Refresh ReceiveBuffer implementation note

h11/_receivebuffer.py

@@ -20,27 +20,13 @@
 # WARNING:
 # - I haven't benchmarked or profiled any of this yet.
 #
-# Note that starting in Python 3.4, deleting the initial n bytes from a
-# bytearray is amortized O(n), thanks to some excellent work by Antoine
-# Martin:
+# Deleting the initial n bytes from a bytearray is amortized O(n), thanks to
+# some excellent work by Antoine Martin:
 #
 #     https://bugs.python.org/issue19087
 #
-# This means that if we only supported 3.4+, we could get rid of the code here
-# involving self._start and self.compress, because it's doing exactly the same
-# thing that bytearray now does internally.
-#
-# BUT unfortunately, we still support 2.7, and reading short segments out of a
-# long buffer MUST be O(bytes read) to avoid DoS issues, so we can't actually
-# delete this code. Yet:
-#
-#     https://pythonclock.org/
-#
-# (Two things to double-check first though: make sure PyPy also has the
-# optimization, and benchmark to make sure it's a win, since we do have a
-# slightly clever thing where we delay calling compress() until we've
-# processed a whole event, which could in theory be slightly more efficient
-# than the internal bytearray support.)
+# That lets us discard consumed data directly while keeping the total cost
+# linear.
 blank_line_regex = re.compile(b"\n\r?\n", re.MULTILINE)