Upgraded VPN blocker with self-clearing cache.

src/util/vpnDetection.ts

@@ -1,22 +1,65 @@
 import { RequestHandler } from 'express';
 
+const VPN_TIMEOUT = 1000 * 60 * 60 * 12; // 12 hours
+
 let whitelistedUsernames: string[] = [];
 if (process.env.WHITELISTED_VPN_USERNAMES) {
   whitelistedUsernames = process.env.WHITELISTED_VPN_USERNAMES.split(',');
 }
 
-const vpnCache: Map<string, boolean> = new Map();
+class VpnEntry {
+  // Default it to True in case it fails.
+  private isVpn = true;
+  private isSet = false;
+  private timeCreated: Date;
+
+  constructor(timeCreated: Date) {
+    this.timeCreated = timeCreated;
+  }
+
+  isTimedOut(newTime: Date): boolean {
+    // + on a date object implicitly casts it to a number
+    const timeDiffMillis = +newTime - +this.timeCreated;
+
+    return timeDiffMillis > VPN_TIMEOUT;
+  }
+
+  getIsVpn(): boolean {
+    return this.isVpn;
+  }
+
+  setIsVpn(isVpn: boolean): void {
+    if (this.isSet) {
+      throw new Error(
+        'VpnEntry has already been set. Should not never be set again.',
+      );
+    }
+
+    this.isVpn = isVpn;
+    this.isSet = true;
+  }
+}
+
+type IP = string;
+
+const vpnCache: Map<IP, VpnEntry> = new Map();
 
 const isVPN = async (ip: string): Promise<boolean> => {
   // Temporarily disable VPN checking
   return false;
 
   if (vpnCache.has(ip)) {
-    return vpnCache.get(ip);
+    // Clear the cache entry if it's timed out.
+    if (vpnCache.get(ip).isTimedOut(new Date())) {
+      vpnCache.delete(ip);
+    }
+    // Otherwise we have a valid entry. Directly return.
+    else {
+      return vpnCache.get(ip).getIsVpn();
+    }
   }
 
-  // Default it to True in case it fails.
-  vpnCache.set(ip, true);
+  vpnCache.set(ip, new VpnEntry(new Date()));
   console.log(`Checking VPN status of ip: ${ip}`);
   console.log(`VPN Cache size: ${vpnCache.size}`);
 
@@ -35,7 +78,7 @@ const isVPN = async (ip: string): Promise<boolean> => {
 
   const result: boolean = data.security.vpn;
 
-  vpnCache.set(ip, result);
+  vpnCache.get(ip).setIsVpn(result);
 
   return result;
 };