Greatest: serve catalog covers from a local copy (BL-0053)

The page hotlinked ~100 AniList CDN covers per load and some failed at random.
The reader now downloads each catalog cover once (sequential, ~1/s, stops on
401/403/429, images up to 2 MB) into data/greatest-covers/ and serves it from
/api/greatest-cover with a year-long browser cache; until a copy exists the
route redirects to the catalog URL. The page also accepts the server's
relative cover URLs, so owned titles show their library cover again.
GREATEST_COVER_WARM=0 turns the downloads off (tests, offline installs).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

greatest/covers.js

@@ -0,0 +1,73 @@
+'use strict';
+
+// Local copies of the Greatest catalog's cover images. Hotlinking ~100 covers per page
+// load makes the image CDN drop some of them at random; one polite download each fixes that.
+const fs = require('node:fs');
+const path = require('node:path');
+const crypto = require('node:crypto');
+
+const TYPES = { 'image/jpeg': '.jpg', 'image/png': '.png', 'image/webp': '.webp', 'image/gif': '.gif', 'image/avif': '.avif' };
+const EXTENSIONS = new Set(Object.values(TYPES));
+const USER_AGENT = 'MangaCircus-Greatest/1.0';
+
+class GreatestCovers {
+  constructor(dir, { fetchImpl = fetch, sleep = ms => new Promise(resolve => setTimeout(resolve, ms)),
+    delayMs = 1000, maxBytes = 2 * 1024 * 1024, timeoutMs = 20000 } = {}) {
+    this.dir = path.resolve(dir);
+    Object.assign(this, { fetchImpl, sleep, delayMs, maxBytes, timeoutMs });
+    this.files = new Map(); // key -> file name
+    try {
+      for (const name of fs.readdirSync(this.dir)) {
+        const ext = path.extname(name);
+        if (EXTENSIONS.has(ext)) this.files.set(path.basename(name, ext), name);
+      }
+    } catch (error) { if (error.code !== 'ENOENT') throw error; }
+  }
+  // A hash of the URL names the file, so a changed catalog URL is fetched again.
+  version(url) { return crypto.createHash('sha256').update(String(url)).digest('hex').slice(0, 16); }
+  file(url) {
+    const name = url ? this.files.get(this.version(url)) : null;
+    return name ? path.join(this.dir, name) : null;
+  }
+  // Sequential, paced, and stops on 403/429 like every other outbound client here.
+  async warm(urls) {
+    const result = { fetched: 0, skipped: 0, failed: 0, stopped: null };
+    let requested = false;
+    for (const url of new Set(urls.filter(url => /^https:\/\/\S+$/i.test(String(url || ''))))) {
+      if (this.file(url)) { result.skipped++; continue; }
+      if (requested) await this.sleep(this.delayMs);
+      requested = true;
+      try {
+        await this.download(url);
+        result.fetched++;
+      } catch (error) {
+        if (error.stop) { result.stopped = error.message; break; }
+        result.failed++;
+      }
+    }
+    // Duplicates and repeats of stored covers count as skipped.
+    result.skipped += urls.filter(Boolean).length - new Set(urls.filter(Boolean)).size;
+    return result;
+  }
+  async download(url) {
+    const response = await this.fetchImpl(url, { headers: { 'user-agent': USER_AGENT },
+      signal: AbortSignal.timeout(this.timeoutMs) });
+    if ([401, 403, 429].includes(response.status)) throw Object.assign(new Error(`HTTP ${response.status}`), { stop: true });
+    if (!response.ok) throw new Error(`HTTP ${response.status}`);
+    const ext = TYPES[String(response.headers.get('content-type') || '').split(';')[0].trim().toLowerCase()];
+    if (!ext) throw new Error('Not an image');
+    if (Number(response.headers.get('content-length')) > this.maxBytes) throw new Error('Image too large');
+    const body = Buffer.from(await response.arrayBuffer());
+    if (!body.length || body.length > this.maxBytes) throw new Error('Image too large or empty');
+    const key = this.version(url), name = key + ext;
+    fs.mkdirSync(this.dir, { recursive: true });
+    const temp = path.join(this.dir, `.${key}.${crypto.randomBytes(4).toString('hex')}.tmp`);
+    try {
+      fs.writeFileSync(temp, body);
+      fs.renameSync(temp, path.join(this.dir, name));
+    } finally { fs.rmSync(temp, { force: true }); }
+    this.files.set(key, name);
+  }
+}
+
+module.exports = { GreatestCovers };