from __future__ import annotations import copy import inspect import logging import warnings import weakref from collections.abc import Generator, Mapping, Sequence from contextlib import contextmanager from contextvars import ContextVar, Token from dataclasses import dataclass from enum import Enum from logging import Logger from typing import Any, Literal, cast, get_origin, overload import anyio from mcp import LoggingLevel, ServerSession from mcp.server.lowlevel.helper_types import ReadResourceContents from mcp.server.lowlevel.server import request_ctx from mcp.shared.context import RequestContext from mcp.types import ( AudioContent, ClientCapabilities, CreateMessageResult, GetPromptResult, ImageContent, IncludeContext, ModelHint, ModelPreferences, Root, SamplingCapability, SamplingMessage, TextContent, ) from mcp.types import CreateMessageRequestParams as SamplingParams from mcp.types import Prompt as MCPPrompt from mcp.types import Resource as MCPResource from pydantic.networks import AnyUrl from starlette.requests import Request from typing_extensions import TypeVar import fastmcp.server.dependencies from fastmcp import settings from fastmcp.server.elicitation import ( AcceptedElicitation, CancelledElicitation, DeclinedElicitation, ScalarElicitationType, get_elicitation_schema, ) from fastmcp.server.server import FastMCP from fastmcp.utilities.logging import _clamp_logger, get_logger from fastmcp.utilities.types import get_cached_typeadapter logger: Logger = get_logger(name=__name__) to_client_logger: Logger = logger.getChild(suffix="to_client") # Convert all levels of server -> client messages to debug level # This clamp can be undone at runtime by calling `_unclamp_logger` or calling # `_clamp_logger` with a different max level. _clamp_logger(logger=to_client_logger, max_level="DEBUG") T = TypeVar("T", default=Any) _current_context: ContextVar[Context | None] = ContextVar("context", default=None) # type: ignore[assignment] _flush_lock = anyio.Lock() @dataclass class LogData: """Data object for passing log arguments to client-side handlers. This provides an interface to match the Python standard library logging, for compatibility with structured logging. """ msg: str extra: Mapping[str, Any] | None = None _mcp_level_to_python_level = { "debug": logging.DEBUG, "info": logging.INFO, "notice": logging.INFO, "warning": logging.WARNING, "error": logging.ERROR, "critical": logging.CRITICAL, "alert": logging.CRITICAL, "emergency": logging.CRITICAL, } @contextmanager def set_context(context: Context) -> Generator[Context, None, None]: token = _current_context.set(context) try: yield context finally: _current_context.reset(token) @dataclass class Context: """Context object providing access to MCP capabilities. This provides a cleaner interface to MCP's RequestContext functionality. It gets injected into tool and resource functions that request it via type hints. To use context in a tool function, add a parameter with the Context type annotation: ```python @server.tool async def my_tool(x: int, ctx: Context) -> str: # Log messages to the client await ctx.info(f"Processing {x}") await ctx.debug("Debug info") await ctx.warning("Warning message") await ctx.error("Error message") # Report progress await ctx.report_progress(50, 100, "Processing") # Access resources data = await ctx.read_resource("resource://data") # Get request info request_id = ctx.request_id client_id = ctx.client_id # Manage state across the request ctx.set_state("key", "value") value = ctx.get_state("key") return str(x) ``` State Management: Context objects maintain a state dictionary that can be used to store and share data across middleware and tool calls within a request. When a new context is created (nested contexts), it inherits a copy of its parent's state, ensuring that modifications in child contexts don't affect parent contexts. The context parameter name can be anything as long as it's annotated with Context. The context is optional - tools that don't need it can omit the parameter. """ def __init__(self, fastmcp: FastMCP): self._fastmcp: weakref.ref[FastMCP] = weakref.ref(fastmcp) self._tokens: list[Token] = [] self._notification_queue: set[str] = set() # Dedupe notifications self._state: dict[str, Any] = {} @property def fastmcp(self) -> FastMCP: """Get the FastMCP instance.""" fastmcp = self._fastmcp() if fastmcp is None: raise RuntimeError("FastMCP instance is no longer available") return fastmcp