feat(docs): serve Markdown to clients that ask for it - #12596
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Pull request overview
Adds Cloudflare Pages middleware-based content negotiation so clients explicitly requesting text/markdown receive the existing per-page *.md “twin”, while keeping CDN caching correct via Vary: Accept and avoiding Worker invocations for most static assets.
Changes:
- Introduces
prefersMarkdown()+isNegotiablePage()utilities (with Vitest coverage) to drive safe Accept-header negotiation. - Adds Pages middleware to rewrite negotiable page requests to their
*.mdtwin, return Markdown-formatted 404s when appropriate, and mergeAcceptintoVaryfor negotiated media types. - Adds
<link rel="alternate" type="text/markdown">in page head, and introduces_routes.jsonplus lint/format ignores for local Wrangler artifacts.
Reviewed changes
Copilot reviewed 7 out of 8 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
| src/util/acceptMarkdown.ts | Implements Accept parsing + policy for when to serve Markdown. |
| src/util/acceptMarkdown.test.ts | Unit tests covering key negotiation scenarios and asset/page detection. |
| src/components/HeadSEO.astro | Publishes the Markdown twin via an alternate link tag. |
| public/_routes.json | Limits Pages Function routing to page requests by excluding major static asset paths. |
| functions/_middleware.ts | Rewrites requests to *.md when appropriate and sets Vary: Accept on negotiated responses. |
| eslint.config.js | Ignores local .wrangler/ artifacts for linting. |
| biome.json | Excludes .wrangler/ from Biome formatting/linting. |
| .gitignore | Ignores local Wrangler build artifacts. |
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Every page already ships its Markdown source at `<path>.md`, which is what the "View as Markdown" button and `llms.txt` link to. But the convention agents reach for first is to request the page's own URL with `Accept: text/markdown` (https://acceptmarkdown.com), and that returned HTML. The site is a static build, so a Cloudflare Pages middleware is the only layer that sees request headers. It rewrites to the `.md` twin when Markdown is asked for, answers 404s in the format that was requested, and merges `Accept` into `Vary` on both variants — without it a CDN would hand whichever variant it cached first to everyone, which is the failure this is most likely to produce in production and the least likely to be noticed. The `Vary` goes on `304` responses too, since those are exactly the ones a cache is about to act on. Markdown is served only when `text/markdown` is named explicitly and not outranked by `text/html`. Browsers send `text/html,...,*/*;q=0.8`, so honouring wildcards would serve raw Markdown to every human visitor; the tests pin the real Chrome and Firefox Accept headers against that. HTML is served as the fallback only on a `404` from the `.md` route, not on anything that is merely not `ok`: `304 Not Modified` is the normal answer to a client revalidating Markdown it already holds, and treating it as a missing page answered it with HTML. Three things about adding a root `_middleware` needed care, all three verified against the real Pages runtime with `wrangler pages dev dist`: Cloudflare documents that `_redirects` are not applied to requests served by Functions, and this repository has 99 of them. `next()` does still route through the asset server, so every redirect, the `_headers` rules, the `.md` routes and the static 404 behave exactly as before. `next()` is called with an explicit request everywhere. A bare `next()` is documented as forwarding the original request, but once the middleware has asked for the Markdown twin the runtime forwards *that* request again — so `/api` and `/cli`, which are built from `src/pages/` and have no `.md`, were answered with the Markdown 404 instead of their own HTML. The test double refuses a call with no request so this cannot come back. A root middleware otherwise turns every request into a Worker invocation, assets included — roughly thirty per page view, none of which can be negotiated. `_routes.json` excludes the bundle, the search index, the OpenGraph images and the static files by name, so only page requests reach the Function. Also ignore `.wrangler/` — running the Pages runtime locally drops generated bundles there, and eslint linted them. Change-Id: I52f9d2a1c70248b1406412129a633cc3bee219de
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Every page already ships its Markdown source at
<path>.md, which is what the"View as Markdown" button and
llms.txtlink to. But the convention agentsreach for first is to request the page's own URL with
Accept: text/markdown(https://acceptmarkdown.com), and that returned HTML.
The site is a static build, so a Cloudflare Pages middleware is the only layer
that sees request headers. It rewrites to the
.mdtwin when Markdown is askedfor, answers 404s in the format that was requested, and merges
AcceptintoVaryon both variants — without it a CDN would hand whichever variant itcached first to everyone, which is the failure this is most likely to produce
in production and the least likely to be noticed. The
Varygoes on304responses too, since those are exactly the ones a cache is about to act on.
Markdown is served only when
text/markdownis named explicitly and notoutranked by
text/html. Browsers sendtext/html,...,*/*;q=0.8, so honouringwildcards would serve raw Markdown to every human visitor; the tests pin the
real Chrome and Firefox Accept headers against that.
HTML is served as the fallback only on a
404from the.mdroute, not onanything that is merely not
ok:304 Not Modifiedis the normal answer to aclient revalidating Markdown it already holds, and treating it as a missing
page answered it with HTML.
Three things about adding a root
_middlewareneeded care, all three verifiedagainst the real Pages runtime with
wrangler pages dev dist:Cloudflare documents that
_redirectsare not applied to requests served byFunctions, and this repository has 99 of them.
next()does still routethrough the asset server, so every redirect, the
_headersrules, the.mdroutes and the static 404 behave exactly as before.
next()is called with an explicit request everywhere. A barenext()isdocumented as forwarding the original request, but once the middleware has
asked for the Markdown twin the runtime forwards that request again — so
/apiand/cli, which are built fromsrc/pages/and have no.md, wereanswered with the Markdown 404 instead of their own HTML. The test double
refuses a call with no request so this cannot come back.
A root middleware otherwise turns every request into a Worker invocation,
assets included — roughly thirty per page view, none of which can be
negotiated.
_routes.jsonexcludes the bundle, the search index, theOpenGraph images and the static files by name, so only page requests reach the
Function.
Also ignore
.wrangler/— running the Pages runtime locally drops generatedbundles there, and eslint linted them.
Depends-On: #12595