Fix JSON-RPC notification format in Streamable HTTP transport

Update send_notification method to properly construct JSON-RPC notification objects with jsonrpc version and method fields.
This ensures notifications conform to the JSON-RPC 2.0 specification when sent over HTTP transport.

https://www.jsonrpc.org/specification#notification

Another goal is to standardise the `send_notification` interface.
Before the revision, it was sufficient to pass the method and parameters in the case of stdio.
However, in the case of Streamable, a hash based on the JSON-RPC specification must be passed.

Author: dak2

lib/mcp/server/transports/streamable_http_transport.rb

@@ -34,7 +34,13 @@ def close
           end
         end
 
-        def send_notification(notification, session_id: nil)
+        def send_notification(method, params = nil, session_id: nil)
+          notification = {
+            jsonrpc: "2.0",
+            method:,
+          }
+          notification[:params] = params if params
+
           @mutex.synchronize do
             if session_id
               # Send to specific session

test/mcp/server/transports/streamable_http_notification_integration_test.rb

@@ -58,9 +58,9 @@ class StreamableHTTPNotificationIntegrationTest < ActiveSupport::TestCase
           io.rewind
           output = io.read
 
-          assert_includes output, "data: #{Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED}"
-          assert_includes output, "data: #{Methods::NOTIFICATIONS_PROMPTS_LIST_CHANGED}"
-          assert_includes output, "data: #{Methods::NOTIFICATIONS_RESOURCES_LIST_CHANGED}"
+          assert_includes output, "data: {\"jsonrpc\":\"2.0\",\"method\":\"#{Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED}\"}"
+          assert_includes output, "data: {\"jsonrpc\":\"2.0\",\"method\":\"#{Methods::NOTIFICATIONS_PROMPTS_LIST_CHANGED}\"}"
+          assert_includes output, "data: {\"jsonrpc\":\"2.0\",\"method\":\"#{Methods::NOTIFICATIONS_RESOURCES_LIST_CHANGED}\"}"
         end
 
         test "notifications are broadcast to all connected sessions" do
@@ -111,11 +111,11 @@ class StreamableHTTPNotificationIntegrationTest < ActiveSupport::TestCase
           # Check both sessions received the notification
           io1.rewind
           output1 = io1.read
-          assert_includes output1, "data: #{Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED}"
+          assert_includes output1, "data: {\"jsonrpc\":\"2.0\",\"method\":\"#{Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED}\"}"
 
           io2.rewind
           output2 = io2.read
-          assert_includes output2, "data: #{Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED}"
+          assert_includes output2, "data: {\"jsonrpc\":\"2.0\",\"method\":\"#{Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED}\"}"
         end
 
         test "server continues to work when SSE connection is closed" do
@@ -191,7 +191,7 @@ class StreamableHTTPNotificationIntegrationTest < ActiveSupport::TestCase
           # Check the notification was received
           io.rewind
           output = io.read
-          assert_includes output, "data: #{Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED}"
+          assert_includes output, "data: {\"jsonrpc\":\"2.0\",\"method\":\"#{Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED}\"}"
 
           # Verify the tool was added to the server
           assert @server.tools.key?("dynamic_tool")
@@ -229,7 +229,7 @@ class StreamableHTTPNotificationIntegrationTest < ActiveSupport::TestCase
           output = io.read
 
           # SSE format should be "data: <message>\n\n"
-          assert_match(/data: #{Regexp.escape(Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED)}\n/, output)
+          assert_match(/data: \{"jsonrpc":"2\.0","method":"#{Regexp.escape(Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED)}"\}\n/, output)
         end
 
         private

test/mcp/server/transports/streamable_http_transport_test.rb

@@ -391,8 +391,7 @@ class StreamableHTTPTransportTest < ActiveSupport::TestCase
           @server.define_singleton_method(:handle_json) do |request|
             result = original_handle_json.call(request)
             # Send notification while still in request context - broadcast to all sessions
-            notification = { jsonrpc: "2.0", method: "test_notification", params: { session: "current" } }
-            transport.send_notification(notification)
+            transport.send_notification("test_notification", { session: "current" })
             result
           end
 
@@ -452,8 +451,7 @@ class StreamableHTTPTransportTest < ActiveSupport::TestCase
           sleep(0.1)
 
           # Send notification to specific session
-          notification = { jsonrpc: "2.0", method: "test_notification", params: { message: "Hello" } }
-          result = @transport.send_notification(notification, session_id: session_id)
+          result = @transport.send_notification("test_notification", { message: "Hello" }, session_id: session_id)
 
           assert result
 
@@ -507,8 +505,7 @@ class StreamableHTTPTransportTest < ActiveSupport::TestCase
           sleep(0.1)
 
           # Broadcast notification to all sessions
-          notification = { jsonrpc: "2.0", method: "broadcast", params: { message: "Hello everyone" } }
-          sent_count = @transport.send_notification(notification)
+          sent_count = @transport.send_notification("broadcast", { message: "Hello everyone" })
 
           assert_equal 2, sent_count