StreamableHttp - Server transport with state management

examples/servers/simple-streamablehttp/README.md

@@ -0,0 +1,37 @@
+# MCP Simple StreamableHttp Server Example
+
+A simple MCP server example demonstrating the StreamableHttp transport, which enables HTTP-based communication with MCP servers using streaming.
+
+## Features
+
+- Uses the StreamableHTTP transport for server-client communication
+- Supports REST API operations (POST, GET, DELETE) for `/mcp` endpoint
+- Task management with anyio task groups
+- Ability to send multiple notifications over time to the client
+- Proper resource cleanup and lifespan management
+
+## Usage
+
+Start the server on the default or custom port:
+
+```bash
+
+# Using custom port
+uv run mcp-simple-streamablehttp --port 3000
+
+# Custom logging level
+uv run mcp-simple-streamablehttp --log-level DEBUG
+
+# Enable JSON responses instead of SSE streams
+uv run mcp-simple-streamablehttp --json-response
+```
+
+The server exposes a tool named "start-notification-stream" that accepts three arguments:
+
+- `interval`: Time between notifications in seconds (e.g., 1.0)
+- `count`: Number of notifications to send (e.g., 5)
+- `caller`: Identifier string for the caller
+
+## Client
+
+You can connect to this server using an HTTP client, for now only Typescript SDK has streamable HTTP client examples or you can use (Inspector)[https://github.com/modelcontextprotocol/inspector]

examples/servers/simple-streamablehttp/mcp_simple_streamablehttp/__main__.py

@@ -0,0 +1,4 @@
+from .server import main
+
+if __name__ == "__main__":
+    main()

examples/servers/simple-streamablehttp/mcp_simple_streamablehttp/server.py

@@ -0,0 +1,201 @@
+import contextlib
+import logging
+from http import HTTPStatus
+from uuid import uuid4
+
+import anyio
+import click
+import mcp.types as types
+from mcp.server.lowlevel import Server
+from mcp.server.streamableHttp import (
+    MCP_SESSION_ID_HEADER,
+    StreamableHTTPServerTransport,
+)
+from starlette.applications import Starlette
+from starlette.requests import Request
+from starlette.responses import Response
+from starlette.routing import Mount
+
+# Configure logging
+logger = logging.getLogger(__name__)
+
+# Global task group that will be initialized in the lifespan
+task_group = None
+
+
+@contextlib.asynccontextmanager
+async def lifespan(app):
+    """Application lifespan context manager for managing task group."""
+    global task_group
+
+    async with anyio.create_task_group() as tg:
+        task_group = tg
+        logger.info("Application started, task group initialized!")
+        try:
+            yield
+        finally:
+            logger.info("Application shutting down, cleaning up resources...")
+            if task_group:
+                tg.cancel_scope.cancel()
+                task_group = None
+            logger.info("Resources cleaned up successfully.")
+
+
+@click.command()
+@click.option("--port", default=3000, help="Port to listen on for HTTP")
+@click.option(
+    "--log-level",
+    default="INFO",
+    help="Logging level (DEBUG, INFO, WARNING, ERROR, CRITICAL)",
+)
+@click.option(
+    "--json-response",
+    is_flag=True,
+    default=False,
+    help="Enable JSON responses instead of SSE streams",
+)
+def main(
+    port: int,
+    log_level: str,
+    json_response: bool,
+) -> int:
+    # Configure logging
+    logging.basicConfig(
+        level=getattr(logging, log_level.upper()),
+        format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
+    )
+
+    app = Server("mcp-streamable-http-demo")
+
+    @app.call_tool()
+    async def call_tool(
+        name: str, arguments: dict
+    ) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
+        ctx = app.request_context
+        interval = arguments.get("interval", 1.0)
+        count = arguments.get("count", 5)
+        caller = arguments.get("caller", "unknown")
+
+        # Send the specified number of notifications with the given interval
+        for i in range(count):
+            await ctx.session.send_log_message(
+                level="info",
+                data=f"Notification {i+1}/{count} from caller: {caller}",
+                logger="notification_stream",
+                # Associates this notification with the original request
+                # Ensures notifications are sent to the correct response stream
+                # Without this, notifications will either go to:
+                # - a standalone SSE stream (if GET request is supported)
+                # - nowhere (if GET request isn't supported)
+                related_request_id=ctx.request_id,
+            )
+            if i < count - 1:  # Don't wait after the last notification
+                await anyio.sleep(interval)
+
+        return [
+            types.TextContent(
+                type="text",
+                text=(
+                    f"Sent {count} notifications with {interval}s interval"
+                    f" for caller: {caller}"
+                ),
+            )
+        ]
+
+    @app.list_tools()
+    async def list_tools() -> list[types.Tool]:
+        return [
+            types.Tool(
+                name="start-notification-stream",
+                description=(
+                    "Sends a stream of notifications with configurable count"
+                    " and interval"
+                ),
+                inputSchema={
+                    "type": "object",
+                    "required": ["interval", "count", "caller"],
+                    "properties": {
+                        "interval": {
+                            "type": "number",
+                            "description": "Interval between notifications in seconds",
+                        },
+                        "count": {
+                            "type": "number",
+                            "description": "Number of notifications to send",
+                        },
+                        "caller": {
+                            "type": "string",
+                            "description": (
+                                "Identifier of the caller to include in notifications"
+                            ),
+                        },
+                    },
+                },
+            )
+        ]
+
+    # We need to store the server instances between requests
+    server_instances = {}
+    # Lock to prevent race conditions when creating new sessions
+    session_creation_lock = anyio.Lock()
+
+    # ASGI handler for streamable HTTP connections
+    async def handle_streamable_http(scope, receive, send):
+        request = Request(scope, receive)
+        request_mcp_session_id = request.headers.get(MCP_SESSION_ID_HEADER)
+        if (
+            request_mcp_session_id is not None
+            and request_mcp_session_id in server_instances
+        ):
+            transport = server_instances[request_mcp_session_id]
+            logger.debug("Session already exists, handling request directly")
+            await transport.handle_request(scope, receive, send)
+        elif request_mcp_session_id is None:
+            # try to establish new session
+            logger.debug("Creating new transport")
+            # Use lock to prevent race conditions when creating new sessions
+            async with session_creation_lock:
+                new_session_id = uuid4().hex
+                http_transport = StreamableHTTPServerTransport(
+                    mcp_session_id=new_session_id,
+                    is_json_response_enabled=json_response,
+                )
+                server_instances[http_transport.mcp_session_id] = http_transport
+            async with http_transport.connect() as streams:
+                read_stream, write_stream = streams
+
+                async def run_server():
+                    await app.run(
+                        read_stream,
+                        write_stream,
+                        app.create_initialization_options(),
+                    )
+
+                if not task_group:
+                    raise RuntimeError("Task group is not initialized")
+
+                task_group.start_soon(run_server)
+
+                # Handle the HTTP request and return the response
+                await http_transport.handle_request(scope, receive, send)
+        else:
+            response = Response(
+                "Bad Request: No valid session ID provided",
+                status_code=HTTPStatus.BAD_REQUEST,
+            )
+            await response(scope, receive, send)
+
+    # Create an ASGI application using the transport
+    starlette_app = Starlette(
+        debug=True,
+        routes=[
+            Mount("/mcp", app=handle_streamable_http),
+        ],
+        lifespan=lifespan,
+    )
+
+    import uvicorn
+
+    uvicorn.run(starlette_app, host="0.0.0.0", port=port)
+
+    return 0

