feat(api): add unified v2 gateway and mobile read slice

backend/unified-api/src/routes/proxy.js

@@ -0,0 +1,75 @@
+import { Router } from 'express';
+import { AppError } from '../lib/errors.js';
+
+const HOP_BY_HOP_HEADERS = new Set([
+  'connection',
+  'content-length',
+  'host',
+  'keep-alive',
+  'proxy-authenticate',
+  'proxy-authorization',
+  'te',
+  'trailer',
+  'transfer-encoding',
+  'upgrade',
+]);
+
+function resolveTargetBase(pathname) {
+  if (pathname.startsWith('/core')) return process.env.CORE_API_BASE_URL;
+  if (pathname.startsWith('/commands')) return process.env.COMMAND_API_BASE_URL;
+  if (pathname.startsWith('/query')) return process.env.QUERY_API_BASE_URL;
+  return null;
+}
+
+function copyHeaders(source, target) {
+  for (const [key, value] of source.entries()) {
+    if (HOP_BY_HOP_HEADERS.has(key.toLowerCase())) continue;
+    target.setHeader(key, value);
+  }
+}
+
+async function forwardRequest(req, res, next, fetchImpl) {
+  try {
+    const requestPath = new URL(req.originalUrl, 'http://localhost').pathname;
+    const baseUrl = resolveTargetBase(requestPath);
+    if (!baseUrl) {
+      throw new AppError('NOT_FOUND', `No upstream configured for ${requestPath}`, 404);
+    }
+
+    const url = new URL(req.originalUrl, baseUrl);
+    const headers = new Headers();
+    for (const [key, value] of Object.entries(req.headers)) {
+      if (value == null || HOP_BY_HOP_HEADERS.has(key.toLowerCase())) continue;
+      if (Array.isArray(value)) {
+        for (const item of value) headers.append(key, item);
+      } else {
+        headers.set(key, value);
+      }
+    }
+    headers.set('x-request-id', req.requestId);
+
+    const upstream = await fetchImpl(url, {
+      method: req.method,
+      headers,
+      body: req.method === 'GET' || req.method === 'HEAD' ? undefined : req,
+      duplex: req.method === 'GET' || req.method === 'HEAD' ? undefined : 'half',
+    });
+
+    copyHeaders(upstream.headers, res);
+    res.status(upstream.status);
+
+    const buffer = Buffer.from(await upstream.arrayBuffer());
+    return res.send(buffer);
+  } catch (error) {
+    return next(error);
+  }
+}
+
+export function createProxyRouter(options = {}) {
+  const router = Router();
+  const fetchImpl = options.fetchImpl || fetch;
+
+  router.use(['/core', '/commands', '/query'], (req, res, next) => forwardRequest(req, res, next, fetchImpl));
+
+  return router;
+}