DLT Event Monitor

Overview

The DLT Event Monitor is a utility that updates pending batches in Grid with the latest information from the DLT. It does this by subscribing to the DLT’s subscription endpoint.

This is useful for two primary purposes:

• Tracking whether the batch submitter needs to resubmit a batch
• Allowing someone who submits a batch to be notified of the current batch status

Input / Output Definition

The DLT polling monitor uses the following inputs:

• subscribe_stream - Normalized stream sourced from Splinter or Sawtooth
• rate_limit - Maximum rate at which polls can occur, as a Duration

And it modifies with the following:

• poll_batch_statuses - Make a request to get the latest batch statuses. This will likely be handled through the DLT Polling Monitor.

Strategy

The DLT event monitor connects to the subscribe_stream via websocket. When a transaction is received, we can be reasonably certain that a batch has completed. We then notify the DLT Polling monitor via poll_batch_statuses. The DLT polling monitor then has the opportunity to immediately poll. Events are rate limited at the rate_limit.

Known limitations

This solution does not provide a method to determine whether a specific transaction has occurred or failed in real time. The subscribe_stream will only send events that are successful, and not send any accompanying batch information. This info will need to come in via the DLT Polling Monitor.

Ideally the DLT streams for Sawtooth and Splinter would be expanded to a more generalized stream that includes not only raw ledger updates, but batch execution information.

Current websocket status format

Scabbard

Stream URL: /scabbard/{circuit_id}/{service_id}/ws/subscribe.

Definition: Scabbard State Delta Events

Example:

{
  "id": "f62b978a8836013b6ceaac8331a7f720ddd837de7333ae14ab0f4adad445118574735afeeea1f98a51254d8750f1769fc18d6c638963af7f66c5b5086545fba1",
  "state_changes": [
    {
      "Set": {
        "key": "00ec00ebfd680ea8abffc272049e01409cda9efec943f4ddca0263897e715913a04705",
        "value": [
          10,
          117,
          10,
          8
	    ]
      }
    }
  ]
}

Sawtooth

Stream URL: /ws/subscribe

Definition: Sawtooth State Delta Events

Example:

{
  "block_num": 8,
  "block_id": "ab7cbc7a...",
  "previous_block_id": "d4b46c1c...",
  "state_changes": [
    {
      "type": "SET",
      "value": "oWZQdmxqcmsZU4w",
      "address": "1cf126613a..."
    }
  ]
}