1 files changed, 61 insertions, 0 deletions
diff --git a/workers/preview/src/index.ts b/workers/preview/src/index.ts
new file mode 100644
index 00000000..5c945175
--- /dev/null
+++ b/workers/preview/src/index.ts
@@ -0,0 +1,61 @@
+export interface Env { PREVIEWS: R2Bucket }
+
+const MIME: Record<string, string> = {
+  html: "text/html; charset=utf-8", css: "text/css", js: "text/javascript",
+  json: "application/json", svg: "image/svg+xml", png: "image/png", jpg: "image/jpeg",
+  gif: "image/gif", ico: "image/x-icon", txt: "text/plain; charset=utf-8",
+  xml: "application/xml", pdf: "application/pdf", woff2: "font/woff2", woff: "font/woff",
+};
+
+export function mimeFor(key: string): string {
+  const ext = key.split(".").pop() ?? "";
+  return MIME[ext] ?? "application/octet-stream";
+}
+
+export function keyFor(pathname: string): string {
+  let key = pathname.replace(/^\//, "");
+  if (key.endsWith("/") || key === "" ) key += "index.html";
+  return key;
+}
+
+export default {
+  async fetch(request: Request, env: Env): Promise<Response> {
+    const key = keyFor(new URL(request.url).pathname);
+    let obj: R2ObjectBody | null = null;
+    let resolvedKey = key;
+    try {
+      obj = await env.PREVIEWS.get(key);
+      if (!obj && !key.split("/").pop()?.includes(".")) {
+        // Extensionless directory URL with no trailing slash (e.g. /en/rolling/cli) —
+        // keyFor() only appends index.html for trailing-slash/empty paths, so probe the
+        // directory's index.html before 404ing. Check the LAST path segment only — a dot
+        // anywhere earlier (e.g. version segment "1.4" in /pr-42/en/1.4/cli) must not skip
+        // the probe for an otherwise-extensionless final segment.
+        resolvedKey = `${key}/index.html`;
+        obj = await env.PREVIEWS.get(resolvedKey);
+      }
+    } catch {
+      // Transient R2/binding error on either probe — fail closed with a controlled 503
+      // instead of letting an unhandled exception surface as a raw worker error.
+      return new Response("preview temporarily unavailable", {
+        status: 503,
+        headers: { "X-Robots-Tag": "noindex", "Cache-Control": "no-store" },
+      });
+    }
+    if (!obj) {
+      return new Response("preview not found", {
+        status: 404,
+        // no-store on the 404 too — a cached 404 would persist past the preview upload
+        headers: { "X-Robots-Tag": "noindex", "Cache-Control": "no-store" },
+      });
+    }
+    return new Response(obj.body, {
+      headers: {
+        "content-type": obj.httpMetadata?.contentType ?? mimeFor(resolvedKey),
+        "X-Robots-Tag": "noindex",
+        "Cache-Control": "no-store",
+        "X-Content-Type-Options": "nosniff",
+      },
+    });
+  },
+} satisfies ExportedHandler<Env>;