Wrong error code for CompleteMultipartUpload when write condition fails

[findepi]

In Trino project we have a test using S3Mock.

We're upgrading to use S3Mock 4.10.0 to benefit from its support for S3 conditional writes.

We currently have two code paths for conditional writes with If-None-Match: *

• via PutObject request
• via multi-part upload where write condition is verified in CompleteMultipartUpload request

We noticed that in the second code path, when running with S3Mock 4.10.0, we get Status Code: 304 rather than 412 error code.

[afranken]

Did you test this against AWS S3?
We have a few ITs to verify the current behaviour, and those passed against S3 as well (I validate all tests roughly once per year against S3)
https://github.com/search?q=repo%3Aadobe%2FS3Mock%20if-none-match&type=code

[findepi]

Yes, AFAICT same test passed against AWS S3, Minio, LocalStack and Moto

[afranken]

have you had time to test this against S3 yet?