push updated state to clients over SSE (ISS-129)

app/api/events/route.test.ts

@@ -0,0 +1,41 @@
+import fs from 'node:fs/promises';
+import os from 'node:os';
+import path from 'node:path';
+import { afterAll, beforeAll, describe, expect, it } from 'vitest';
+import { GET } from './route';
+
+let dir: string;
+
+beforeAll(async () => {
+  // Same pattern as app/api/state/route.test.ts: point the DB singleton at a throwaway file so
+  // this test never touches ./db/flight.db. getGameDb() reads the env var on first call, and
+  // vitest gives each test file its own module registry (fresh singleton).
+  dir = await fs.mkdtemp(path.join(os.tmpdir(), 'flight-events-'));
+  process.env.FLIGHT_DB_PATH = path.join(dir, 'events.db');
+});
+
+afterAll(async () => {
+  delete process.env.FLIGHT_DB_PATH;
+  await fs.rm(dir, { recursive: true, force: true });
+});
+
+describe('GET /api/events', () => {
+  it('streams SSE with the current snapshot as the first event', async () => {
+    const res = await GET();
+    expect(res.status).toBe(200);
+    expect(res.headers.get('content-type')).toContain('text/event-stream');
+    expect(res.headers.get('cache-control')).toBe('no-cache');
+    expect(res.headers.get('x-accel-buffering')).toBe('no');
+
+    const reader = (res.body as ReadableStream<Uint8Array>).getReader();
+    try {
+      const { value } = await reader.read(); // first chunk: the initial snapshot event
+      const text = new TextDecoder().decode(value);
+      expect(text.startsWith('data: ')).toBe(true);
+      const snap = JSON.parse(text.slice('data: '.length)) as Record<string, unknown>;
+      expect(typeof (snap.simState as { clockMs: number }).clockMs).toBe('number');
+    } finally {
+      await reader.cancel(); // → stream cancel → unsubscribe from the registry
+    }
+  });
+});

app/api/events/route.ts

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+import { getStateSnapshot } from '@/lib/game/state';
+import { subscribe } from '@/lib/sse';
+
+// ISS-129 (v0.57.0): Server-Sent Events feed of full state snapshots — the current snapshot on
+// connect, then one after every sim tick (broadcast from lib/sim/engine.ts). One-way push; player
+// actions stay REST POSTs. Heartbeats keep idle proxies from dropping the connection.
+
+const encoder = new TextEncoder();
+const HEARTBEAT_MS = 15_000;
+
+export async function GET() {
+  let heartbeat: ReturnType<typeof setInterval> | null = null;
+  let unsubscribe: (() => void) | null = null;
+  const cleanup = () => {
+    if (heartbeat !== null) clearInterval(heartbeat);
+    if (unsubscribe !== null) unsubscribe();
+  };
+
+  const stream = new ReadableStream<Uint8Array>({
+    start(controller) {
+      // Snapshot FIRST, then subscribe — a broadcast can never land before the initial event, so
+      // events are strictly ordered by sim clock. A tick in the gap just means the client waits ≤1 s
+      // for the next push instead of seeing an out-of-order frame.
+      getStateSnapshot()
+        .then((snapshot) => {
+          unsubscribe = subscribe((text) => {
+            try {
+              // broadcast carries the bare snapshot JSON — wrap it in an SSE frame here (the route owns
+              // wire framing, matching the initial snapshot + heartbeat above; lib/sse stays generic).
+              controller.enqueue(encoder.encode(`data: ${text}\n\n`));
+            } catch {
+              // stream already closed — cleanup runs on cancel
+            }
+          });
+          heartbeat = setInterval(() => {
+            try {
+              controller.enqueue(encoder.encode(': ping\n\n'));
+            } catch {
+              // same as above
+            }
+          }, HEARTBEAT_MS);
+          controller.enqueue(encoder.encode(`data: ${JSON.stringify(snapshot)}\n\n`));
+        })
+        .catch(() => {
+          cleanup();
+          try {
+            controller.close();
+          } catch {
+            // already closed
+          }
+        });
+    },
+    cancel() {
+      cleanup(); // client went away — drop the subscription + heartbeat
+    },
+  });
+
+  return new Response(stream, {
+    headers: {
+      'Content-Type': 'text/event-stream',
+      'Cache-Control': 'no-cache',
+      Connection: 'keep-alive',
+      'X-Accel-Buffering': 'no', // prod sits behind Traefik — don't buffer the stream
+    },
+  });
+}