async def __aenter__(self) -> Context: """Enter the context manager and set this context as the current context.""" parent_context = _current_context.get(None) if parent_context is not None: # Inherit state from parent context self._state = copy.deepcopy(parent_context._state) # Always set this context and save the token token = _current_context.set(self) self._tokens.append(token) return self async def __aexit__(self, exc_type, exc_val, exc_tb) -> None: """Exit the context manager and reset the most recent token.""" # Flush any remaining notifications before exiting await self._flush_notifications() if self._tokens: token = self._tokens.pop() _current_context.reset(token) @property def request_context(self) -> RequestContext[ServerSession, Any, Request] | None: """Access to the underlying request context. Returns None when the MCP session has not been established yet. Returns the full RequestContext once the MCP session is available. For HTTP request access in middleware, use `get_http_request()` from fastmcp.server.dependencies, which works whether or not the MCP session is available. Example in middleware: ```python async def on_request(self, context, call_next): ctx = context.fastmcp_context if ctx.request_context: # MCP session available - can access session_id, request_id, etc. session_id = ctx.session_id else: # MCP session not available yet - use HTTP helpers from fastmcp.server.dependencies import get_http_request request = get_http_request() return await call_next(context) ``` """ try: return request_ctx.get() except LookupError: return None async def report_progress( 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 """ progress_token = ( self.request_context.meta.progressToken if self.request_context and self.request_context.meta else None ) if progress_token is None: return await self.session.send_progress_notification( progress_token=progress_token, progress=progress, total=total, message=message, related_request_id=self.request_id, ) async def list_resources(self) -> list[MCPResource]: """List all available resources from the server. Returns: List of Resource objects available on the server """ return await self.fastmcp._list_resources_mcp() async def list_prompts(self) -> list[MCPPrompt]: """List all available prompts from the server. Returns: List of Prompt objects available on the server """ return await self.fastmcp._list_prompts_mcp() async def get_prompt( self, name: str, arguments: dict[str, Any] | None = None ) -> GetPromptResult: """Get a prompt by name with optional arguments. Args: name: The name of the prompt to get arguments: Optional arguments to pass to the prompt Returns: The prompt result """ return await self.fastmcp._get_prompt_mcp(name, arguments) async def read_resource(self, uri: str | AnyUrl) -> list[ReadResourceContents]: """Read a resource by URI. Args: uri: Resource URI to read Returns: The resource content as either text or bytes """ return await self.fastmcp._read_resource_mcp(uri) async def log( self, message: str, level: LoggingLevel | None = None, logger_name: str | None = None, extra: Mapping[str, Any] | None = None, ) -> None: """Send a log message to the client. Messages sent to Clients are also logged to the `fastmcp.server.context.to_client` logger with a level of `DEBUG`. Args: message: Log message level: Optional log level. One of "debug", "info", "notice", "warning", "error", "critical", "alert", or "emergency". Default is "info". logger_name: Optional logger name extra: Optional mapping for additional arguments """ data = LogData(msg=message, extra=extra) await _log_to_server_and_client( data=data, session=self.session, level=level or "info", logger_name=logger_name, related_request_id=self.request_id, ) @property def client_id(self) -> str | None: """Get the client ID if available.""" return ( getattr(self.request_context.meta, "client_id", None) if self.request_context and self.request_context.meta else None ) @property def request_id(self) -> str: """Get the unique ID for this request. Raises RuntimeError if MCP request context is not available. """ if self.request_context is None: raise RuntimeError( "request_id is not available because the MCP session has not been established yet. " "Check `context.request_context` for None before accessing this attribute." ) return str(self.request_context.request_id) @property def session_id(self) -> str: """Get the MCP session ID for ALL transports. Returns the session ID