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Fix chunk buffering for server components #34474

Merged
merged 4 commits into from Feb 17, 2022
Merged

Fix chunk buffering for server components #34474

merged 4 commits into from Feb 17, 2022

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shuding
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@shuding shuding commented Feb 17, 2022

When testing vercel/server-components-notes-demo#11, we've observed some weird issues that the initial chunk (the "shell") is sometimes broken, and mixed with the data stream. After some testing I confirmed that our buffering (createBufferedTransformStream) is working as we expected: the first chunk it queues is the correct and complete shell. However it's impossible to inject extra things inside a single data chunk. With some deeper investigation it turned out to be something in the underlying Web Stream implementation in the platform — it has a fixed queue size, probably using ByteLengthQueuingStrategy, which makes larger chunks (~8,192B) being splitted into smaller ones. Since we pass everything through two TransformStreams, our buffered shell is chunkenized again.

As described in the code comment, the safest and easiest way to address this is to put the buffering strategy just before merging the data stream.

The issue cannot be reproduce with this fix applied: https://server-components-notes-demo-shuding1.vercel.app. However, it seems not possible to reproduce in a local environment.

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@ijjk ijjk added created-by: Next.js team type: next labels Feb 17, 2022
huozhi
huozhi approved these changes Feb 17, 2022
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@ijjk ijjk commented Feb 17, 2022

Stats from current PR

Default Build
General Overall increase ⚠️
vercel/next.js canary shuding/next.js shu/f3f5 Change
buildDuration 20.1s 20s -61ms
buildDurationCached 7.7s 7.9s ⚠️ +197ms
nodeModulesSize 359 MB 359 MB ⚠️ +692 B
Page Load Tests Overall increase ✓
vercel/next.js canary shuding/next.js shu/f3f5 Change
/ failed reqs 0 0
/ total time (seconds) 4.285 4.373 ⚠️ +0.09
/ avg req/sec 583.38 571.7 ⚠️ -11.68
/error-in-render failed reqs 0 0
/error-in-render total time (seconds) 2.153 2.126 -0.03
/error-in-render avg req/sec 1161.15 1176.1 +14.95
Client Bundles (main, webpack, commons)
vercel/next.js canary shuding/next.js shu/f3f5 Change
450.HASH.js gzip 179 B 179 B
framework-HASH.js gzip 42 kB 42 kB
main-HASH.js gzip 27.9 kB 27.9 kB
webpack-HASH.js gzip 1.44 kB 1.44 kB
Overall change 71.6 kB 71.6 kB
Legacy Client Bundles (polyfills)
vercel/next.js canary shuding/next.js shu/f3f5 Change
polyfills-HASH.js gzip 31 kB 31 kB
Overall change 31 kB 31 kB
Client Pages
vercel/next.js canary shuding/next.js shu/f3f5 Change
_app-HASH.js gzip 1.36 kB 1.36 kB
_error-HASH.js gzip 194 B 194 B
amp-HASH.js gzip 312 B 312 B
css-HASH.js gzip 326 B 326 B
dynamic-HASH.js gzip 2.57 kB 2.57 kB
head-HASH.js gzip 350 B 350 B
hooks-HASH.js gzip 919 B 919 B
image-HASH.js gzip 5.05 kB 5.05 kB
index-HASH.js gzip 263 B 263 B
link-HASH.js gzip 2.26 kB 2.26 kB
routerDirect..HASH.js gzip 321 B 321 B
script-HASH.js gzip 383 B 383 B
withRouter-HASH.js gzip 318 B 318 B
85e02e95b279..7e3.css gzip 107 B 107 B
Overall change 14.7 kB 14.7 kB
Client Build Manifests
vercel/next.js canary shuding/next.js shu/f3f5 Change
_buildManifest.js gzip 460 B 460 B
Overall change 460 B 460 B
Rendered Page Sizes
vercel/next.js canary shuding/next.js shu/f3f5 Change
index.html gzip 531 B 531 B
link.html gzip 544 B 544 B
withRouter.html gzip 526 B 526 B
Overall change 1.6 kB 1.6 kB

