feat: add message to ProgressNotification (#435)

Co-authored-by: ihrpr <inna.hrpr@gmail.com>

src/mcp/client/session.py

@@ -168,7 +168,11 @@ class ClientSession(
         )
 
     async def send_progress_notification(
-        self, progress_token: str | int, progress: float, total: float | None = None
+        self,
+        progress_token: str | int,
+        progress: float,
+        total: float | None = None,
+        message: str | None = None,
     ) -> None:
         """Send a progress notification."""
         await self.send_notification(
@@ -179,6 +183,7 @@ class ClientSession(
                         progressToken=progress_token,
                         progress=progress,
                         total=total,
+                        message=message,
                     ),
                 ),
             )

src/mcp/server/fastmcp/server.py

@@ -952,13 +952,14 @@ class Context(BaseModel, Generic[ServerSessionT, LifespanContextT]):
         return self._request_context
 
     async def report_progress(
-        self, progress: float, total: float | None = None
+        self, progress: float, total: float | None = None, message: str | None = None
     ) -> None:
         """Report progress for the current operation.
 
         Args:
             progress: Current progress value e.g. 24
             total: Optional total value e.g. 100
+            message: Optional message e.g. Starting render...
         """
 
         progress_token = (
@@ -971,7 +972,10 @@ class Context(BaseModel, Generic[ServerSessionT, LifespanContextT]):
             return
 
         await self.request_context.session.send_progress_notification(
-            progress_token=progress_token, progress=progress, total=total
+            progress_token=progress_token,
+            progress=progress,
+            total=total,
+            message=message,
         )
 
     async def read_resource(self, uri: str | AnyUrl) -> Iterable[ReadResourceContents]:

src/mcp/server/lowlevel/server.py

@@ -37,7 +37,8 @@ Usage:
 3. Define notification handlers if needed:
    @server.progress_notification()
    async def handle_progress(
-       progress_token: str | int, progress: float, total: float | None
+       progress_token: str | int, progress: float, total: float | None,
+       message: str | None
    ) -> None:
        # Implementation
 
@@ -427,13 +428,18 @@ class Server(Generic[LifespanResultT]):
 
     def progress_notification(self):
         def decorator(
-            func: Callable[[str | int, float, float | None], Awaitable[None]],
+            func: Callable[
+                [str | int, float, float | None, str | None], Awaitable[None]
+            ],
         ):
             logger.debug("Registering handler for ProgressNotification")
 
             async def handler(req: types.ProgressNotification):
                 await func(
-                    req.params.progressToken, req.params.progress, req.params.total
+                    req.params.progressToken,
+                    req.params.progress,
+                    req.params.total,
+                    req.params.message,
                 )
 
             self.notification_handlers[types.ProgressNotification] = handler

src/mcp/server/session.py

@@ -282,6 +282,7 @@ class ServerSession(
         progress_token: str | int,
         progress: float,
         total: float | None = None,
+        message: str | None = None,
         related_request_id: str | None = None,
     ) -> None:
         """Send a progress notification."""
@@ -293,6 +294,7 @@ class ServerSession(
                         progressToken=progress_token,
                         progress=progress,
                         total=total,
+                        message=message,
                     ),
                 )
             ),

src/mcp/shared/progress.py

@@ -43,11 +43,11 @@ class ProgressContext(
     total: float | None
     current: float = field(default=0.0, init=False)
 
-    async def progress(self, amount: float) -> None:
+    async def progress(self, amount: float, message: str | None = None) -> None:
         self.current += amount
 
         await self.session.send_progress_notification(
-            self.progress_token, self.current, total=self.total
+            self.progress_token, self.current, total=self.total, message=message
         )
 
 

src/mcp/shared/session.py

@@ -401,7 +401,11 @@ class BaseSession(
         """
 
     async def send_progress_notification(
-        self, progress_token: str | int, progress: float, total: float | None = None
+        self,
+        progress_token: str | int,
+        progress: float,
+        total: float | None = None,
+        message: str | None = None,
     ) -> None:
         """
         Sends a progress notification for a request that is currently being

src/mcp/types.py

@@ -337,6 +337,11 @@ class ProgressNotificationParams(NotificationParams):
     total is unknown.
     """
     total: float | None = None
+    """
+    Message related to progress. This should provide relevant human readable 
+    progress information.
+    """
+    message: str | None = None
     """Total number of items to process (or total progress required), if known."""
     model_config = ConfigDict(extra="allow")