that can be used as a key for session-based data storage (e.g., Redis) to share data between tool calls within the same client session. Returns: The session ID for StreamableHTTP transports, or a generated ID for other transports. Raises: RuntimeError if MCP request context is not available. Example: ```python @server.tool def store_data(data: dict, ctx: Context) -> str: session_id = ctx.session_id redis_client.set(f"session:{session_id}:data", json.dumps(data)) return f"Data stored for session {session_id}" ``` """ request_ctx = self.request_context if request_ctx is None: raise RuntimeError( "session_id is not available because the MCP session has not been established yet. " "Check `context.request_context` for None before accessing this attribute." ) session = request_ctx.session # Try to get the session ID from the session attributes session_id = getattr(session, "_fastmcp_id", None) if session_id is not None: return session_id # Try to get the session ID from the http request headers request = request_ctx.request if request: session_id = request.headers.get("mcp-session-id") # Generate a session ID if it doesn't exist. if session_id is None: from uuid import uuid4 session_id = str(uuid4()) # Save the session id to the session attributes session._fastmcp_id = session_id return session_id @property def session(self) -> ServerSession: """Access to the underlying session for advanced usage. Raises RuntimeError if MCP request context is not available. """ if self.request_context is None: raise RuntimeError( "session is not available because the MCP session has not been established yet. " "Check `context.request_context` for None before accessing this attribute." ) return self.request_context.session # Convenience methods for common log levels async def debug( self, message: str, logger_name: str | None = None, extra: Mapping[str, Any] | None = None, ) -> None: """Send a `DEBUG`-level message to the connected MCP Client. Messages sent to Clients are also logged to the `fastmcp.server.context.to_client` logger with a level of `DEBUG`.""" await self.log( level="debug", message=message, logger_name=logger_name, extra=extra, ) async def info( self, message: str, logger_name: str | None = None, extra: Mapping[str, Any] | None = None, ) -> None: """Send a `INFO`-level message to the connected MCP Client. Messages sent to Clients are also logged to the `fastmcp.server.context.to_client` logger with a level of `DEBUG`.""" await self.log( level="info", message=message, logger_name=logger_name, extra=extra, ) async def warning( self, message: str, logger_name: str | None = None, extra: Mapping[str, Any] | None = None, ) -> None: """Send a `WARNING`-level message to the connected MCP Client. Messages sent to Clients are also logged to the `fastmcp.server.context.to_client` logger with a level of `DEBUG`.""" await self.log( level="warning", message=message, logger_name=logger_name, extra=extra, ) async def error( self, message: str, logger_name: str | None = None, extra: Mapping[str, Any] | None = None, ) -> None: """Send a `ERROR`-level message to the connected MCP Client. Messages sent to Clients are also logged to the `fastmcp.server.context.to_client` logger with a level of `DEBUG`.""" await self.log( level="error", message=message, logger_name=logger_name, extra=extra, ) async def list_roots(self) -> list[Root]: """List the roots available to the server, as indicated by the client.""" result = await self.session.list_roots() return result.roots async def send_tool_list_changed(self) -> None: """Send a tool list changed notification to the client.""" await self.session.send_tool_list_changed() async def send_resource_list_changed(self) -> None: """Send a resource list changed notification to the client.""" await self.session.send_resource_list_changed() async def send_prompt_list_changed(self) -> None: """Send a prompt list changed notification to the client.""" await self.session.send_prompt_list_changed() async def sample( self, messages: str | Sequence[str | SamplingMessage], system_prompt: str | None = None, include_context: IncludeContext | None = None, temperature: float | None = None, max_tokens: int | None = None, model_preferences: ModelPreferences | str | list[str] | None = None, ) -> TextContent | ImageContent | AudioContent: """ Send a sampling request to the client and await the response. Call this method at any time to have the server request an LLM completion from the