I discovered that `rclone` always upload in chunks of 16MiB whenever
uploading a file smaller than `--drive-upload-cutoff`. This is
undesirable since the purpose of the flag `--drive-upload-cutoff` is
to *prevent* chunking below a certain file size.
I realized that it wasn't `rclone` forcing the 16MiB chunks. The
`google-api-go-client` forces a chunk size default of
[`googleapi.DefaultUploadChunkSize`](32bf29c2e1/googleapi/googleapi.go (L55-L57))
bytes for resumable type uploads. This means that all requests that
use `*drive.Service` directly for upload without specifying a
`googleapi.ChunkSize` will be forced to use a *`resumable`*
`uploadType` (rather than `multipart`) for files less than
`googleapi.DefaultUploadChunkSize`. This is also noted directly in the
Drive API client documentation [here](https://pkg.go.dev/google.golang.org/api/drive/v3@v0.44.0#FilesUpdateCall.Media).
This fixes the problem by passing `googleapi.ChunkSize(0)` to
`Media()` method calls, which is the only way to disable chunking
completely. This is mentioned in the API docs
[here](https://pkg.go.dev/google.golang.org/api/googleapi@v0.44.0#ChunkSize).
The other alternative would be to pass
`googleapi.ChunkSize(f.opt.ChunkSize)` -- however, I'm *strongly* in
favor of *not* doing this for performance reasons. By not explicitly
passing a `googleapi.ChunkSize(0)`, we effectively allow
[`PrepareUpload()`](https://pkg.go.dev/google.golang.org/api/internal/gensupport@v0.44.0#PrepareUpload)
to create a
[`NewMediaBuffer`](https://pkg.go.dev/google.golang.org/api/internal/gensupport@v0.44.0#NewMediaBuffer)
that copies the original `io.Reader` passed to `Media()` in order to
check that its size is less than `ChunkSize`, which will unnecessarily
consume time and memory.
`minChunkSize` is also changed to be `googleapi.MinUploadChunkSize`,
as it is something specified we have no control over.
269f90c1e4