Emit bedrock events on actions

[aljones15]

Proposal:

After an action happens bedrock-edv-storage will emit an event with data for each event that just occurred. Because the invoker is important events should fire from the HTTP API layer after the event has happened. Currently all we need is an event that fires after a stream has begun.

POST /edvs/:edvId/documents/:docId/chunks/:chunkIndex

const eventData {
  docId,
  edvId,
  invoker,
  controller
}
await bedrodk.emit('bedrock-edv-storage.chunk-post-insert', eventData);

GET /edvs/:edvId/documents/:docId/chunks/:chunkIndex

// only emit on the first chunk to prevent excessive events
if (chunkIndex === 0) {
  const eventData {
    docId,
    edvId,
    invoker,
    controller
  };
  await bedrodk.emit('bedrock-edv-storage.chunk-stream-started', eventData);
}

POST /edvs
Emits:

const eventData = {
  actor,
  controller,
  edvId: id
}
await bedrock.emit('bedrock-edv-storage.edv-post-insert', eventData);

Further events can be added to other endpoints. The chunk one for streams is really the hard one as we can't reliably determine if a stream has finished with out some work.

[dlongley]

Ok, will need some time to review this.

Only immediate thought is that the "we only need to know when a stream started" seems use case specific and the design should not necessarily depend on that, rather, it should support it. For example, we would always emit events when a chunk is read, but some user of that event data may discard events that don't have chunkIndex === 0 (if that's even a good way of doing this).

We also need to do more exploration into what should go into these events and what the model is. Again, it should not be "whatever we need for the current use case" -- rather it should support the current use case. Designing to one particular use case, more often than not, creates significant technical debt.

[aljones15]

That is fine and while I'm at it, we may as well add events for the other actions too. Document read, document write, etc. Just did not have time to write all of them down.