Fix #4736: Display network prefix length (if present) in API key IP whitelist.

app/logical/danbooru/ip_address.rb

@@ -0,0 +1,23 @@
+# A wrapper around the IPAddress gem that adds some extra utility methods.
+#
+# https://github.com/ipaddress-gem/ipaddress
+
+module Danbooru
+  class IpAddress
+    attr_reader :ip_address
+    delegate_missing_to :ip_address
+
+    def initialize(string)
+      @ip_address = ::IPAddress.parse(string)
+    end
+
+    # "1.2.3.4/24" if the address is a subnet, "1.2.3.4" otherwise.
+    def to_s
+      ip_address.size > 1 ? ip_address.to_string : ip_address.to_s
+    end
+
+    def inspect
+      "#<Danbooru::IpAddress #{to_s}>"
+    end
+  end
+end

app/logical/ip_address_type.rb

@@ -1,9 +1,14 @@
+# See also config/initializers/types.rb
+
+require "active_record/connection_adapters/postgresql_adapter"
+
 class IpAddressType < ActiveRecord::ConnectionAdapters::PostgreSQL::OID::Inet
   def cast(value)
-    super(IPAddress.parse(value))
+    return nil if value.blank?
+    super(Danbooru::IpAddress.new(value))
   end
 
   def serialize(value)
-    value.to_string
+    value&.to_string
   end
 end