feat(events): stream Redis invalidations over SSE

lib/events/sse.test.ts

@@ -0,0 +1,47 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+import {
+  createEventStream,
+  eventStreamHeaders,
+  SSE_HEARTBEAT_MS,
+  SSE_MAX_LIFETIME_MS,
+} from "./sse";
+
+const decoder = new TextDecoder();
+
+afterEach(() => {
+  vi.useRealTimers();
+});
+
+describe("SSE stream", () => {
+  it("uses the required heartbeat, reconnect lifetime, and proxy headers", () => {
+    expect(SSE_HEARTBEAT_MS).toBe(90_000);
+    expect(SSE_MAX_LIFETIME_MS).toBe(30 * 60 * 1_000);
+    const headers = eventStreamHeaders();
+    expect(headers.get("content-type")).toContain("text/event-stream");
+    expect(headers.get("cache-control")).toBe("no-cache, no-transform");
+    expect(headers.get("x-accel-buffering")).toBe("no");
+  });
+
+  it("heartbeats, sends only the supplied envelope, and closes on schedule", async () => {
+    vi.useFakeTimers();
+    const onClose = vi.fn();
+    const channel = createEventStream({
+      heartbeatMs: 50,
+      maximumLifetimeMs: 99,
+      onClose,
+    });
+    const reader = channel.stream.getReader();
+
+    expect(decoder.decode((await reader.read()).value)).toBe(": connected\n\n");
+    channel.send({ type: "page.updated", id: "opaque", version: 7 });
+    expect(decoder.decode((await reader.read()).value)).toBe(
+      'event: invalidation\ndata: {"type":"page.updated","id":"opaque","version":7}\n\n',
+    );
+    await vi.advanceTimersByTimeAsync(50);
+    expect(decoder.decode((await reader.read()).value)).toMatch(/^: heartbeat /u);
+    await vi.advanceTimersByTimeAsync(49);
+    expect((await reader.read()).done).toBe(true);
+    expect(onClose).toHaveBeenCalledTimes(1);
+  });
+});