Fix IPAddr prefix information missing when write to cache in msgpack …

…serializer

* Save cache size by omit the prefix if unnecessary

* rename to straightforward naming.

* check the prefix directly instead of inspect

* Remove unused helper method

* add to changelog

Co-authored-by: Jonathan Hefner <jonathan@hefner.pro>

activesupport/CHANGELOG.md

@@ -1,3 +1,10 @@
+*   Include `IPAddr#prefix` when serializing an `IPAddr` using the
+    `ActiveSupport::MessagePack` serializer. This change is backward and forward
+    compatible — old payloads can still be read, and new payloads will be
+    readable by older versions of Rails.
+
+    *Taiki Komaba*
+
 *   Add `default:` support for `ActiveSupport::CurrentAttributes.attribute`
 
     ```ruby

activesupport/lib/active_support/message_pack/extensions.rb

@@ -86,8 +86,9 @@ def install(registry)
           unpacker: URI.method(:parse)
 
         registry.register_type 14, IPAddr,
-          packer: :to_s,
-          unpacker: :new
+          packer: method(:write_ipaddr),
+          unpacker: method(:read_ipaddr),
+          recursive: true
 
         registry.register_type 15, Pathname,
           packer: :to_s,
@@ -221,6 +222,18 @@ def read_set(unpacker)
         Set.new(unpacker.read)
       end
 
+      def write_ipaddr(ipaddr, packer)
+        if ipaddr.prefix < 32 || (ipaddr.ipv6? && ipaddr.prefix < 128)
+          packer.write("#{ipaddr}/#{ipaddr.prefix}")
+        else
+          packer.write(ipaddr.to_s)
+        end
+      end
+
+      def read_ipaddr(unpacker)
+        IPAddr.new(unpacker.read)
+      end
+
       def write_hash_with_indifferent_access(hwia, packer)
         packer.write(hwia.to_h)
       end

activesupport/test/message_pack/shared_serializer_tests.rb

@@ -127,6 +127,12 @@ module MessagePackSharedSerializerTests
 
     test "roundtrips IPAddr" do
       assert_roundtrip IPAddr.new("127.0.0.1")
+      assert_roundtrip IPAddr.new("1.1.1.1/16")
+      assert_equal 16, load(dump(IPAddr.new("1.1.1.1/16"))).prefix
+
+      assert_roundtrip IPAddr.new("::1")
+      assert_roundtrip IPAddr.new("1:1:1:1:1:1:1:1/64")
+      assert_equal 64, load(dump(IPAddr.new("1:1:1:1:1:1:1:1/64"))).prefix
     end
 
     test "roundtrips Pathname" do