serializer: Add std::optional support

serializer.hh

@@ -27,6 +27,7 @@
 #include <seastar/core/sstring.hh>
 #include <unordered_map>
 #include <experimental/optional>
+#include <optional>
 #include "enum_set.hh"
 #include "utils/managed_bytes.hh"
 #include "bytes_ostream.hh"

serializer_impl.hh

@@ -540,6 +540,33 @@ void serialize_fragmented(Output& out, FragmentedBuffer&& v) {
     serializer<bytes>::write_fragmented(out, std::forward<FragmentedBuffer>(v));
 }
 
+template<typename T>
+struct serializer<std::optional<T>> {
+    template<typename Input>
+    static std::optional<T> read(Input& in) {
+        std::optional<T> v;
+        auto b = deserialize(in, boost::type<bool>());
+        if (b) {
+            v = deserialize(in, boost::type<T>());
+        }
+        return v;
+    }
+    template<typename Output>
+    static void write(Output& out, const std::optional<T>& v) {
+        serialize(out, bool(v));
+        if (v) {
+            serialize(out, v.value());
+        }
+    }
+    template<typename Input>
+    static void skip(Input& in) {
+        auto present = deserialize(in, boost::type<bool>());
+        if (present) {
+            serializer<T>::skip(in);
+        }
+    }
+};
+
 template<typename T>
 struct serializer<std::experimental::optional<T>> {
     template<typename Input>