use mta field for related_request_id

Author: ihrpr

src/mcp/server/streamableHttp.py

@@ -600,10 +600,13 @@ async def message_router():
                         if isinstance(
                             message.root, JSONRPCNotification | JSONRPCRequest
                         ):
-                            # Extract related_request_id from params if it exists
-                            if (params := getattr(message.root, "params", None)) and (
-                                related_id := params.get("related_request_id")
-                            ) is not None:
+                            # Extract related_request_id from meta if it exists
+                            if (
+                                (params := getattr(message.root, "params", None))
+                                and (meta := params.get("_meta"))
+                                and (related_id := meta.get("related_request_id"))
+                                is not None
+                            ):
                                 target_request_id = str(related_id)
                         else:
                             target_request_id = str(message.root.id)

src/mcp/shared/session.py

@@ -6,7 +6,6 @@
 from typing import Any, Generic, TypeVar
 
 import anyio
-import anyio.lowlevel
 import httpx
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import BaseModel
@@ -24,6 +23,7 @@
     JSONRPCNotification,
     JSONRPCRequest,
     JSONRPCResponse,
+    NotificationParams,
     RequestParams,
     ServerNotification,
     ServerRequest,
@@ -276,8 +276,23 @@ async def send_notification(
         Emits a notification, which is a one-way message that does not expect
         a response.
         """
+        # Some transport implementations may need to set the related_request_id
+        # to attribute to the notifications to the request that triggered
+        # them.
+        # Update notification meta with related request ID if provided
         if related_request_id is not None and notification.root.params is not None:
-            notification.root.params.related_request_id = related_request_id
+            # Create meta if it doesn't exist
+            if notification.root.params.meta is None:
+                # Create meta dict with related_request_id
+                meta_dict = {"related_request_id": related_request_id}
+
+            else:
+                # Update existing meta with model_validate to properly handle extra fields
+                meta_dict = notification.root.params.meta.model_dump(
+                    by_alias=True, mode="json", exclude_none=True
+                )
+                meta_dict["related_request_id"] = related_request_id
+            notification.root.params.meta = NotificationParams.Meta(**meta_dict)
         jsonrpc_notification = JSONRPCNotification(
             jsonrpc="2.0",
             **notification.model_dump(by_alias=True, mode="json", exclude_none=True),

src/mcp/types.py

@@ -58,7 +58,6 @@ class Meta(BaseModel):
         model_config = ConfigDict(extra="allow")
 
     meta: Meta | None = Field(alias="_meta", default=None)
-    related_request_id: RequestId | None = None
     """
     This parameter name is reserved by MCP to allow clients and servers to attach
     additional metadata to their notifications.

tests/client/test_logging_callback.py

@@ -9,6 +9,7 @@
 from mcp.shared.session import RequestResponder
 from mcp.types import (
     LoggingMessageNotificationParams,
+    NotificationParams,
     TextContent,
 )
 
@@ -78,6 +79,11 @@ async def message_handler(
         )
         assert log_result.isError is False
         assert len(logging_collector.log_messages) == 1
-        assert logging_collector.log_messages[0] == LoggingMessageNotificationParams(
-            level="info", logger="test_logger", data="Test log message"
-        )
+        # Create meta object with related_request_id added dynamically
+        meta = NotificationParams.Meta()
+        setattr(meta, "related_request_id", "2")
+        log = logging_collector.log_messages[0]
+        assert log.level == "info"
+        assert log.logger == "test_logger"
+        assert log.data == "Test log message"
+        assert log.meta == meta

tests/server/fastmcp/test_server.py

@@ -544,14 +544,28 @@ async def logging_tool(msg: str, ctx: Context) -> str:
 
                 assert mock_log.call_count == 4
                 mock_log.assert_any_call(
-                    level="debug", data="Debug message", logger=None
+                    level="debug",
+                    data="Debug message",
+                    logger=None,
+                    related_request_id="1",
                 )
-                mock_log.assert_any_call(level="info", data="Info message", logger=None)
                 mock_log.assert_any_call(
-                    level="warning", data="Warning message", logger=None
+                    level="info",
+                    data="Info message",
+                    logger=None,
+                    related_request_id="1",
                 )
                 mock_log.assert_any_call(
-                    level="error", data="Error message", logger=None
+                    level="warning",
+                    data="Warning message",
+                    logger=None,
+                    related_request_id="1",
+                )
+                mock_log.assert_any_call(
+                    level="error",
+                    data="Error message",
+                    logger=None,
+                    related_request_id="1",
                 )
 
     @pytest.mark.anyio