https://mattermost.atlassian.net/browse/MM-10677 was resolved by loading the stream back into a buffer to extract the length, and fix the parameter being passed to the S3 library.

An alternative is to re-implement a multi-part fileupload as described in https://github.com/minio/minio-go/issues/848 and chunk the stream instead. This would avoid allocating another file-size buffer in cases where large files are being uploaded.

Reach out to jesse.hallam on pre-release if you have any questions.