added rateLimiter.py, by @felixhandte

this rate limiter avoid the problem of `pv`
which "catch up" after a blocked period
instead of preserving a constant speed cap.

tests/rateLimiter.py

@@ -0,0 +1,33 @@
+#! /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
+
+rate = float(sys.argv[1]) * 1024 * 1024
+start = time.time()
+total_read = 0
+
+buf = " "
+while len(buf):
+  now = time.time()
+  to_read = max(int(rate * (now - start) - total_read), 1)
+  buf = sys.stdin.read(to_read)
+  write_start = time.time()
+  sys.stdout.write(buf)
+  write_end = time.time()
+  start += write_end - write_start
+  total_read += len(buf)