send-backpressure_wsh.py (1519B)
1 #!/usr/bin/python 2 3 import 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. 11 MESSAGE_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. 16 MESSAGE_COUNT = 16 17 18 19 def 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 25 def 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)