I found if upload large file, a file in /tmp will keep forevery until next booting.
But go net/server package will call RemoveAll when request finished(https://github.com/golang/go/blob/b5d555991ab73e06e09741952a66dd7eeaf2a185/src/net/http/server.go#L1700)

	if w.req.MultipartForm != nil {
		w.req.MultipartForm.RemoveAll()
	}

My request and response seem work, but /tmp/multipart-xxxx file not delete by net/server. If i mannual call RemoveAll, it work ok.