fix: image optimizer hangs when invalid image is requested

[kyliau]

When an invalid image is requested, the 'finish' event is never triggered,
which ultimately leads to a 504 Gateway Timeout error.

This is fixed by invoking the 'callback' in _write().

fix #33441

Bug

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• 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
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Documentation / Examples

• Make sure the linting passes by running yarn lint

[styfle]

Suggested change

	callback()
	if (callback) callback()

The docs mention that encoding and callback are both optional parameters so best to check it exists

[kyliau]

I think the two parameters are optional when calling write()
https://nodejs.org/docs/latest-v16.x/api/stream.html#writablewritechunk-encoding-callback
but not when calling _write()
https://nodejs.org/docs/latest-v16.x/api/stream.html#writable_writechunk-encoding-callback

[styfle]

Great work, thanks! 🎉

[kyliau]

also, FWIW, the following test should have failed on CI but apparently it does not.
On my local machine the test hangs.

next.js/test/integration/image-optimizer/test/index.test.js

Lines 774 to 780 in eaf680d

	it("should error if the resource isn't a valid image", async () => {
	const query = { url: '/test.txt', w, q: 80 }
	const opts = { headers: { accept: 'image/webp' } }
	const res = await fetchViaHTTP(appPort, '/_next/image', query, opts)
	expect(res.status).toBe(400)
	expect(await res.text()).toBe("The requested resource isn't a valid image.")
	})

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
buildDuration	12.5s	12.7s	⚠️ +174ms
buildDurationCached	3.4s	3.3s	-27ms
nodeModulesSize	356 MB	356 MB	⚠️ +589 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.912	2.94	⚠️ +0.03
/ avg req/sec	858.39	850.36	⚠️ -8.03
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.381	1.367	-0.01
/error-in-render avg req/sec	1810.45	1829.21	+18.76

Client Bundles (main, webpack, commons)

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	27.2 kB	27.2 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71 kB	71 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
_app-HASH.js gzip	1.37 kB	1.37 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	2.37 kB	2.37 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	919 B	919 B	✓
image-HASH.js gzip	4.94 kB	4.94 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.19 kB	2.19 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	14.4 kB	14.4 kB	✓

Client Build Manifests

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
index.html gzip	531 B	531 B	✓
link.html gzip	545 B	545 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	kyliau/next.js image-optimizer	Change
buildDuration	16s	16s	⚠️ +19ms
buildDurationCached	3.4s	3.3s	-44ms
nodeModulesSize	356 MB	356 MB	⚠️ +589 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.944	2.947	0
/ avg req/sec	849.1	848.33	⚠️ -0.77
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.334	1.351	⚠️ +0.02
/error-in-render avg req/sec	1874.38	1850.98	⚠️ -23.4

Client Bundles (main, webpack, commons)

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	27.3 kB	27.3 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.3 kB	71.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	kyliau/next.js image-optimizer	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	2.36 kB	2.36 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	911 B	911 B	✓
image-HASH.js gzip	4.97 kB	4.97 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.21 kB	2.21 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	14.3 kB	14.3 kB	✓

Client Build Manifests

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	kyliau/next.js image-optimizer	Change
index.html gzip	531 B	531 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: a5cd3f5