fix: improve port assignment for VPN instances

Modified the port assignment logic to avoid potential collisions by pre-filtering used ports before selecting from the available pool. This ensures each VPN instance gets a unique port more efficiently, reducing the risk of assignment conflicts and improving the reliability of VPN setup.

coldbrew/vpn/models.py

@@ -33,11 +33,13 @@ class VPN(models.Model):
 
         self.public_key = get_public_key(self.private_key)
 
-        while not self.port:
-            port = random.randint(10000, 40000)
+        if not self.port:
+            pool = list(range(10000, 40000))
 
-            if not VPN.objects.filter(port=port).exists():
-                self.port = port
+            for vpn in VPN.objects.all():
+                pool.remove(vpn.port)
+
+            self.port = random.choice(pool)
 
         super().save(*args, **kwargs)