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#179: negotiate the SPA shell's lang attribute in nginx
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Browse Source 
`apps/web/index.html` carries a hard `lang="en"`. The app corrects it at
runtime (#163), but nginx answers every SPA route with that same file, so a
crawler or a no-JS visit — `/public/...` on prod is exactly that — saw `en`
for German content, permanently. WCAG 3.1.1 is about the delivered document,
not the one JavaScript later fixes.

nginx-only, no backend involved: a `map` on `Accept-Language` and a
`sub_filter` in the index.html path. Only the FIRST tag decides, which is
what "the browser's preferred language" means and mirrors #163 — `de-CH`
counts as German, `en-US,de` does not.

`Vary: Accept-Language` is new. The response now genuinely depends on a
request header, and without it a shared cache could hand one language's copy
to the other. Everything else in the location is untouched: same CSP, same
`Cache-Control: no-cache`, same `nosniff`.

The known limit is documented in the config rather than worked around: nginx
cannot read `instance.defaultLocale`, so an unlisted or absent
Accept-Language yields `en` even on a German instance. For public content
that is not the authoritative rendering anyway — the api's server shell
(`/api/v1/public/...`) already renders those with the instance locale.

Verified against a real nginx 1.27 (the image the stage runs) with the
config mounted as-is: `de-DE,de;q=0.9,en;q=0.8` and `de` yield `lang="de"`;
`en-US,en;q=0.9`, `en-US,en;q=0.9,de;q=0.8`, `fr-FR,fr` and a request with no
header yield `lang="en"`; an SPA route (`/public/teich/seite`) negotiates the
same way; the gzipped response is rewritten too, and a JavaScript asset comes
through byte-identical.
This commit is contained in:
Claude Opus 5 2026-08-01 19:18:24 +02:00
parent 6377faf332
commit 8752cf0c5a
1 changed files with 31 additions and 0 deletions
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31
apps/web/nginx.conf
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@ -1,3 +1,23 @@
# The SPA shell's `lang` attribute, negotiated from the request (issue #179,
# WCAG 3.1.1). `apps/web/index.html` is a static file with a hard `lang="en"`;
# the app corrects it at runtime (#163), but a crawler or a no-JS visit of an
# SPA route — which nginx answers with index.html — would see `en` forever,
# even for German content.
#
# Only the FIRST tag of Accept-Language decides, which is what "the browser's
# preferred language" means and mirrors #163's semantics. `de-CH` counts as
# German; `en-US,de` does not, because that visitor asked for English first.
#
# Known limit, documented rather than worked around: nginx does not know
# `instance.defaultLocale` from the database, so a visitor with no (or an
# unlisted) Accept-Language gets `en` even on a German instance. For PUBLIC
# content that is not the authoritative rendering anyway — the api's server
# shell (`/api/v1/public/...`) renders those with the instance locale.
map $http_accept_language $spa_lang {
default en;
~*^de de;
}
# SPA serving: static assets with long-lived caching, everything else
# falls back to index.html (client-side routing).
server {
@ -34,6 +54,17 @@ server {
# zero-third-party-request guarantee (security.md) is unaffected.
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; font-src 'self' data:; img-src 'self' data: blob:; connect-src 'self'; worker-src 'self'; manifest-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'self'" always;
add_header X-Content-Type-Options "nosniff" always;
# The shell's language (issue #179). Only the html document is
# rewritten, and only its first match — `<html lang="en">` is the
# first and only occurrence in index.html. Everything else this
# location serves passes through untouched.
sub_filter_types text/html;
sub_filter_once on;
sub_filter 'lang="en"' 'lang="$spa_lang"';
# The response now depends on a request header, so shared caches must
# not serve one language's copy to the other. This location is
# `no-cache` anyway; the header states the dependency correctly.
add_header Vary "Accept-Language" always;
try_files $uri /index.html;
}
}