#!/usr/bin/env python3

# ################################################################
# Copyright (c) 2018-present, Facebook, Inc.
# All rights reserved.
#
# This source code is licensed under both the BSD-style license (found in the
# LICENSE file in the root directory of this source tree) and the GPLv2 (found
# in the COPYING file in the root directory of this source tree).
# ##########################################################################

# Rate limiter, replacement for pv
# this rate limiter does not "catch up" after a blocking period
# Limitations:
# - only accepts limit speed in MB/s

import sys
import time

MB = 1024 * 1024
rate = float(sys.argv[1]) * MB
rate *= 1.25   # compensation for excluding write time (experimentally determined)
start = time.time()
total_read = 0

buf = " "
while len(buf):
  now = time.time()
  to_read = max(int(rate * (now - start) - total_read), 1)
  max_buf_size = 1 * MB
  to_read = min(to_read, max_buf_size)
  buf = sys.stdin.buffer.read(to_read)
  write_start = time.time()
  sys.stdout.buffer.write(buf)
  write_end = time.time()
  start += write_end - write_start   # exclude write delay
  total_read += len(buf)