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ensure mpa navigations to the same URL work after restoring from bfcache #63155

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ztanner
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@ztanner ztanner commented Mar 11, 2024

What

When triggering an MPA navigation (also commonly referred to as a "hard navigation"), and then restoring the previous page via the browser's bfcache, subsequent requests to the same link wouldn't navigate until reloading the page or performing a different navigation.

Why

MPA navigations in app router are handled in a fairly subtle way: the router state is updated with an indication that an external URL was clicked, and once the router sees the pending navigation, it kicks off a location.replace or location.push with the specified URL in render. The router then suspends indefinitely to prevent committing the render. However, the router will only make the replace/push request if there's not already a pending navigation to that same URL.

The pending check is needed to avoid continuously calling push/replace when unrelated router state changes occur (for example, if I hover over a link and trigger a prefetch action and the router re-renders, it shouldn't make another location.push call to the same URL that's pending)

However, the source of the bug is that the variable that holds this pending state is also restored by the browser's cache, since it takes a snapshot prior to exiting the page. This means that when clicking the browser back button, pendingMpaPath would still be set to the URL we just came from. When clicking the link again, it would see that the requested URL is the same as the pending URL, and not perform any history actions.

How

This clears the pending value when the router is restored from bfcache.

slack x-ref

Closes NEXT-2781
Closes NEXT-2776

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ztanner commented Mar 11, 2024

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ijjk commented Mar 11, 2024

Stats from current PR

Default Build (Increase detected ⚠️)
General Overall increase ⚠️
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
buildDuration 14s 14.1s N/A
buildDurationCached 7.5s 6.5s N/A
nodeModulesSize 198 MB 198 MB ⚠️ +1.68 kB
nextStartRea..uration (ms) 447ms 436ms N/A
Client Bundles (main, webpack)
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
2453-HASH.js gzip 30.5 kB 30.5 kB N/A
3304.HASH.js gzip 181 B 181 B
3f784ff6-HASH.js gzip 53.7 kB 53.7 kB N/A
8299-HASH.js gzip 5.04 kB 5.04 kB N/A
framework-HASH.js gzip 45.2 kB 45.2 kB
main-app-HASH.js gzip 242 B 242 B
main-HASH.js gzip 32.2 kB 32.2 kB N/A
webpack-HASH.js gzip 1.68 kB 1.68 kB N/A
Overall change 45.6 kB 45.6 kB
Legacy Client Bundles (polyfills)
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
polyfills-HASH.js gzip 31 kB 31 kB
Overall change 31 kB 31 kB
Client Pages
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
_app-HASH.js gzip 196 B 197 B N/A
_error-HASH.js gzip 184 B 184 B
amp-HASH.js gzip 505 B 505 B
css-HASH.js gzip 324 B 325 B N/A
dynamic-HASH.js gzip 2.5 kB 2.5 kB N/A
edge-ssr-HASH.js gzip 258 B 258 B
head-HASH.js gzip 352 B 352 B
hooks-HASH.js gzip 370 B 371 B N/A
image-HASH.js gzip 4.21 kB 4.21 kB
index-HASH.js gzip 259 B 259 B
link-HASH.js gzip 2.67 kB 2.67 kB N/A
routerDirect..HASH.js gzip 314 B 312 B N/A
script-HASH.js gzip 386 B 386 B
withRouter-HASH.js gzip 309 B 309 B
1afbb74e6ecf..834.css gzip 106 B 106 B
Overall change 6.57 kB 6.57 kB
Client Build Manifests
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
_buildManifest.js gzip 481 B 484 B N/A
Overall change 0 B 0 B
Rendered Page Sizes
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
index.html gzip 530 B 528 B N/A
link.html gzip 540 B 540 B
withRouter.html gzip 524 B 522 B N/A
Overall change 540 B 540 B
Edge SSR bundle Size
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
edge-ssr.js gzip 95.1 kB 95.1 kB N/A
page.js gzip 3.06 kB 3.07 kB N/A
Overall change 0 B 0 B
Middleware size
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
middleware-b..fest.js gzip 628 B 624 B N/A
middleware-r..fest.js gzip 151 B 151 B
middleware.js gzip 25.5 kB 25.5 kB N/A
edge-runtime..pack.js gzip 839 B 839 B
Overall change 990 B 990 B
Next Runtimes
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
app-page-exp...dev.js gzip 171 kB 171 kB
app-page-exp..prod.js gzip 96.5 kB 96.5 kB
app-page-tur..prod.js gzip 98.3 kB 98.3 kB
app-page-tur..prod.js gzip 92.7 kB 92.7 kB
app-page.run...dev.js gzip 149 kB 149 kB
app-page.run..prod.js gzip 91.2 kB 91.2 kB
app-route-ex...dev.js gzip 21.3 kB 21.3 kB
app-route-ex..prod.js gzip 15 kB 15 kB
app-route-tu..prod.js gzip 15 kB 15 kB
app-route-tu..prod.js gzip 14.8 kB 14.8 kB
app-route.ru...dev.js gzip 21 kB 21 kB
app-route.ru..prod.js gzip 14.8 kB 14.8 kB
pages-api-tu..prod.js gzip 9.52 kB 9.52 kB
pages-api.ru...dev.js gzip 9.8 kB 9.8 kB
pages-api.ru..prod.js gzip 9.52 kB 9.52 kB
pages-turbo...prod.js gzip 22.3 kB 22.3 kB
pages.runtim...dev.js gzip 22.9 kB 22.9 kB
pages.runtim..prod.js gzip 22.3 kB 22.3 kB
server.runti..prod.js gzip 50.5 kB 50.5 kB
Overall change 948 kB 948 kB
build cache Overall increase ⚠️
vercel/next.js canary vercel/next.js 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache Change
0.pack gzip 1.56 MB 1.56 MB ⚠️ +500 B
index.pack gzip 105 kB 105 kB N/A
Overall change 1.56 MB 1.56 MB ⚠️ +500 B
Diff details
Diff for middleware.js

