Add in-process server module with setState entry point

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

desktop-client/server.js

@@ -0,0 +1,82 @@
+const express = require('express');
+const http = require('http');
+const { WebSocketServer } = require('ws');
+const { initialState, mergeState } = require('./state');
+
+/**
+ * Start the now-playing server.
+ *
+ * @param {Object} opts
+ * @param {number} opts.port         Port to listen on (e.g. 9095).
+ * @param {string} [opts.overlayDir] Absolute path to the overlay/ directory to serve as static files. Optional (omit for tests).
+ * @returns {Promise<{ setState: (update: object) => object, stop: () => Promise<void> }>}
+ */
+function startServer({ port, overlayDir }) {
+  let currentState = { ...initialState };
+
+  const app = express();
+  const server = http.createServer(app);
+  const wss = new WebSocketServer({ server });
+
+  // CORS: overlay/OBS browser sources may be loaded from arbitrary origins.
+  app.use((req, res, next) => {
+    res.header('Access-Control-Allow-Origin', '*');
+    res.header('Access-Control-Allow-Methods', 'GET, OPTIONS');
+    res.header('Access-Control-Allow-Headers', 'Content-Type');
+    if (req.method === 'OPTIONS') return res.sendStatus(204);
+    next();
+  });
+
+  app.get('/api/health', (req, res) => res.json({ status: 'ok' }));
+
+  app.get('/api/now-playing', (req, res) => res.json(currentState));
+
+  // Image proxy so overlay clients can fetch album art that may have CORS / referrer restrictions.
+  app.get('/api/image-proxy', async (req, res) => {
+    const url = req.query.url;
+    if (!url) return res.status(400).send('Missing url parameter');
+    try {
+      const response = await fetch(url);
+      if (!response.ok) return res.status(response.status).send('Upstream error');
+      res.set('Content-Type', response.headers.get('content-type') || 'image/jpeg');
+      res.set('Cache-Control', 'public, max-age=3600');
+      const buffer = await response.arrayBuffer();
+      res.send(Buffer.from(buffer));
+    } catch (err) {
+      res.status(502).send('Failed to fetch image');
+    }
+  });
+
+  if (overlayDir) {
+    app.use(express.static(overlayDir));
+  }
+
+  wss.on('connection', (ws) => {
+    ws.send(JSON.stringify(currentState));
+  });
+
+  function setState(update) {
+    currentState = mergeState(currentState, update || {});
+    const message = JSON.stringify(currentState);
+    wss.clients.forEach((client) => {
+      if (client.readyState === 1) client.send(message);
+    });
+    return currentState;
+  }
+
+  function stop() {
+    return new Promise((resolve) => {
+      wss.close(() => server.close(() => resolve()));
+    });
+  }
+
+  return new Promise((resolve, reject) => {
+    server.listen(port, '127.0.0.1', () => {
+      console.log(`[wtm] server listening on http://127.0.0.1:${port}`);
+      resolve({ setState, stop });
+    });
+    server.on('error', reject);
+  });
+}
+
+module.exports = { startServer };