S3 Multi-Part-Upload (MPU) is implemented recently in the Ozone s3 gateway. We have extensive testing with using 'aws s3api' application which is passed.
But it turned out that the more simple `aws s3 cp` command fails with 405 Media type not supported error message
The root cause of this issue is the JAXRS implementation of the multipart upload method:
Here we have a CompleteMultipartUploadRequest parameter which is created by the JAXRS framework based on the media type and the request body. With Content-Type: application/xml it's easy: the JAXRS framework uses the built-in JAXB serialization. But with plain/text content-type it's not possible as there is no serialization support for CompleteMultipartUploadRequest from plain/text.