Fix evil retry loop on poll errors.

appengine/swarming/swarming_bot/bot_code/remote_client_grpc.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 # This is a reimplementation of RemoteClientNative but it uses (will use)
 # a gRPC method to communicate with a server instead of REST.
 
 import json
 import logging
 
 import grpc
 import google.protobuf.json_format
 from proto_bot import swarming_bot_pb2
 from remote_client_errors import InternalError
+from remote_client_errors import PollError
 
 
 # How long to wait for a response from the server. Keeping the same as
 # the equivalent in remote_client.py for now.
 NET_CONNECTION_TIMEOUT_SEC = 5*60
 
 
 class RemoteClientGrpc(object):
   """RemoteClientGrpc knows how to make calls via gRPC.
   """
@@ skipping 80 matching lines @@
                 d.name: d.values for d in response.bot_group_cfg.dimensions
             },
         },
     }
     logging.info('Completed handshake: %s', resp)
     return resp
 
   def poll(self, attributes):
     request = swarming_bot_pb2.PollRequest()
     self._attributes_json_to_proto(attributes, request.attributes)
-    # TODO(aludwin): gRPC-specific exception handling
+    # TODO(aludwin): gRPC-specific exception handling (raise PollError).
     response = self._stub.Poll(request, timeout=NET_CONNECTION_TIMEOUT_SEC)
 
     if response.cmd == swarming_bot_pb2.PollResponse.UPDATE:
       return 'update', response.version
 
     if response.cmd == swarming_bot_pb2.PollResponse.SLEEP:
       if not self._log_is_asleep:
         logging.info('Going to sleep')
         self._log_is_asleep = True
       return 'sleep', response.sleep_time
@@ skipping 33 matching lines @@
         # These keys are only needed by raw commands. While this method
         # only supports isolated commands, the keys need to exist to avoid
         # missing key errors.
         'command': None,
         'extra_args': None,
       }
       logging.info('Received job manifest: %s', manifest)
       self._log_is_asleep = False
       return 'run', manifest
 
-    raise ValueError('Unknown command in response: %s' % response)
+    raise PollError('Unknown command in response: %s' % response)
 
   def get_bot_code(self, new_zip_fn, bot_version, _bot_id):
     # TODO(aludwin): exception handling, pass bot_id
     logging.info('Updating to version: %s', bot_version)
     request = swarming_bot_pb2.BotUpdateRequest()
     request.bot_version = bot_version
     response = self._stub.BotUpdate(request, timeout=NET_CONNECTION_TIMEOUT_SEC)
     with open(new_zip_fn, 'wb') as f:
       f.write(response.bot_code)
 
@@ skipping 34 matching lines @@
 def insert_dict_as_submessage(message, keyname, value):
   """Encodes a dict as a Protobuf message.
 
   The keyname for the message field is passed in to simplify the creation
   of the submessage in the first place - you need to say getattr and not
   simply refer to message.keyname since the former actually creates the
   submessage while the latter does not.
   """
   sub_msg = getattr(message, keyname)
   google.protobuf.json_format.Parse(json.dumps(value), sub_msg)