backpressure-receive.any.js

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// 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');