1 files changed, 40 insertions, 0 deletions
diff --git a/testing/web-platform/tests/websockets/stream/tentative/backpressure-receive.any.js b/testing/web-platform/tests/websockets/stream/tentative/backpressure-receive.any.js
new file mode 100644
index 0000000000..236bb2e40f
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+++ b/testing/web-platform/tests/websockets/stream/tentative/backpressure-receive.any.js
@@ -0,0 +1,40 @@
+// META: script=../../constants.sub.js
+// META: script=resources/url-constants.js
+// META: global=window,worker
+// META: timeout=long
+// META: variant=?wss
+// META: variant=?wpt_flags=h2
+
+// Allow for this much timer jitter.
+const JITTER_ALLOWANCE_MS = 200;
+const LARGE_MESSAGE_COUNT = 16;
+
+// This test works by using a server WebSocket handler which sends a large
+// message, and then sends a second message with the time it measured the first
+// message taking. On the browser side, we wait 2 seconds before reading from
+// the socket. This should ensure it takes at least 2 seconds to finish sending
+// the large message.
+promise_test(async t => {
+  const wss = new WebSocketStream(`${BASEURL}/send-backpressure`);
+  const { readable } = await wss.opened;
+  const reader = readable.getReader();
+
+  // Create backpressure for 2 seconds.
+  await new Promise(resolve => t.step_timeout(resolve, 2000));
+
+  // Skip the empty message used to fill the readable queue.
+  await reader.read();
+
+  // Skip the large messages.
+  for (let i = 0; i < LARGE_MESSAGE_COUNT; ++i) {
+    await reader.read();
+  }
+
+  // Read the time it took.
+  const { value, done } = await reader.read();
+
+  // A browser can pass this test simply by being slow. This may be a source of
+  // flakiness for browsers that do not implement backpressure properly.
+  assert_greater_than_equal(Number(value), 2 - JITTER_ALLOWANCE_MS / 1000,
+                            'data send should have taken at least 2 seconds');
+}, 'backpressure should be applied to received messages');