feat(examples)+test(e2e): streaming SSR demo, proven progressive in Chromium

examples/streaming is a runnable Node server piping toStream() through Readable.fromWeb. The e2e server gains /stream, and two tests prove real streaming: shell bytes arrive over HTTP before the async hole resolves, and Chromium builds the shell DOM mid-stream, then grows the slow section into the same document without navigation. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_014NgfSjHE11oFpoSnLVKLXd
2026-09-08 18:44:52 +02:00
parent 22c5045c25
commit d22f996596
4 changed files with 134 additions and 0 deletions
@@ -7,7 +7,10 @@ import { readFile } from 'node:fs/promises'
 import { join, normalize, extname, dirname } from 'node:path'
 import { fileURLToPath } from 'node:url'

+import { Readable } from 'node:stream'
+
 import createApp from '../../examples/counter/app.js'
+import createStreamingApp from '../../examples/streaming/app.js'

 const root = normalize(join(dirname(fileURLToPath(import.meta.url)), '..', '..'))

@@ -60,6 +63,18 @@ export function startServer () {
      return
    }

+    if (url.pathname === '/stream') {
+      const delay = Number(url.searchParams.get('delay')) || 500
+      res.writeHead(200, { 'content-type': 'text/html; charset=utf-8' })
+      // padding nudges browsers to start parsing before the stream closes
+      res.write('<!doctype html>\n<html lang="en">\n<head><meta charset="utf-8"><title>choo streams</title></head>\n' + '<!-- ' + ' '.repeat(1024) + ' -->\n')
+      const body = Readable.fromWeb(createStreamingApp({ delay }).toStream('/'))
+      body.pipe(res, { end: false })
+      body.on('end', () => res.end('\n</html>'))
+      body.on('error', () => res.destroy())
+      return
+    }
+
    let pathname = decodeURIComponent(url.pathname)
    if (pathname.endsWith('/')) pathname += 'index.html'
    const file = normalize(join(root, pathname))
@@ -0,0 +1,57 @@
+// Streaming SSR, proven at two levels: raw chunk timing over HTTP, and
+// progressive DOM construction in real Chromium.
+
+import { test, before, after } from 'node:test'
+import assert from 'node:assert'
+import { chromium } from 'playwright'
+
+import { startServer } from './serve.js'
+
+const DELAY = 500
+
+let browser, srv
+
+before(async () => {
+  srv = await startServer()
+  browser = await chromium.launch()
+})
+
+after(async () => {
+  await browser?.close()
+  await srv?.close()
+})
+
+test('HTTP level: shell bytes arrive before the slow section resolves', async () => {
+  const started = performance.now()
+  const res = await fetch(`${srv.origin}/stream?delay=${DELAY}`)
+  const decoder = new TextDecoder()
+
+  let sawShellAt = null
+  let text = ''
+  for await (const chunk of res.body) {
+    text += decoder.decode(chunk, { stream: true })
+    if (sawShellAt === null && text.includes('<h1>choo streams</h1>')) {
+      sawShellAt = performance.now() - started
+      assert.ok(!text.includes('id="slow"'), 'slow section not in the early bytes')
+    }
+  }
+
+  assert.ok(sawShellAt !== null, 'shell was seen')
+  assert.ok(sawShellAt < DELAY, `shell arrived at ${sawShellAt.toFixed(0)}ms, before the ${DELAY}ms hole`)
+  assert.match(text, /id="slow"/, 'slow section arrived in the same response')
+  assert.match(text, /<\/html>/, 'document completed')
+})
+
+test('browser level: Chromium builds the shell DOM before the stream ends', async () => {
+  const page = await browser.newPage()
+  await page.goto(`${srv.origin}/stream?delay=${DELAY}`, { waitUntil: 'commit' })
+
+  // the shell must be in the DOM while the slow section is still absent
+  await page.waitForSelector('h1', { timeout: DELAY - 100 })
+  assert.strictEqual(await page.$('#slow'), null, 'slow section not parsed yet')
+
+  // then the same document grows the slow section without navigation
+  await page.waitForSelector('#slow', { timeout: DELAY * 4 })
+  assert.match(await page.textContent('#slow'), /500ms later/)
+  await page.close()
+})