Method handler and handler result

src/main/java/dev/selimaj/session/types/HandlerResult.java

@@ -0,0 +1,6 @@
+package dev.selimaj.session.types;
+
+import com.fasterxml.jackson.databind.JsonNode;
+
+public record HandlerResult(boolean isError, JsonNode value) {
+}

src/main/java/dev/selimaj/session/types/MethodHandler.java

@@ -0,0 +1,10 @@
+package dev.selimaj.session.types;
+
+import com.fasterxml.jackson.databind.JsonNode;
+
+import java.util.concurrent.CompletableFuture;
+
+@FunctionalInterface
+public interface MethodHandler {
+    CompletableFuture<HandlerResult> handle(int id, JsonNode data);
+}