javascript 54 lines · 9 steps

Streaming a CSV export in a Next.js route

A Next.js GET handler streams database rows into a downloadable CSV without buffering the whole result in memory.

Explained by highlit
Next.js Advanced streaming csv readablestream backpressure route-handler
1import { NextResponse } from 'next/server';
2import { db } from '@/lib/db';
3 
4function csvCell(value) {
5 if (value == null) return '';
6 const str = String(value);
7 return /[",\n]/.test(str) ? `"${str.replace(/"/g, '""')}"` : str;
8}
9 
10export async function GET(request) {
11 const { searchParams } = new URL(request.url);
12 const status = searchParams.get('status') ?? 'active';
13 const since = searchParams.get('since');
14 
15 const cursor = db.orders.stream({
16 where: {
17 status,
18 ...(since ? { createdAt: { gte: new Date(since) } } : {}),
19 },
20 orderBy: { createdAt: 'asc' },
21 });
22 
23 const columns = ['id', 'customerEmail', 'total', 'status', 'createdAt'];
24 const encoder = new TextEncoder();
25 
26 const stream = new ReadableStream({
27 async start(controller) {
28 controller.enqueue(encoder.encode(columns.join(',') + '\n'));
29 try {
30 for await (const order of cursor) {
31 const row = columns.map((col) => csvCell(order[col])).join(',');
32 controller.enqueue(encoder.encode(row + '\n'));
33 }
34 } catch (err) {
35 controller.error(err);
36 return;
37 }
38 controller.close();
39 },
40 cancel() {
41 cursor.return?.();
42 },
43 });
44 
45 const filename = `orders-${status}-${new Date().toISOString().slice(0, 10)}.csv`;
46 
47 return new NextResponse(stream, {
48 headers: {
49 'Content-Type': 'text/csv; charset=utf-8',
50 'Content-Disposition': `attachment; filename="${filename}"`,
51 'Cache-Control': 'no-store',
52 },
53 });
54}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Streaming rows one at a time keeps memory flat no matter how large the export grows.
  2. 2CSV cells must escape quotes, commas, and newlines to stay parseable.
  3. 3A stream's cancel hook lets you release the database cursor when the client disconnects.

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