GCS caching means versions are out of date

[jchesterpivotal]

GCS sets a 3600 second max-age for objects uploaded to GCS buckets:

Unless otherwise specified, the Cache-Control setting for publicly accessible objects is 3600 seconds ... If you allow caching, at download time you might see older versions of objects, even after uploading a newer replacement object, because the older objects remain in the cache for a period of time.

This means that when I put to a semver-resource, I might not be able to successfully get that version back for up to an hour.

This causes some fascinating misbehaviour. The only current workaround is to manually set Cache-Control headers in the bucket. But this means that I have a task following around after every put, which isn't very convenient.

Google suggest setting Cache-Control: private to prevent caching. Can we please see if this improves behaviour?

[rmmh]

Changing the end of driver/gcs.go:PutObject from

return obj.NewWriter(context.Background()), nil

to

w := obj.NewWriter(context.Background())
w.CacheControl = "private"
return w, nil

would fix that.