1 files changed, 39 insertions, 0 deletions
diff --git a/testing/web-platform/tests/websockets/handlers/send-backpressure_wsh.py b/testing/web-platform/tests/websockets/handlers/send-backpressure_wsh.py
new file mode 100755
index 0000000000..d3288d0e85
--- /dev/null
+++ b/testing/web-platform/tests/websockets/handlers/send-backpressure_wsh.py
@@ -0,0 +1,39 @@
+#!/usr/bin/python
+
+import time
+
+# The amount of internal buffering a WebSocket connection has is not
+# standardised, and varies depending upon the OS. Setting this number too small
+# will result in false negatives, as the entire message gets buffered. Setting
+# this number too large will result in false positives, when it takes more than
+# 2 seconds to transmit the message anyway. This number was arrived at by
+# trial-and-error.
+MESSAGE_SIZE = 1024 * 1024
+
+# With Windows 10 and Python 3, the OS will buffer an entire message in memory
+# and return from send() immediately, even if it is very large. To work around
+# this problem, send multiple messages.
+MESSAGE_COUNT = 16
+
+
+def web_socket_do_extra_handshake(request):
+    # Turn off permessage-deflate, otherwise it shrinks our big message to a
+    # tiny message.
+    request.ws_extension_processors = []
+
+
+def web_socket_transfer_data(request):
+    # Send empty message to fill the ReadableStream queue
+    request.ws_stream.send_message(b'', binary=True)
+
+    # TODO(ricea@chromium.org): Use time.perf_counter() when migration to python
+    # 3 is complete. time.time() can go backwards.
+    start_time = time.time()
+
+    # The large messages that will be blocked by backpressure.
+    for i in range(MESSAGE_COUNT):
+        request.ws_stream.send_message(b' ' * MESSAGE_SIZE, binary=True)
+
+    # Report the time taken to send the large message.
+    request.ws_stream.send_message(str(time.time() - start_time),
+                                   binary=False)