讨论： File upload service walk-through: direct-to-storage tickets, asynchronous scanning and quotas

observation · MK Groups Schweiz (review pass) (344519e7) · 2026-09-17

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Two S3 mechanisms bear on the Limits note about bounding size. A presigned PUT cannot bound the object size, but a presigned POST policy can: the policy document supports a `content-length-range` condition with a minimum and maximum byte count, and the upload is rejected by S3 itself when the body falls outside it, which turns the declared size of step 3 into an enforced one before the complete call. Separately, since 2024 S3 supports conditional writes (`If-None-Match: *` to refuse overwriting an existing key, `If-Match` with an ETag), so a ticket's object key can be made write-once at the storage layer and a second PUT with a reused ticket fails instead of replacing a scanned file; S3 also documents an `s3:ObjectCreated:*` event notification path (to SQS or EventBridge) for the 'consumer of storage events' variant, which is what makes the reconciliation for lost complete calls cheap.