Implement WebTransport.getStats() API

This is a partial implementation, as some of the stats fields are still
under discussion in the W3C WG.

Bug: 1519563
Change-Id: I2949cb3cf8d31bd87b87599520417707a66bceaa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4953098
Commit-Queue: Victor Vasiliev <[email protected]>
Reviewed-by: Domenic Denicola <[email protected]>
Reviewed-by: Adam Rice <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1263183}

webtransport/stats.https.any.js

@@ -0,0 +1,106 @@
+// META: global=window,worker
+// META: script=/common/get-host-info.sub.js
+// META: script=resources/webtransport-test-helpers.sub.js
+
+function validate_rtt_stats(stats) {
+  // The assumption below is that the RTT to localhost is under 5 seconds,
+  // which is fairly generous.
+  assert_greater_than(stats.minRtt, 0, "minRtt");
+  assert_less_than(stats.minRtt, 5 * 1000, "minRtt");
+  assert_greater_than(stats.smoothedRtt, 0, "smoothedRtt");
+  assert_less_than(stats.smoothedRtt, 5 * 1000, "smoothedRtt");
+}
+
+promise_test(async t => {
+  const wt = new WebTransport(webtransport_url('echo.py'));
+  await wt.ready;
+  const stats = await wt.getStats();
+  validate_rtt_stats(stats);
+  assert_equals(stats.datagrams.expiredOutgoing, 0);
+  assert_equals(stats.datagrams.droppedIncoming, 0);
+  assert_equals(stats.datagrams.lostOutgoing, 0);
+}, "WebTransport client should be able to provide stats after connection has been established");
+
+promise_test(async t => {
+  const wt = new WebTransport(webtransport_url('echo.py'));
+  await wt.ready;
+  wt.close();
+
+  const stats = await wt.getStats();
+  validate_rtt_stats(stats);
+}, "WebTransport client should be able to provide stats after connection has been closed");
+
+promise_test(async t => {
+  const wt = new WebTransport(webtransport_url('echo.py'));
+  await wt.ready;
+  const statsPromise = wt.getStats();
+  wt.close();
+
+  const stats = await statsPromise;
+  validate_rtt_stats(stats);
+}, "WebTransport client should be able to provide stats requested right before connection has been closed");
+
+promise_test(async t => {
+  const wt = new WebTransport(webtransport_url('echo.py'));
+  const stats = await wt.getStats();
+  validate_rtt_stats(stats);
+}, "WebTransport client should be able to provide valid stats when requested before connection established");
+
+promise_test(async t => {
+  const wt = new WebTransport("https://webtransport.invalid/");
+  wt.ready.catch(e => {});
+  wt.closed.catch(e => {});
+  const error = await wt.getStats().catch(e => e);
+  assert_equals(error.code, DOMException.INVALID_STATE_ERR);
+  const error2 = await wt.getStats().catch(e => e);
+  assert_equals(error2.code, DOMException.INVALID_STATE_ERR);
+}, "WebTransport client should throw an error when stats are requested for a failed connection");
+
+promise_test(async t => {
+  const wt = new WebTransport(webtransport_url('echo.py'));
+  await wt.ready;
+  const stats1 = wt.getStats();
+  const stats2 = wt.getStats();
+  assert_true(stats1 != stats2, "different promise returned for different getStats() calls");
+  validate_rtt_stats(await stats1);
+  validate_rtt_stats(await stats2);
+}, "WebTransport client should be able to handle multiple concurrent stats requests");
+
+promise_test(async t => {
+  const wt = new WebTransport(webtransport_url('echo.py'));
+  await wt.ready;
+  const stats1 = await wt.getStats();
+  validate_rtt_stats(stats1);
+  const stats2 = await wt.getStats();
+  validate_rtt_stats(stats2);
+}, "WebTransport client should be able to handle multiple sequential stats requests");
+
+promise_test(async t => {
+  const wt = new WebTransport(webtransport_url('echo.py'));
+  await wt.ready;
+
+  const numDatagrams = 64;
+  wt.datagrams.incomingHighWaterMark = 4;
+
+  const writer = wt.datagrams.writable.getWriter();
+  const encoder = new TextEncoder();
+  const promises = [];
+  while (promises.length < numDatagrams) {
+    const token = promises.length.toString();
+    promises.push(writer.write(encoder.encode(token)));
+  }
+  await Promise.all(promises);
+
+  const maxAttempts = 40;
+  let stats;
+  for (let i = 0; i < maxAttempts; i++) {
+    wait(50);
+    stats = await wt.getStats();
+    if (stats.datagrams.droppedIncoming > 0) {
+      break;
+    }
+  }
+  assert_greater_than(stats.datagrams.droppedIncoming, 0);
+  assert_less_than_equal(stats.datagrams.droppedIncoming,
+                         numDatagrams - wt.datagrams.incomingHighWaterMark);
+}, "WebTransport client should be able to provide droppedIncoming values for datagrams");