The Linkbox API needs the MD5 of the first 10 MiB of each uploaded
file, so Update reads that prefix into memory before the upload. This
used io.ReadAll, which allocates a fresh heap slice per file and grows
it by doubling, churning well over 10 MiB of garbage per upload.
Read the prefix into a multipart.NewRW buffer instead so the memory
comes from rclone's global pool and is reused across uploads, and hash
it in transit rather than computing the same MD5 twice.
The PUT body goes through lib/rest, which stops the http transport
closing it, so Update owns the buffer and closes it on every exit path.
Nick Craig-Wood
91e7942da5