Here, if an error occurs, the connector picks the default option, which may not be something that all users want. Would it be better to gate using the default options behind some kind of flag?

Good point, I'll change these to return hard errors on invalid config

If someone chooses number of messages for file rotation and forgets to define max_messages_per_file, max messages will be set to u64::MAX, which means that processes other than the connector will force the flush to s3, which I believe is not an ideal situation.

I'll add a validation in open() that returns an error if file_rotation = "messages" but max_messages_per_file is not set. do you think this is a good approach?

I think that is a good approach. In addition, how about erroring hard in let max_messages = self.config.max_messages_per_file.unwrap_or(u64::MAX); instead of passing u64::MAX as a fallback?

Wouldn't it be better to inline this function? As far as I can see, it is being used in only one place. You could add a comment instead saying that this piece of code validates the creds.

yeah fair enough

Wouldn't using From for OutputFormat make more sense here? (though the current version also works just fine)

I'll implement TryFrom<&str> for OutputFormat which is more idiomatic

"deterministic S3 keys ... idempotent crash recovery" is false on three grounds:

• path.rs:64 substitutes {timestamp} via Utc::now().timestamp_millis() at render time, so retries produce different keys
• buffer.rs is in-memory only with no WAL, so a process restart cannot reproduce the same batch boundaries
• runtime auto-commits offsets on poll (bug(connectors): PollingMessages auto-commit commits offsets before sink processing #2928) and the FFI return code is discarded (bug(connectors): consume() return value discarded in sink runtime #2927), so replay never happens anyway

either remove the claim, or remove {timestamp} from the template and document the in-memory loss path honestly.

"retry with exponential backoff" - code at sink.rs:260 is retry_delay * attempts, which is linear (1s, 2s, 3s). either update the doc to "linear backoff" or implement retry_delay * 2u32.pow(attempts - 1) with jitter. also AFAIR there is backoff in connectors SDK, please check it.

this paragraph claims at-least-once and then admits "data loss can occur" in the same sentence - that is self-contradictory. given #2927 + #2928, no sink connector can deliver at-least-once today. the canonical in-tree wording is http_sink/README.md:790-800 which honestly documents at-most-once and cites both bugs. recommend copying that section verbatim.

iggy_common is declared under [dependencies] but the only usage in this crate is formatter.rs:233-235 under #[cfg(test)]. move it to [dev-dependencies] so it does not bloat the cdylib build.

missing publish = false. every other connector sink (postgres_sink, delta_sink, http_sink, elasticsearch_sink, stdout_sink) declares publish = false because they are cdylib plugins not meant for crates.io. without it the crate would publish on the next workspace release.

state.messages_processed += messages.len() as u64 runs unconditionally outside the rotate loop, so when a mid-batch flush dropped N messages this counter still claims it processed them. upload_errors increments separately at :209. result: the close-log at :155-156 reports more messages processed than actually landed in S3. either decrement on drop or split into messages_buffered / messages_uploaded / messages_lost.

this is the worst data-loss path in the PR. on retry-exhaust the failure branch logs an error and then calls buffer.reset() at :214 to drop the messages, while consume at :126 still returns Ok(()). the comment at :211-213 claims "offsets will be re-delivered by the runtime on next poll since consume() returned Ok" - that is doubly false:

• the runtime auto-commits offsets before consume runs (runtime/sink.rs:421 uses AutoCommitWhen::PollingMessages, see bug(connectors): PollingMessages auto-commit commits offsets before sink processing #2928), so the offset has already advanced past these messages by the time you return.
• the runtime discards the consume FFI return code (runtime/sink.rs:585-593, see bug(connectors): consume() return value discarded in sink runtime #2927), so even returning Err wouldn't trigger retry today.

net result: a single transient S3 hiccup that exhausts max_retries (default 3) permanently loses every buffered message. the README at line 139 acknowledges this but still claims at-least-once on the same line.

minimum: drop the false comment, propagate Err to the runtime, and align the README with http_sink/README.md:790-800 (at-most-once + cite #2927 / #2928).

attempts starts at 0 and increments before the >= max_retries check, so max_retries = 3 yields 3 total attempts (2 retries past the initial one). this matches the postgres_sink pattern but the field name is misleading. either rename to max_attempts or use attempts > max_retries so the field name lines up with semantics.

the retry loop treats every non-2xx status uniformly. AWS permanent failures - AccessDenied (403), NoSuchBucket (404), InvalidBucketName (400), MalformedPolicy - get retried 3 times, wasting retry_delay * (1 + 2) = 3s before the final Err. classify retriable vs not: 5xx + 408 + 429 + 503 SlowDown -> retry; other 4xx -> fail fast.

retry_delay * attempts is linear backoff (1s, 2s, 3s), but the README at line 13 advertises exponential. either implement retry_delay * 2u32.pow(attempts - 1) with jitter, or update the doc to "linear".

separately, Duration::Mul<u32> panics on overflow - default config is safe but pathological values (e.g. retry_delay = "1h" + large max_retries) would panic. saturating_mul is cheap defensive practice.