access the flatbuffer generated values.
+TablePrefix_RAYLET_TASK_string = "RAYLET_TASK"
+TablePrefix_OBJECT_string = "OBJECT"
+TablePrefix_ERROR_INFO_string = "ERROR_INFO"
+
+
+def construct_error_message(error_type, message, timestamp):
+    """Construct a serialized ErrorTableData object.
+
+    Args:
+        error_type: The type of the error.
+        message: The error message.
+        timestamp: The time of the error.
+
+    Returns:
+        The serialized object.
+    """
+    builder = flatbuffers.Builder(0)
+    error_type_offset = builder.CreateString(error_type)
+    message_offset = builder.CreateString(message)
+
+    ray.core.generated.ErrorTableData.ErrorTableDataStart(builder)
+    ray.core.generated.ErrorTableData.ErrorTableDataAddType(
+        builder, error_type_offset)
+    ray.core.generated.ErrorTableData.ErrorTableDataAddErrorMessage(
+        builder, message_offset)
+    ray.core.generated.ErrorTableData.ErrorTableDataAddTimestamp(
+        builder, timestamp)
+    error_data_offset = ray.core.generated.ErrorTableData.ErrorTableDataEnd(
+        builder)
+    builder.Finish(error_data_offset)
+
+    return bytes(builder.Output())