A distributed query campaign can be "orphaned" (left in the QueryRunning state)
if the Kolide server restarts while it is running, or other weirdness occurs.
When this happens, no subscribers are waiting to read results written by
osqueryd agents, but the agents continue to receive the query. Previously, this
would cause us to error on ingestion.
The new behavior will instead set the campaign to completed when it detects
that it is orphaned. This should prevent sending queries for which there is no
subscriber.
- New NoSubscriber error interface in pubsub
- Detect NoSubscriber errors and close campaigns
- Tests on pubsub and service methods
Fixes#695
A new datastore interface is needed for buffering incoming distributed query results to be sent to the client. This PR attempts to define and implement that interface.
It is intended that the ReadChannel() method be used by the goroutine that will push query results down a websocket to the client. Passing the results through this channel will allow that goroutine to perform a select on both the channel and the websocket, in order to properly handle IO.
