Answer stability round 1: 1 🔴, 0 🟡 (0 misread); share no page

CHANGELOG.md

@@ -15,10 +15,9 @@ together.
 ### Pages are not kept by a shared cache
 
 Every page and JSON response now carries `Cache-Control: private, no-store`, so a cache or reverse
-proxy in front of Plainpages can't store a signed-in page and serve it to the next visitor. The
-built-in landing `/` is shared-cacheable (`public, max-age=0, s-maxage=60`) for a signed-out visitor
-who already holds the CSRF cookie. A plugin route whose page is the same for everyone sets its own
-`cache-control` through `RouteResult.headers`; assets are unchanged.
+proxy in front of Plainpages can't store a signed-in page and serve it to the next visitor. A route
+whose page is the same for everyone can still set its own `cache-control` through
+`RouteResult.headers`; assets are unchanged.
 
 ## 0.4.0
 

src/http/app.test.ts

@@ -284,27 +284,23 @@ test("every response carries the security headers; HSTS follows SECURE_COOKIES",
   assert.match(res.headers.get("strict-transport-security") ?? "", /max-age=\d+/);
 });
 
-test("Cache-Control: every host response is private, no-store; only the anonymous built-in landing may be shared-cached", async (t) => {
+test("Cache-Control: pages and JSON are private, no-store unless the route sets its own; assets are left alone", async (t) => {
   const NO_STORE = "private, no-store";
   const csrf = (await fetch(base + "/")).headers.get("set-cookie")?.split(";")[0] ?? "";
   assert.match(csrf, new RegExp(`^${CSRF_COOKIE}=`));
 
-  // A first visit mints a per-visitor cookie, so that response must not be shared.
+  // The signed-out landing is no-store as well: it and the signed-in page share one URL.
   assert.equal((await fetch(base + "/")).headers.get("cache-control"), NO_STORE);
-  // The same page for an anonymous visitor who already holds the cookie is identical for all of them.
-  assert.equal((await fetch(base + "/", { headers: { cookie: csrf } })).headers.get("cache-control"), "public, max-age=0, s-maxage=60");
-  assert.equal((await fetch(base + "/", { headers: { cookie: csrf }, method: "HEAD" })).headers.get("cache-control"), "public, max-age=0, s-maxage=60");
-  // Signed in, the same URL carries that user's menu and sign-out form.
+  assert.equal((await fetch(base + "/", { headers: { cookie: csrf } })).headers.get("cache-control"), NO_STORE);
+  assert.equal((await fetch(base + "/", { headers: { cookie: csrf }, method: "HEAD" })).headers.get("cache-control"), NO_STORE);
   assert.equal((await fetch(base + "/", { headers: { cookie: `${csrf}; ${session()}` } })).headers.get("cache-control"), NO_STORE);
 
   assert.equal((await fetch(base + "/dashboard", { headers: { cookie: session() } })).headers.get("cache-control"), NO_STORE);
   assert.equal((await fetch(base + "/dashboard", { redirect: "manual" })).headers.get("cache-control"), NO_STORE); // sign-in bounce
   assert.equal((await fetch(base + "/nope", { headers: { cookie: csrf } })).headers.get("cache-control"), NO_STORE); // 404
-  // An asset is the same bytes for everyone; its caching is not this header's job.
   assert.equal((await fetch(base + "/public/css/styles.css")).headers.get("cache-control"), null);
 
-  // A plugin's pages and JSON default to no-store too, and a route that is the same for everyone opts in itself.
-  const shared: Plugin = {
+  const demo: Plugin = {
     apiVersion: "1.0.0",
     home: () => ({ html: "<p>plugin home</p>" }),
     id: "demo",
@@ -314,9 +310,9 @@ test("Cache-Control: every host response is private, no-store; only the anonymou
       { handler: () => ({ json: { ok: true } }), method: "GET", path: "/data", public: true },
     ],
   };
-  const url = await startApp(t, [shared]);
+  const url = await startApp(t, [demo]);
   for (const path of ["/demo/open", "/demo/data", "/"]) {
-    assert.equal((await fetch(url + path, { headers: { cookie: csrf } })).headers.get("cache-control"), NO_STORE, path);
+    assert.equal((await fetch(url + path)).headers.get("cache-control"), NO_STORE, path);
   }
   assert.equal((await fetch(url + "/demo/same")).headers.get("cache-control"), "public, max-age=600");
 });

src/http/app.ts

@@ -36,9 +36,7 @@ import { localPath } from "./safe-url.ts";
 import { routePublic, serveStatic } from "./static.ts";
 import { renderPluginView } from "../plugin-host/view-resolver.ts";
 
-// max-age=0 keeps a browser from showing a signed-out page after sign-in; only a shared cache keeps it.
 const NO_STORE = "private, no-store";
-const SHARED_PAGE = "public, max-age=0, s-maxage=60";
 
 const rootDir = join(dirname(fileURLToPath(import.meta.url)), "..", "..");
 
@@ -155,10 +153,7 @@ export function createApp(options: AppOptions = {}): Server {
       await sendResult(ctx.res, result, pluginViewsFor(pluginCtx, homePlugin.id), pluginCtx.localeHref);
       return null;
     }
-    // Shared only when nothing in the page or its headers belongs to this visitor: no user, and no
-    // Set-Cookie (a fresh CSRF cookie is per-visitor).
-    const sharable = !ctx.user && !ctx.res.hasHeader("set-cookie");
-    return { data: { chrome: ctx.chrome, user: ctx.user }, ...(sharable ? { headers: { "cache-control": SHARED_PAGE } } : {}), view: "home" };
+    return { data: { chrome: ctx.chrome, user: ctx.user }, view: "home" };
   };
 
   // "/dashboard", gated to a signed-in user. A plugin may own it via `dashboard`; else the built-in
@@ -210,9 +205,10 @@ export function createApp(options: AppOptions = {}): Server {
       // A cache in front of us must key on the language. Set after the static branch: an asset is
       // the same bytes in every language, and a Vary there fragments its entry per raw header.
       res.setHeader("vary", "accept-language");
-      // Fail closed: a cache in front of us must not keep a page that may carry a user's data. A
-      // response that is the same for everyone opts in through its own headers (serveHome below, or
-      // a plugin's RouteResult.headers).
+      // Fail closed: a cache in front of us must not keep a page that may carry a user's data. Not
+      // even the signed-out `/` is shared: it and the signed-in page have one URL, and a cache keyed
+      // on URL and Accept-Language would hand the signed-out one to a signed-in visitor. A route that
+      // is the same for everyone sets its own value in RouteResult.headers; the host doesn't police it.
       res.setHeader("cache-control", NO_STORE);
 
       // Canonical host (APP_URL): send an off-host visitor to the configured origin so the browser,