With busboy 0.2.9 when piping an incomplete multipart to busboy the last (incomplete) part is emitted on source end (field emitted, or file stream end emitted), then busboy stops emitting events (no file end, no finish, no error).
It should instead emit an error: the multipart is invalid (because incomplete) and should not emit the current part, because it's not finished.

head commit e70d9e4 fixes part of this issue: now busboy emits an error (Error: Unexpected end of multipart data), but the current incomplete part is still emitted.
For field events we should just not emit them and emit error on busboy.
For file events we should emit error on file, on busboy or on both, I'm not sure which.
Busboy also emits finish, I'm not sure if we want that in addition to the error event.

I'm not sure how to properly handle errors in a pipe involving multiple streams (in my case: http request incoming message, busboy, aws-sdk S3 upload; the S3 upload needs an explicit abort on source error, and the http request needs a reply): busboy readme doesn't show any error handling example.