Example: Safe Mutation with Idempotent POST Requests

[cinar]

Description: Retrying a GET request is safe, but retrying a POST request (like executing a trade order or mutating a database record) can result in catastrophic duplicate actions if the network drops the HTTP response. This example demonstrates how to safely retry state-changing HTTP requests using Idempotency Keys.

• Architecture & Implementation Requirements:

  • Setup: Create examples/http_idempotent/main.go.
  • Idempotency Logic: Generate a unique UUID or ULID before the resile.Do loop begins.
  • Header Injection: Inside the retry closure, inject this key into the HTTP request headers (e.g., Idempotency-Key: <uuid>).
  • Error Filtering: Use resile.WithRetryIfFunc to explicitly prevent retrying on 400 Bad Request or 401 Unauthorized, restricting retries exclusively to 500 Internal Server Error, 502 Bad Gateway, or 504 Gateway Timeout.

• Acceptance Criteria:

  • The example must clearly show the difference between transient network errors (which get retried with the same key) and terminal business-logic errors (which push back and abort).
  • Target 90% code coverage on the custom error-filtering function to ensure no unsafe HTTP statuses are accidentally retried.