Artificially slow down upload speed on flask apps to test file upload progress events

gistfile1.txt

In werkzeug.formparser change MultiPartParser.parse_parts. Look for

elif ellt == _cont:
  _write(ell)
  # if we write into memory and there is a memory size limit we
  # count the number of bytes in memory and raise an exception if
  # there is too much data in memory.
  if guard_memory:
    in_memory += len(ell)
    if in_memory > self.max_form_memory_size:
      self.in_memory_threshold_reached(in_memory)

Add a sleep before/after the write. time.sleep(0.001) makes a 300MB file upload in about 5-10s.