Design event handler response conventions

[rbennettcw]

When policies or projections throw errors, they may need to be retried since they are not directly invoked by an actor.

Acceptance Criteria

• Documented error conventions for each case:
  • Ack
  • Retry
  • Block
• Utility which wraps a function and handles exceptions appropriately based on error type

[rbennettcw]

Event handler response conventions

• If handler does not throw any error = Ack
• If handler throws any error = Block by default
• Retry strategy is defined with RetryStrategy and enforced with the withRetryStrategy wrapper util function

// reusable strategy which retries on network failure
const networkFailStrategy = new RetryStrategy({
  'Network request failure': {
    maxRetries: 3,
    condition: async (err) => {
      const networkErrors = [
        'ECONNREFUSED', 'ETIMEDOUT', 'EHOSTUNREACH', 'ENETDOWN'
      ];
      return networkErrors.includes(error.code);
    },
  }
});

// multiple strategies can be applied like middleware
const result = await withRetryStrategy([networkFailStrategy], async () => {
  return contractHelpers.doThingThatThrows();
});

// any errors that aren't caught by retry policy = Block

// key = human readable error message, value = retry options
type RetryOptions = Record<string, {
  maxRetries: number;
  condition: (Error) => Promise<boolean>;
}>;

[Rotorsoft]

liking it 💯 ... let's discuss soon

[rbennettcw]

Updating the pattern to allow mapping any error to any strategy for future-proofing (exact naming convention TBD):

const networkFailStrategy = new Strategy({
  'Network request failure': {
    fn: async (err) => {
      const networkErrors = [
        'ECONNREFUSED', 'ETIMEDOUT', 'EHOSTUNREACH', 'ENETDOWN'
      ];
      if (networkErrors.includes(error.code)) {
        return new RetryStrategy({ maxRetries: 3 })
      }
      return null
    },
  }
});

Next steps:

Ticket 1 – Create reusable utility #7637

• Rename it since the name “RetryStrategy” is already in use
• Create the reusable utility that will be used in the Policy + Projection functions
• Implement the utility in the contest worker policy as the first POC

Ticket 2 – Implement in consumer #7638

• The reusable utility should throw a special error that contains the retry config (e.g. error description + max retries)
• In the integration/consumer layer, add logic to detect a ”retriable” error and handle it appropriately