Route Handlers, Streaming Responses & after() Lifecycle

1// app/api/chat/route.ts
2import { NextRequest } from 'next/server';
3import { after } from 'next/server'; // Next.js 15+ API
4import { logAuditTrail } from '@/lib/audit';
5
6export async function POST(req: NextRequest) {
7  const { prompt, userId } = await req.json();
8  const startTime = Date.now();
9
10  // 1. Create a custom streaming response
11  const encoder = new TextEncoder();
12  const stream = new ReadableStream({
13    async start(controller) {
14      const words = ['Artificial', 'Intelligence', 'Streaming', 'in', 'Next.js', '15!'];
15      for (const word of words) {
16        controller.enqueue(encoder.encode(`data: ${word}\n\n`));
17        await new Promise((res) => setTimeout(res, 100)); // Simulate LLM token delay
18      }
19      controller.close();
20    },
21  });
22
23  // 2. Schedule non-blocking work with after()
24  // Executes AFTER the HTTP response has been sent to the client!
25  after(async () => {
26    const duration = Date.now() - startTime;
27    console.log(`[AUDIT] Request finished in ${duration}ms. Persisting log...`);
28    await logAuditTrail({
29      userId,
30      promptLength: prompt.length,
31      durationMs: duration,
32      timestamp: new Date(),
33    });
34  });
35
36  // 3. Return streaming Response immediately
37  return new Response(stream, {
38    headers: {
39      'Content-Type': 'text/event-stream',
40      'Cache-Control': 'no-cache',
41      Connection: 'keep-alive',
42    },
43  });
44}