1#!/usr/bin/python
2
3import time
4
5# The amount of internal buffering a WebSocket connection has is not
6# standardised, and varies depending upon the OS. Setting this number too small
7# will result in false negatives, as the entire message gets buffered. Setting
8# this number too large will result in false positives, when it takes more than
9# 2 seconds to transmit the message anyway. This number was arrived at by
10# trial-and-error.
11MESSAGE_SIZE = 1024 * 1024
12
13# With Windows 10 and Python 3, the OS will buffer an entire message in memory
14# and return from send() immediately, even if it is very large. To work around
15# this problem, send multiple messages.
16MESSAGE_COUNT = 16
17
18
19def web_socket_do_extra_handshake(request):
20    # Turn off permessage-deflate, otherwise it shrinks our big message to a
21    # tiny message.
22    request.ws_extension_processors = []
23
24
25def web_socket_transfer_data(request):
26    # Send empty message to fill the ReadableStream queue
27    request.ws_stream.send_message(b'', binary=True)
28
29    # TODO(ricea@chromium.org): Use time.perf_counter() when migration to python
30    # 3 is complete. time.time() can go backwards.
31    start_time = time.time()
32
33    # The large messages that will be blocked by backpressure.
34    for i in range(MESSAGE_COUNT):
35        request.ws_stream.send_message(b' ' * MESSAGE_SIZE, binary=True)
36
37    # Report the time taken to send the large message.
38    request.ws_stream.send_message(str(time.time() - start_time),
39                                   binary=False)
40