Improve error handling in the SSR middleware

[shuding]

This PR improves error handling in the SSR middleware. Previously the response was sent out synchronously, and and errors were silently swallowed. There was no .catch for renderToHTML. This changes the middleware to be asynchronous, which waits until the initial Document to be rendered correctly and then starts the streaming.

With this change we can also send correct status code when there're immediate errors before Fizz.

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running yarn lint

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall decrease ✓

	vercel/next.js canary	shuding/next.js shu/b1ee	Change
buildDuration	21.3s	21.7s	⚠️ +405ms
buildDurationCached	4.2s	4.5s	⚠️ +230ms
nodeModulesSize	332 MB	332 MB	-20 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	shuding/next.js shu/b1ee	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.657	3.922	⚠️ +0.27
/ avg req/sec	683.71	637.47	⚠️ -46.24
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.887	2.211	⚠️ +0.32
/error-in-render avg req/sec	1324.53	1130.47	⚠️ -194.06

Client Bundles (main, webpack, commons)

	vercel/next.js canary	shuding/next.js shu/b1ee	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	28 kB	28 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	71.9 kB	71.9 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	shuding/next.js shu/b1ee	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/b1ee	Change
_app-HASH.js gzip	1.23 kB	1.23 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	635 B	635 B	✓
image-HASH.js gzip	4.44 kB	4.44 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	1.87 kB	1.87 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	✓
334f979574ae..6f4.css gzip	106 B	106 B	✓
Overall change	13.1 kB	13.1 kB	✓

Client Build Manifests

	vercel/next.js canary	shuding/next.js shu/b1ee	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/b1ee	Change
index.html gzip	522 B	522 B	✓
link.html gzip	535 B	535 B	✓
withRouter.html gzip	515 B	515 B	✓
Overall change	1.57 kB	1.57 kB	✓

---

Default Build with SWC (Increase detected ⚠️)

General Overall decrease ✓

	vercel/next.js canary	shuding/next.js shu/b1ee	Change
buildDuration	23s	22.8s	-241ms
buildDurationCached	4.1s	4.1s	⚠️ +20ms
nodeModulesSize	332 MB	332 MB	-20 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	shuding/next.js shu/b1ee	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.737	3.597	-0.14
/ avg req/sec	668.92	695.03	+26.11
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.969	1.922	-0.05
/error-in-render avg req/sec	1269.39	1300.87	+31.48

Client Bundles (main, webpack, commons)

	vercel/next.js canary	shuding/next.js shu/b1ee	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.2 kB	28.2 kB	✓
webpack-HASH.js gzip	1.43 kB	1.43 kB	✓
Overall change	72.1 kB	72.1 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	shuding/next.js shu/b1ee	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/b1ee	Change
_app-HASH.js gzip	1.22 kB	1.22 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	2.38 kB	2.38 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	622 B	622 B	✓
image-HASH.js gzip	4.46 kB	4.46 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	1.91 kB	1.91 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	✓
334f979574ae..6f4.css gzip	106 B	106 B	✓
Overall change	13.1 kB	13.1 kB	✓

Client Build Manifests

	vercel/next.js canary	shuding/next.js shu/b1ee	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/b1ee	Change
index.html gzip	521 B	521 B	✓
link.html gzip	534 B	534 B	✓
withRouter.html gzip	515 B	515 B	✓
Overall change	1.57 kB	1.57 kB	✓

Commit: a4c2934