Default Build with SWC (Decrease detected ✓)
General Overall increase ⚠️
vercel/next.js canary shuding/next.js shu/f3f5 Change
buildDuration 24.8s 25.1s ⚠️ +375ms
buildDurationCached 7.7s 7.7s ⚠️ +46ms
nodeModulesSize 359 MB 359 MB ⚠️ +692 B
Page Load Tests Overall decrease ⚠️
vercel/next.js canary shuding/next.js shu/f3f5 Change
/ failed reqs 0 0
/ total time (seconds) 4.373 4.507 ⚠️ +0.13
/ avg req/sec 571.73 554.7 ⚠️ -17.03
/error-in-render failed reqs 0 0
/error-in-render total time (seconds) 2.169 2.218 ⚠️ +0.05
/error-in-render avg req/sec 1152.5 1126.96 ⚠️ -25.54
Client Bundles (main, webpack, commons)
vercel/next.js canary shuding/next.js shu/f3f5 Change
450.HASH.js gzip 179 B 179 B
framework-HASH.js gzip 42.1 kB 42.1 kB
main-HASH.js gzip 28 kB 28 kB
webpack-HASH.js gzip 1.44 kB 1.44 kB
Overall change 71.7 kB 71.7 kB
Legacy Client Bundles (polyfills)
vercel/next.js canary shuding/next.js shu/f3f5 Change
polyfills-HASH.js gzip 31 kB 31 kB
Overall change 31 kB 31 kB
Client Pages
vercel/next.js canary shuding/next.js shu/f3f5 Change
_app-HASH.js gzip 1.35 kB 1.35 kB
_error-HASH.js gzip 180 B 180 B
amp-HASH.js gzip 305 B 305 B
css-HASH.js gzip 321 B 321 B
dynamic-HASH.js gzip 2.56 kB 2.56 kB
head-HASH.js gzip 342 B 342 B
hooks-HASH.js gzip 911 B 911 B
image-HASH.js gzip 5.08 kB 5.08 kB
index-HASH.js gzip 256 B 256 B
link-HASH.js gzip 2.28 kB 2.28 kB
routerDirect..HASH.js gzip 314 B 314 B
script-HASH.js gzip 375 B 375 B
withRouter-HASH.js gzip 309 B 309 B
85e02e95b279..7e3.css gzip 107 B 107 B
Overall change 14.7 kB 14.7 kB
Client Build Manifests
vercel/next.js canary shuding/next.js shu/f3f5 Change
_buildManifest.js gzip 459 B 459 B
Overall change 459 B 459 B
Rendered Page Sizes
vercel/next.js canary shuding/next.js shu/f3f5 Change
index.html gzip 534 B 534 B
link.html gzip 547 B 547 B
withRouter.html gzip 528 B 528 B
Overall change 1.61 kB 1.61 kB
Commit: 717636d

styfle
styfle approved these changes Feb 17, 2022
ijjk
ijjk approved these changes Feb 17, 2022
@ijjk ijjk merged commit d4d79b2 into vercel:canary Feb 17, 2022
37 of 39 checks passed
@shuding shuding deleted the shu/f3f5 branch Feb 17, 2022
@huozhi huozhi mentioned this pull request Mar 9, 2022
kodiakhq bot pushed a commit that referenced this issue Mar 9, 2022
Only happened with SSR without suspense case

Similar reason to #34474, the prefix (script parts) might be flushed during the render stream causing bad HTML. Use the same tricky to delay the prefix flushing

#### Expected
```html
<div>content</div> <!-- render stream --> 
<script>...</script> <!-- prefix --> 
```


#### Observed
```html
<!-- prefix choked the render stream --> 
<div <script>...</script> >content</div>
```


Test sample:
https://next-react-server-components-r5xocii9r-huozhi.vercel.app/ssr
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4 participants