After PUTting a file to the upload URL, Yandex keeps the file locked
for writing until the upload operation finishes committing on the
server. The PUT returned before this happened, so the following
SetModTime raced the still-in-progress write and got spurious 500
Internal Server Error responses.
Capture the operation_id returned with the upload URL and poll the
operation status until it reports success before returning, so the file
is fully committed before we access it.
Nick Craig-Wood
fe78b559d1