Makes gcp attributes accessible

[wezzle]

Just like my last pull request adding a function to Subscriber, this pull request adds a function to SubMessage making the underlying attributes sent with GCP accessible.

[coveralls]

Coverage remained the same at 45.194% when pulling 61c2a7c on wezzle:gcp-attributes into 4956979 on NYTimes:master.

[jprobinson]

Unfortunately, this change breaks the interface contract on gizmo/pubsub.Subscriber:

	*Subscriber does not implement "github.com/NYTimes/gizmo/pubsub".Subscriber (wrong type for Start method)
		have Start() <-chan *SubMessage
		want Start() <-chan "github.com/NYTimes/gizmo/pubsub".SubscriberMessage

Is there any way you can encapsulate the information you need inside the message payload? Perhaps an 'envelope'-like struct that holds metadata and the payload?

[wezzle]

Sorry, totally missed that. I'll take another stab at it.

[wezzle]

Ok so i've changed back the interface part to pubsub.Subscriber. The public gcp.SubMessage now has Attributes that is filled on Receive if msg is of type messageImpl to make sure code does not break on type conversion during tests where the msg is of type testMessage.

External code can now use msg.(*gcp.SubMessage).Attributes to access the original GCP Attributes sent with the message itself.

Also i've added a test to prevent future errors with the pubsup.Subscriber interface.

Please let me know if you see anything wrong with this, or any improvements.

[coveralls]

Coverage decreased (-1.2%) to 43.967% when pulling 5d4750c on wezzle:gcp-attributes into 4956979 on NYTimes:master.

[jprobinson]

Ok, I think that's an acceptable workaround for folks who really need the attributes.

Looks like we have some kind of merge conflict on this now. If you can clean that up, I'll pull this in.

[wezzle]

How can I see what the conflict is? The message under this pull-request shows there are no conflicts with the base branch?

[jprobinson]

Ah, it just wouldn't let me 'rebase and merge'. Squashing and merging...

[jprobinson]

🌮 thanks again!