examples/servers/simple-streamablehttp/pyproject.toml

@@ -0,0 +1,36 @@
+[project]
+name = "mcp-simple-streamablehttp"
+version = "0.1.0"
+description = "A simple MCP server exposing a StreamableHttp transport for testing"
+readme = "README.md"
+requires-python = ">=3.10"
+authors = [{ name = "Anthropic, PBC." }]
+keywords = ["mcp", "llm", "automation", "web", "fetch", "http", "streamable"]
+license = { text = "MIT" }
+dependencies = ["anyio>=4.5", "click>=8.1.0", "httpx>=0.27", "mcp", "starlette", "uvicorn"]
+
+[project.scripts]
+mcp-simple-streamablehttp = "mcp_simple_streamablehttp.server:main"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["mcp_simple_streamablehttp"]
+
+[tool.pyright]
+include = ["mcp_simple_streamablehttp"]
+venvPath = "."
+venv = ".venv"
+
+[tool.ruff.lint]
+select = ["E", "F", "I"]
+ignore = []
+
+[tool.ruff]
+line-length = 88
+target-version = "py310"
+
+[tool.uv]
+dev-dependencies = ["pyright>=1.1.378", "pytest>=8.3.3", "ruff>=0.6.9"]

src/mcp/server/fastmcp/server.py

@@ -674,7 +674,10 @@ async def log(
             **extra: Additional structured data to include
         """
         await self.request_context.session.send_log_message(
-            level=level, data=message, logger=logger_name
+            level=level,
+            data=message,
+            logger=logger_name,
+            related_request_id=self.request_id,
         )
 
     @property

src/mcp/server/session.py

@@ -179,7 +179,11 @@ async def _received_notification(
                     )
 
     async def send_log_message(
-        self, level: types.LoggingLevel, data: Any, logger: str | None = None
+        self,
+        level: types.LoggingLevel,
+        data: Any,
+        logger: str | None = None,
+        related_request_id: types.RequestId | None = None,
     ) -> None:
         """Send a log message notification."""
         await self.send_notification(
@@ -192,7 +196,8 @@ async def send_log_message(
                         logger=logger,
                     ),
                 )
-            )
+            ),
+            related_request_id,
         )
 
     async def send_resource_updated(self, uri: AnyUrl) -> None:
@@ -261,7 +266,11 @@ async def send_ping(self) -> types.EmptyResult:
         )
 
     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,
+        related_request_id: str | None = None,
     ) -> None:
         """Send a progress notification."""
         await self.send_notification(
@@ -274,7 +283,8 @@ async def send_progress_notification(
                         total=total,
                     ),
                 )
-            )
+            ),
+            related_request_id,
         )
 
     async def send_resource_list_changed(self) -> None: