bench: add k6 example script

.gitignore

@@ -31,3 +31,5 @@
 /yarn-error.log
 yarn-debug.log*
 .yarn-integrity
+
+.k6/k6

.k6/README.md

@@ -0,0 +1,23 @@
+# Benchmarking with k6
+
+This folder contains benchmark/stress test scenarios to be used with [k6][].
+
+We rely on the [xk6-cable][] extension, so you must first build a custom k6 executable (following the instructions described in the xk6-cable repo) and keep it in the `.k6/` folder.
+
+## Scenarios
+
+All scenarios support the following env vars:
+
+- `CABLE_URL`: WebSocket connection url (defaults to `ws://localhost:8080/cable`).
+- `WORKSPACE`: Workspace ID.
+
+### `chat.js`
+
+Connect to a chat room, send N (env `NUM` or 5) messages and expect to receive own messages back:
+
+```sh
+./k6 run --vus 20 --duration 10s chat.js
+```
+
+[k6]: https://k6.io
+[xk6-cable]: https://github.com/anycable/xk6-cable

.k6/chat.js

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+import { check, sleep, fail } from "k6";
+import cable from "k6/x/cable";
+import { randomIntBetween } from "https://jslib.k6.io/k6-utils/1.1.0/index.js";
+
+import { Trend } from "k6/metrics";
+
+let rttTrend = new Trend("rtt", true);
+
+let userId = `100${__VU}`;
+let userName = `Kay${userId}`;
+
+const URL = __ENV.CABLE_URL || "ws://localhost:8080/cable";
+const WORKSPACE = __ENV.WORKSPACE || "demo";
+const MESSAGES_NUM = parseInt(__ENV.NUM || "5");
+
+export let options = {
+  thresholds: {
+    checks: ["rate>0.9"],
+  },
+};
+
+export default function () {
+  let client = cable.connect(URL, {
+    cookies: `uid=${userName}/${userId}`,
+  });
+
+  if (
+    !check(client, {
+      "successful connection": (obj) => obj,
+    })
+  ) {
+    fail("connection failed");
+  }
+
+  let channel = client.subscribe("ChatChannel", { id: WORKSPACE });
+
+  if (
+    !check(channel, {
+      "successful subscription": (obj) => obj,
+    })
+  ) {
+    fail("failed to subscribe");
+  }
+
+  for (let i = 0; i < MESSAGES_NUM; i++) {
+    let startMessage = Date.now();
+    channel.perform("speak", { message: `hello from ${userName}` });
+
+    let message = channel.receive({ author_id: userId });
+
+    if (
+      !check(message, {
+        "received its own message": (obj) => obj,
+      })
+    ) {
+      fail("expected message hasn't been received");
+    }
+
+    let endMessage = Date.now();
+    rttTrend.add(endMessage - startMessage);
+
+    sleep(randomIntBetween(5, 10) / 10);
+  }
+
+  client.disconnect();
+}