feat: Implement ETag-based conditional caching for API and HTML, add immutable caching for images, and introduce concurrency control with resizing for picture syncing.

server.js

@@ -6,27 +6,86 @@ import fs from 'fs/promises';
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = path.dirname(__filename);
 
-export function startServer() {
+export function startServer(categorySyncer) {
     const app = express();
     const PORT = process.env.SERVER_PORT || 3000;
     const HOST = process.env.SERVER_HOST || '0.0.0.0';
     const CACHE_DIR = process.env.CACHE_LOCATION || './cache';
 
-    // Serve category tree JSON
-    app.get('/api/categories', async (req, res) => {
+    // Cache for ETags and data
+    const cache = {
+        categories: { etag: null, data: null },
+        html: { etag: null, data: null }
+    };
+
+    // Function to calculate ETag for categories
+    async function updateCategoriesCache() {
         try {
             const treePath = path.join(CACHE_DIR, 'category_tree.json');
             const data = await fs.readFile(treePath, 'utf-8');
-            res.json(JSON.parse(data));
+            const crypto = await import('crypto');
+            cache.categories.etag = crypto.createHash('md5').update(data).digest('hex');
+            cache.categories.data = data;
+        } catch (err) {
+            // Silently skip if file doesn't exist yet (will be created on first sync)
+            if (err.code !== 'ENOENT') {
+                console.error('Error updating categories cache:', err);
+            }
+        }
+    }
+
+    // Function to calculate ETag for HTML
+    async function updateHtmlCache() {
+        try {
+            const htmlPath = path.join(__dirname, 'index.html');
+            const data = await fs.readFile(htmlPath, 'utf-8');
+            const crypto = await import('crypto');
+            cache.html.etag = crypto.createHash('md5').update(data).digest('hex');
+            cache.html.data = data;
+        } catch (err) {
+            console.error('Error updating HTML cache:', err);
+        }
+    }
+
+    // Initialize caches on startup
+    updateHtmlCache();
+    updateCategoriesCache();
+
+    // Update categories cache when sync completes
+    if (categorySyncer) {
+        categorySyncer.on('synced', ({ changed }) => {
+            if (changed) {
+                updateCategoriesCache();
+            }
+        });
+    }
+
+    // Serve category tree JSON (with ETag for conditional caching)
+    app.get('/api/categories', async (req, res) => {
+        try {
+            // Check if client has cached version
+            if (req.headers['if-none-match'] === cache.categories.etag) {
+                return res.status(304).end(); // Not Modified
+            }
+
+            // Set cache headers with ETag
+            res.set('Cache-Control', 'public, max-age=60, must-revalidate');
+            res.set('ETag', cache.categories.etag);
+
+            res.json(JSON.parse(cache.categories.data));
         } catch (err) {
             res.status(500).json({ error: 'Failed to load category tree' });
         }
     });
 
-    // Serve category images
+    // Serve category images (long cache - images rarely change)
     app.get('/img/cat/:id.avif', (req, res) => {
         const { id } = req.params;
         const imagePath = path.join(CACHE_DIR, 'img', 'categories', `${id}.avif`);
+
+        // Cache images for 1 year (immutable content)
+        res.set('Cache-Control', 'public, max-age=31536000, immutable');
+
         res.sendFile(path.resolve(imagePath), (err) => {
             if (err) {
                 res.status(404).send('Image not found');
@@ -34,16 +93,24 @@ export function startServer() {
         });
     });
 
-    // Serve index.html
-    app.get('/', (req, res) => {
-        const htmlPath = path.join(__dirname, 'index.html');
-        console.log('Attempting to serve:', htmlPath);
-        res.sendFile(htmlPath, (err) => {
-            if (err) {
-                console.error('Error serving index.html:', err);
-                res.status(500).send('Error loading page');
+    // Serve index.html (with ETag for conditional caching)
+    app.get('/', async (req, res) => {
+        try {
+            // Check if client has cached version
+            if (req.headers['if-none-match'] === cache.html.etag) {
+                return res.status(304).end(); // Not Modified
             }
-        });
+
+            // Set cache headers with ETag
+            res.set('Cache-Control', 'public, max-age=300, must-revalidate');
+            res.set('ETag', cache.html.etag);
+            res.set('Content-Type', 'text/html');
+
+            res.send(cache.html.data);
+        } catch (err) {
+            console.error('Error serving index.html:', err);
+            res.status(500).send('Error loading page');
+        }
     });
 
     app.listen(PORT, HOST, () => {