content: """
  SSE Server Transport Module
  
  This module implements a Server-Sent Events (SSE) transport layer for MCP servers.
  
  Example usage:
  ```
      # Create an SSE transport at an endpoint
      sse = SseServerTransport("/messages/")
  
      # Create Starlette routes for SSE and message handling
      routes = [
          Route("/sse", endpoint=handle_sse, methods=["GET"]),
          Mount("/messages/", app=sse.handle_post_message),
      ]
  
      # Define handler functions
      async def handle_sse(request):
          async with sse.connect_sse(
              request.scope, request.receive, request._send
          ) as streams:
              await app.run(
                  streams[0], streams[1], app.create_initialization_options()
              )
          # Return empty response to avoid NoneType error
          return Response()
  
      # Create and run Starlette app
      starlette_app = Starlette(routes=routes)
      uvicorn.run(starlette_app, host="127.0.0.1", port=port)
  ```
  
  Note: The handle_sse function must return a Response to avoid a "TypeError: 'NoneType'
  object is not callable" error when client disconnects. The example above returns
  an empty Response() after the SSE connection ends to fix this.
  
  See SseServerTransport class documentation for more details.
  """
  
  import logging
  from contextlib import asynccontextmanager
  from typing import Any
  from urllib.parse import quote
  from uuid import UUID, uuid4
  
  import anyio
  from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
  from pydantic import ValidationError
  from sse_starlette import EventSourceResponse
  from starlette.requests import Request
  from starlette.responses import Response
  from starlette.types import Receive, Scope, Send
  
  import mcp.types as types
  from mcp.server.transport_security import (
      TransportSecurityMiddleware,
      TransportSecuritySettings,
  )
  from mcp.shared.message import ServerMessageMetadata, SessionMessage
  
  logger = logging.getLogger(__name__)
  
  
  class SseServerTransport:
      """
      SSE server transport for MCP. This class provides _two_ ASGI applications,
      suitable to be used with a framework like Starlette and a server like Hypercorn:
  
          1. connect_sse() is an ASGI application which receives incoming GET requests,
             and sets up a new SSE stream to send server messages to the client.
          2. handle_post_message() is an ASGI application which receives incoming POST
             requests, which should contain client messages that link to a
             previously-established SSE session.
      """
  
      _endpoint: str
      _read_stream_writers: dict[UUID, MemoryObjectSendStream[SessionMessage | Exception]]
      _security: TransportSecurityMiddleware
  
      def __init__(self, endpoint: str, security_settings: TransportSecuritySettings | None = None) -> None:
          """
          Creates a new SSE server transport, which will direct the client to POST
          messages to the relative path given.
  
          Args:
              endpoint: A relative path where messages should be posted
                      (e.g., "/messages/").
              security_settings: Optional security settings for DNS rebinding protection.
  
          Note:
              We use relative paths instead of full URLs for several reasons:
              1. Security: Prevents cross-origin requests by ensuring clients only connect
                 to the same origin they established the SSE connection with
              2. Flexibility: The server can be mounted at any path without needing to
                 know its full URL
              3. Portability: The same endpoint configuration works across different
                 environments (development, staging, production)
  
          Raises:
              ValueError: If the endpoint is a full URL instead of a relative path
          """
  
          super().__init__()
  
          # Validate that endpoint is a relative path and not a full URL
          if "://" in endpoint or endpoint.startswith("//") or "?" in endpoint or "#" in endpoint:
              raise ValueError(
                  f"Given endpoint: {endpoint} is not a relative path (e.g., '/messages/'), "
                  "expecting a relative path (e.g., '/messages/')."
              )
  
          # Ensure endpoint starts with a forward slash
          if not endpoint.startswith("/"):
              endpoint = "/" + endpoint
  
          self._endpoint = endpoint
          self._read_stream_writers = {}
          self._security = TransportSecurityMiddleware(security_settings)
          logger.debug(f"SseServerTransport initialized with endpoint: {endpoint}")
  
      @asynccontextmanager
      async def connect_sse(self, scope: Scope, receive: Receive, send: Send):  # pragma: no cover
          if scope["type"] != "http":
              logger.error("connect_sse received non-HTTP request")
              raise ValueError("connect_sse can only handle HTTP requests")
  
