[Drive API] Error 400 when replacing existing file during upload since v3.5.0 about google-api-objectivec-client-for-rest HOT 1 OPEN

So the change you reference moved a user agent calculation off to a worker queue allowing query starting to not block for as long. I.e. - there's a timing change on how fast the start returns vs. when the networking might actually start.

Given the quoted error you are seeing, my guess if you've got a race that you've always had and the timing change just exposed it. The file you are trying to upload was changed between the start call and the completion of the whole upload request, and the update code paths not catch that where as before they didn't.

Generally speaking, you don't want to be mutating a file while you are trying to upload it as then you don't really know what state is getting sent to the server (we don't/can't assume there is space to buffer the file any place). If you are trying to upload a log file or something that you do want to change with time, you'll need to do the buffering your self – i.e. - roll to a new file at the start of each upload and delete the old after completion, or maybe copy the file each time you start an upload, etc.

from google-api-objectivec-client-for-rest.