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Commit: a9cb95f

@ztanner ztanner marked this pull request as ready for review March 11, 2024 21:39
@ztanner ztanner merged commit 465109e into canary Mar 11, 2024
75 checks passed
@ztanner ztanner deleted the 03-11-ensure_mpa_navigations_to_the_same_URL_work_after_restoring_from_bfcache branch March 11, 2024 21:55
ztanner added a commit that referenced this pull request Mar 18, 2024
…che (#63155)

### What
When triggering an MPA navigation (also commonly referred to as a "hard
navigation"), and then restoring the previous page via the browser's
bfcache, subsequent requests to the same link wouldn't navigate until
reloading the page or performing a different navigation.

### Why
MPA navigations in app router are handled in a fairly unconventional
way: the router state is updated with an indication that an external URL
was clicked, and once the router sees the pending navigation, it kicks
off a `location.replace` or `location.push` with the specified URL **in
render**. The router then suspends indefinitely to prevent committing
the render. However, the router will only make the `replace`/`push`
request if there's not already a pending navigation to that same URL.

The pending check is needed to avoid continuously calling
`push`/`replace` when unrelated router state changes occur (for example,
if I hover over a link and trigger a prefetch action and the router
re-renders, it shouldn't make another `location.push` call to the same
URL that's pending)

However, the source of the bug is that the variable that holds this
pending state is also restored by the browser's cache, since it takes a
snapshot prior to exiting the page. This means that when clicking the
browser back button, `pendingMpaPath` would still be set to the URL we
just came from. When clicking the link again, it would see that the
requested URL is the same as the pending URL, and not perform any
history actions.

### How
This clears the pending value when the router is restored from bfcache.

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Closes NEXT-2781
Closes NEXT-2776
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