          # Validate request headers for DNS rebinding protection
          request = Request(scope, receive)
          error_response = await self._security.validate_request(request, is_post=False)
          if error_response:
              await error_response(scope, receive, send)
              raise ValueError("Request validation failed")
  
          logger.debug("Setting up SSE connection")
          read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
          read_stream_writer: MemoryObjectSendStream[SessionMessage | Exception]
  
          write_stream: MemoryObjectSendStream[SessionMessage]
          write_stream_reader: MemoryObjectReceiveStream[SessionMessage]
  
          read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
          write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
  
          session_id = uuid4()
          self._read_stream_writers[session_id] = read_stream_writer
          logger.debug(f"Created new session with ID: {session_id}")
  
          # Determine the full path for the message endpoint to be sent to the client.
          # scope['root_path'] is the prefix where the current Starlette app
          # instance is mounted.
          # e.g., "" if top-level, or "/api_prefix" if mounted under "/api_prefix".
          root_path = scope.get("root_path", "")
  
          # self._endpoint is the path *within* this app, e.g., "/messages".
          # Concatenating them gives the full absolute path from the server root.
          # e.g., "" + "/messages" -> "/messages"
          # e.g., "/api_prefix" + "/messages" -> "/api_prefix/messages"
          full_message_path_for_client = root_path.rstrip("/") + self._endpoint
  
          # This is the URI (path + query) the client will use to POST messages.
          client_post_uri_data = f"{quote(full_message_path_for_client)}?session_id={session_id.hex}"
  
          sse_stream_writer, sse_stream_reader = anyio.create_memory_object_stream[dict[str, Any]](0)
  
          async def sse_writer():
              logger.debug("Starting SSE writer")
              async with sse_stream_writer, write_stream_reader:
                  await sse_stream_writer.send({"event": "endpoint", "data": client_post_uri_data})
                  logger.debug(f"Sent endpoint event: {client_post_uri_data}")
  
                  async for session_message in write_stream_reader:
                      logger.debug(f"Sending message via SSE: {session_message}")
                      await sse_stream_writer.send(
                          {
                              "event": "message",
                              "data": session_message.message.model_dump_json(by_alias=True, exclude_none=True),
                          }
                      )
  
          async with anyio.create_task_group() as tg:
  
              async def response_wrapper(scope: Scope, receive: Receive, send: Send):
                  """
                  The EventSourceResponse returning signals a client close / disconnect.
                  In this case we close our side of the streams to signal the client that
                  the connection has been closed.
                  """
                  await EventSourceResponse(content=sse_stream_reader, data_sender_callable=sse_writer)(
                      scope, receive, send
                  )
                  await read_stream_writer.aclose()
                  await write_stream_reader.aclose()
                  logging.debug(f"Client session disconnected {session_id}")
  
              logger.debug("Starting SSE response task")
              tg.start_soon(response_wrapper, scope, receive, send)
  
              logger.debug("Yielding read and write streams")
              yield (read_stream, write_stream)
  
      async def handle_post_message(self, scope: Scope, receive: Receive, send: Send) -> None:  # pragma: no cover
          logger.debug("Handling POST message")
          request = Request(scope, receive)
  
          # Validate request headers for DNS rebinding protection
          error_response = await self._security.validate_request(request, is_post=True)
          if error_response:
              return await error_response(scope, receive, send)
  
          session_id_param = request.query_params.get("session_id")
          if session_id_param is None:
              logger.warning("Received request without session_id")
              response = Response("session_id is required", status_code=400)
              return await response(scope, receive, send)
  
          try:
              session_id = UUID(hex=session_id_param)
              logger.debug(f"Parsed session ID: {session_id}")
          except ValueError:
              logger.warning(f"Received invalid session ID: {session_id_param}")
              response = Response("Invalid session ID", status_code=400)
              return await response(scope, receive, send)
  
          writer = self._read_stream_writers.get(session_id)
          if not writer:
              logger.warning(f"Could not find session for ID: {session_id}")
              response = Response("Could not find session", status_code=404)
              return await response(scope, receive, send)
  
          body = await request.body()
          logger.debug(f"Received JSON: {body}")
  
          try:
              message = types.JSONRPCMessage.model_validate_json(body)
              logger.debug(f"Validated client message: {message}")
          except ValidationError as err:
              logger.exception("Failed to parse message")
              response = Response("Could not parse message", status_code=400)
              await response(scope, receive, send)
              await writer.send(err)
              return
  
          # Pass the ASGI scope for framework-agnostic access to request data
          metadata = ServerMessageMetadata(request_context=request)
          session_message = SessionMessage(message, metadata=metadata)
          logger.debug(f"Sending session message to writer: {session_message}")
          response = Response("Accepted", status_code=202)
          await response(scope, receive, send)
          await writer.send(session_message)
  