The DefaultPartHttpMessageReader has a streaming mode, where the contents of the uploaded parts is not stored in memory or on disk, but directly passed on to the subscriber (in the form of DataBuffers ). However, there is problems in the way streaming mode deals with back pressure, as described in #28006.
Having gone through several milestones, now it is time to deprecate DefaultPartHttpMessageReader's streaming mode, in favor of the PartEvent and PartEventHttpMessageReader introduced through #28006.