Error passing 'fields' to pubsub GET API for subscription

@dhermes

$ tox -e regression --notest
GLOB sdist-make: /home/tseaver/projects/agendaless/Google/src/gcloud-python/setup.py
regression inst-nodeps: /home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/dist/gcloud-0.4.3.zip
___________________________________ summary ____________________________________
  regression: skipped tests
  congratulations :)
$ .tox/regression/bin/python regression/run_regression.py --package=pubsub
test_create_subscription (pubsub.TestPubsub) ... ERROR
test_create_topic (pubsub.TestPubsub) ... ok
test_list_subscriptions (pubsub.TestPubsub) ... ok
test_list_topics (pubsub.TestPubsub) ... ok
test_message_pull_mode_e2e (pubsub.TestPubsub) ... ERROR

ERROR: test_create_subscription (pubsub.TestPubsub)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/regression/pubsub.py", line 74, in test_create_subscription
    self.assertFalse(subscription.exists())
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression/lib/python2.7/site-packages/gcloud/pubsub/subscription.py", line 112, in exists
    query_params={'fields': 'name'})
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression/lib/python2.7/site-packages/gcloud/connection.py", line 293, in api_request
    raise make_exception(response, content)
gcloud.exceptions.BadRequest: 400 Invalid JSON payload received. Unknown name "fields": Cannot bind query parameter.

I omitted a similar failure in another test: both are for a call to subscription.exists() where the expected value is False.

@dhermes this is the one I was working around in #794

@jgeewax maybe tag w/ "google bug"?

@tmatsuo

Whoa! @tmatsuo note that fields is in the discovery doc, but does not actually work when used.

@tseaver Shall we "fix" be re-implementing your previous commit? (PS Good thing exception handling is finally working the way we want :))

Caused breakage in regression tests on master:

https://travis-ci.org/GoogleCloudPlatform/gcloud-python/builds/57382647

Interestingly, the second failure I saw does not appear there. #heisenbug

@tmatsuo

It would be nice to have confirmation that fields is not expected to be passed for non-existing subscriptions. @tmatsuo can you comment?

@tseaver

Actually it is the first time I'm aware of the fields query parameter.
@tseaver
Let me confirm, does this succeed with existing subscription, and fail with non-existing subscriptions?

@tmatsuo

@tmatsuo I just tweaked our regression test to avoid the call for non-existing subscription, and saw the same failure for an existing subscription.

I think this is a bug within the new API infrastructure. I'll file a bug internally.

I can provoke the 400 by supplying name in the fields input on the try it page

Thanks! Filed a bug with an id: 20091445 internally

I got a response.

"""
Could you try "$fields" instead?
"""

Actually I don't like the answer, but could you try it as suggested, just to see if it works?

Using {"$fields": "name"} as query_params prevents the 400.

Thanks for confirming.

JFYI, if the fields -> $fields change is an official thing, we still need to fix bunch of things.

API explorer shows "fields" query param and there is no way to override it.
Documentations need to be updated
- https://developers.google.com/discovery/v1/using
- https://developers.google.com/discovery/v1/parameters

Do you have any opinions about it?

@tseaver

It seems like a fix of something that wasn't broken.
The discovery document still says fields:

"fields": {
 "type": "string",
 "description": "Selector specifying which fields to include in a partial response.",
 "location": "query"
},

Does the APIs Explorer even have an owner?
Note that @tseaver said the API accepted fields when the subscription existed and $fields when it did not.