GAX can't log nested structs

[waprin]

This is the root issue in #2521 , if we feel it's the same issue can just rename that one. But when using gax,

from google.cloud import logging
client = logging.Client()
logger = client.logger('errors')

payload = {
    'a': {
        'b': 'c',
    }
}
logger.log_struct(payload)

produces:

  File "e.py", line 22, in <module>
    logger.log_struct(payload)
  File "/Users/waprin/.virtualenvs/tasks/lib/python2.7/site-packages/google/cloud/logging/logger.py", line 226, in log_struct
    client.logging_api.write_entries([entry_resource])
  File "/Users/waprin/.virtualenvs/tasks/lib/python2.7/site-packages/google/cloud/logging/_gax.py", line 108, in write_entries
    entry_pbs = [_log_entry_mapping_to_pb(entry) for entry in entries]
  File "/Users/waprin/.virtualenvs/tasks/lib/python2.7/site-packages/google/cloud/logging/_gax.py", line 607, in _log_entry_mapping_to_pb
    entry_pb.json_payload[key] = value
  File "/Users/waprin/.virtualenvs/tasks/lib/python2.7/site-packages/google/protobuf/internal/well_known_types.py", line 732, in __setitem__
    _SetStructValue(self.fields[key], value)
  File "/Users/waprin/.virtualenvs/tasks/lib/python2.7/site-packages/google/protobuf/internal/well_known_types.py", line 702, in _SetStructValue
    raise ValueError('Unexpected type')
ValueError: Unexpected type

[tseaver]

@dhermes I don't think this is actually a GAX/gRPC issue: our own _log_entry_mapping_to_pb function is likely at fault.

[daspecster]

It looks like this causes jsonPayload to be set for when _log_entry_mapping_to_pb() is called later.

This mapping in _log_entry_mapping_to_pb() should probably either be recursive or support some number of levels.

    if 'jsonPayload' in mapping:
        for key, value in mapping['jsonPayload'].items():
            entry_pb.json_payload[key] = value

@dhermes & @waprin WDYT of this over #2553?

[waprin]

SGTM. Bit surprising that that recursively setting a struct needs to be done manually, still trying to understand it.

[daspecster]

@waprin, it looks like the generated code side only accepts bool, text, and number types.

However the docs make it sound like jsonPayload should just accept the object.
https://cloud.google.com/logging/docs/api/ref_v2beta1/rest/v2beta1/LogEntry

Maybe the payload needs to be serialized first?

@bjwatson do you know if this is a bug we should add on googleapis/googleapis or if jsonPayload needs to be converted to a string first?

[bjwatson]

@daspecster I think this is because json_payload is not defined in the proto as map<string, string> like labels is. Instead it is defined as google.protobuf.Struct, which adds one more level to the object hierarchy.

Change this code:

    if 'jsonPayload' in mapping:
        for key, value in mapping['jsonPayload'].items():
            entry_pb.json_payload[key] = value

To something like:

    if 'jsonPayload' in mapping:
        fields = {}
        for key, value in mapping['jsonPayload'].items():
            fields[key] = value
        entry_pb.json_payload = google.protobuf.Struct(fields)