From 7c1aa6ea497d3c330fb106e9dbd70797cbf72664 Mon Sep 17 00:00:00 2001
From: Jens Kraemer <jk@jkraemer.net>
Date: Mon, 21 Jul 2025 09:44:47 +0200
Subject: [PATCH 1/2] implements the notifications/initialized method

- According to
  https://modelcontextprotocol.io/specification/2025-06-18/basic/lifecycle,
  "After successful initialization, the client MUST send an initialized
  notification to indicate it is ready to begin normal operations".
- This implementation just replies with an empty response (same as ping).
---
 lib/mcp/server.rb       |  1 +
 test/mcp/server_test.rb | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/lib/mcp/server.rb b/lib/mcp/server.rb
index 2753589..8eed40a 100644
--- a/lib/mcp/server.rb
+++ b/lib/mcp/server.rb
@@ -66,6 +66,7 @@ def initialize(
         Methods::PROMPTS_GET => method(:get_prompt),
         Methods::INITIALIZE => method(:init),
         Methods::PING => ->(_) { {} },
+        Methods::NOTIFICATIONS_INITIALIZED => ->(_) { {} },
 
         # No op handlers for currently unsupported methods
         Methods::RESOURCES_SUBSCRIBE => ->(_) {},
diff --git a/test/mcp/server_test.rb b/test/mcp/server_test.rb
index 3e5853f..d564d4b 100644
--- a/test/mcp/server_test.rb
+++ b/test/mcp/server_test.rb
@@ -141,6 +141,25 @@ class ServerTest < ActiveSupport::TestCase
       assert_instrumentation_data({ method: "unsupported_method" })
     end
 
+    test "#handle notifications/initialized returns empty response" do
+      request = {
+        jsonrpc: "2.0",
+        method: "notifications/initialized",
+        id: "123",
+      }
+
+      response = @server.handle(request)
+      assert_equal(
+        {
+          jsonrpc: "2.0",
+          id: "123",
+          result: {},
+        },
+        response,
+      )
+      assert_instrumentation_data({ method: "notifications/initialized" })
+    end
+
     test "#handle tools/list returns available tools" do
       request = {
         jsonrpc: "2.0",

From c6063209d87a3e270fecf026f62b61005dce750c Mon Sep 17 00:00:00 2001
From: Jens Kraemer <jk@jkraemer.net>
Date: Tue, 22 Jul 2025 09:11:31 +0200
Subject: [PATCH 2/2] do not respond to notifications/initialized

- as per https://www.jsonrpc.org/specification#notification
---
 lib/mcp/server.rb       |  2 +-
 test/mcp/server_test.rb | 23 ++++++++++++-----------
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/lib/mcp/server.rb b/lib/mcp/server.rb
index 8eed40a..7cb0367 100644
--- a/lib/mcp/server.rb
+++ b/lib/mcp/server.rb
@@ -66,7 +66,7 @@ def initialize(
         Methods::PROMPTS_GET => method(:get_prompt),
         Methods::INITIALIZE => method(:init),
         Methods::PING => ->(_) { {} },
-        Methods::NOTIFICATIONS_INITIALIZED => ->(_) { {} },
+        Methods::NOTIFICATIONS_INITIALIZED => ->(_) {},
 
         # No op handlers for currently unsupported methods
         Methods::RESOURCES_SUBSCRIBE => ->(_) {},
diff --git a/test/mcp/server_test.rb b/test/mcp/server_test.rb
index d564d4b..ee0792b 100644
--- a/test/mcp/server_test.rb
+++ b/test/mcp/server_test.rb
@@ -141,22 +141,23 @@ class ServerTest < ActiveSupport::TestCase
       assert_instrumentation_data({ method: "unsupported_method" })
     end
 
-    test "#handle notifications/initialized returns empty response" do
+    test "#handle notifications/initialized returns nil response" do
       request = {
         jsonrpc: "2.0",
         method: "notifications/initialized",
-        id: "123",
       }
 
-      response = @server.handle(request)
-      assert_equal(
-        {
-          jsonrpc: "2.0",
-          id: "123",
-          result: {},
-        },
-        response,
-      )
+      assert_nil @server.handle(request)
+      assert_instrumentation_data({ method: "notifications/initialized" })
+    end
+
+    test "#handle_json notifications/initialized returns nil response" do
+      request = JSON.generate({
+        jsonrpc: "2.0",
+        method: "notifications/initialized",
+      })
+
+      assert_nil @server.handle_json(request)
       assert_instrumentation_data({ method: "notifications/initialized" })
     end