A Backend for Frontend often calls several services in parallel. Some fields are required for the screen to be valid, while optional fields may use a fallback when their service fails or misses the deadline.
Design a BffResponseComposer class with compose(fields, required, latenciesMs, outcomes, deadlineMs).
The aligned arrays describe parallel calls:
required[i] is 1 when field i is required and 0 when it is optional.outcomes[i] is "success" or "failure".latenciesMs[i] is when that result would arrive.
Classify a call as:
ok when it succeeds at or before the deadline.unavailable when it fails at or before the deadline.timeout when its latency is greater than the deadline, regardless of its eventual outcome.
Its settlement time is its latency for ok or unavailable, and deadlineMs for a timeout.
If required data is unavailable, return one string: FAILED:field:reason@time. Select the unavailable required field with the earliest settlement time, keeping input order on a tie. The BFF fails as soon as that result is known.
Otherwise return READY:time, followed by field:ok, field:unavailable, or field:timeout for every field in input order. Because calls run in parallel, ready time is the maximum settlement time, not their sum. An empty fan-out returns ["READY:0"].
Example 1:
Example 2:
Constraints
0 <= fields.length == required.length == latenciesMs.length == outcomes.length <= 10^5- Field names are unique and contain
1 to 40 printable non-space characters. required[i] is 0 or 1.outcomes[i] is "success" or "failure".0 <= latenciesMs[i] <= 10^9, 1 <= deadlineMs <= 10^9- At most
100 calls are made to compose.
Compose a Partial BFF Responsemedium