feat: add client IP diagnostics and blocking

back/shared/clientIp.ts

@@ -0,0 +1,29 @@
+import { Request } from 'express';
+
+const IPV4_MAPPED_PREFIX = '::ffff:';
+
+export function normalizeClientIp(value?: string): string {
+  let ip = (value || '').trim().toLowerCase();
+  if (!ip) {
+    return '';
+  }
+
+  if (ip.startsWith('[') && ip.endsWith(']')) {
+    ip = ip.slice(1, -1);
+  }
+
+  const zoneIndex = ip.indexOf('%');
+  if (zoneIndex !== -1) {
+    ip = ip.slice(0, zoneIndex);
+  }
+
+  if (ip.startsWith(IPV4_MAPPED_PREFIX)) {
+    return ip.slice(IPV4_MAPPED_PREFIX.length);
+  }
+
+  return ip;
+}
+
+export function getClientIp(req: Request): string {
+  return normalizeClientIp(req.ip || req.socket.remoteAddress);
+}