Add more useful header info on HTTP requests

[dhermes]

Most relevant place: https://github.com/GoogleCloudPlatform/google-cloud-python/blob/9619004959def22ad2084691f382dc1cada46afd/core/google/cloud/_http.py#L177

May want to make this easier to use upstream

/cc @lukesneeringer

[tseaver]

Seems like we could override the USER_AGENT class attribute for the APIs which use JSONConnection, and derive it from pkg_resources (maybe add a helper for that?). E.g.:

from pkg_resources import get_distribution

from google.cloud._http import JSONConnection


class Connection(JSONConnection):
    USER_AGENT = 'google-cloud-foo-python/{0}'.format(
        get_distribution('google-cloud-foo').version)

I don't know whether the -python suffix should be there. @lukesneeringer can you confirm?

[lukesneeringer]

It is actually moving to a new header, X-Goog-API-Client, and the client library is going to be abbreviated gccl (google cloud client library).

We also intend to track the language via gl-python/{v}, which should appear at the beginning of the string. GAX already does this, but the HTTP base client will need to add it, too.

We probably still need to set a User-Agent string (just because it is considered good practice), and it does not matter what it is. google-cloud-core/{v} seems appropriate for that but I will defer to whatever you folks want (provided it is sane).

[dhermes]

@lukesneeringer The value of gcloud-python used to be deemed "sacred" to preserve some reporting internal to Google. That may no longer be true.

[lukesneeringer]

This is no longer true. The new header is superceding the old one.

[dhermes]

#3035 is most of the "intellectual conceptual way" towards this

[dhermes]

Remaining APIs:

• bigquery
• datastore
• dns
• error_reporting
• language
• logging
• monitoring
• pubsub
• resource_manager
• runtimeconfig
• speech
• storage
• translate
• vision