client. The client must be appropriately configured, or the request will error. """ if max_tokens is None: max_tokens = 512 if isinstance(messages, str): sampling_messages = [ SamplingMessage( content=TextContent(text=messages, type="text"), role="user" ) ] elif isinstance(messages, Sequence): sampling_messages = [ SamplingMessage(content=TextContent(text=m, type="text"), role="user") if isinstance(m, str) else m for m in messages ] should_fallback = ( self.fastmcp.sampling_handler_behavior == "fallback" and not self.session.check_client_capability( capability=ClientCapabilities(sampling=SamplingCapability()) ) ) if self.fastmcp.sampling_handler_behavior == "always" or should_fallback: if self.fastmcp.sampling_handler is None: raise ValueError("Client does not support sampling") create_message_result = self.fastmcp.sampling_handler( sampling_messages, SamplingParams( systemPrompt=system_prompt, messages=sampling_messages, temperature=temperature, maxTokens=max_tokens, modelPreferences=_parse_model_preferences(model_preferences), ), self.request_context, ) if inspect.isawaitable(create_message_result): create_message_result = await create_message_result if isinstance(create_message_result, str): return TextContent(text=create_message_result, type="text") if isinstance(create_message_result, CreateMessageResult): return create_message_result.content else: raise ValueError( f"Unexpected sampling handler result: {create_message_result}" ) result: CreateMessageResult = await self.session.create_message( messages=sampling_messages, system_prompt=system_prompt, include_context=include_context, temperature=temperature, max_tokens=max_tokens, model_preferences=_parse_model_preferences(model_preferences), related_request_id=self.request_id, ) return result.content @overload async def elicit( self, message: str, response_type: None, ) -> ( AcceptedElicitation[dict[str, Any]] | DeclinedElicitation | CancelledElicitation ): ... """When response_type is None, the accepted elicitation will contain an empty dict""" @overload async def elicit( self, message: str, response_type: type[T], ) -> AcceptedElicitation[T] | DeclinedElicitation | CancelledElicitation: ... """When response_type is not None, the accepted elicitation will contain the response data""" @overload async def elicit( self, message: str, response_type: list[str], ) -> AcceptedElicitation[str] | DeclinedElicitation | CancelledElicitation: ... """When response_type is a list of strings, the accepted elicitation will contain the selected string response""" async def elicit( self, message: str, response_type: type[T] | list[str] | None = None, ) -> ( AcceptedElicitation[T] | AcceptedElicitation[dict[str, Any]] | AcceptedElicitation[str] | DeclinedElicitation | CancelledElicitation ): """ Send an elicitation request to the client and await the response. Call this method at any time to request additional information from the user through the client. The client must support elicitation, or the request will error. Note that the MCP protocol only supports simple object schemas with primitive types. You can provide a dataclass, TypedDict, or BaseModel to comply. If you provide a primitive type, an object schema with a single "value" field will be generated for the MCP interaction and automatically deconstructed into the primitive type upon response. If the response_type is None, the generated schema will be that of an empty object in order to comply with the MCP protocol requirements. Clients must send an empty object ("{}")in response. Args: message: A human-readable message explaining what information is needed response_type: The type of the response, which should be a primitive type or dataclass or BaseModel. If it is a primitive type, an object schema with a single "value" field will be generated. """ if response_type is None: schema = {"type": "object", "properties": {}} else: # if the user provided a list of strings, treat it as a Literal if isinstance(response_type, list): if not all(isinstance(item, str) for item in response_type): raise ValueError( "List of options must be a list of strings. Received: " f"{response_type}" ) # Convert list of options to Literal type and wrap choice_literal = Literal[tuple(response_type)] # type: ignore response_type = ScalarElicitationType[choice_literal] # type: ignore # if the user provided a primitive scalar, wrap it in an object schema elif ( response_type in {bool, int, float, str} or get_origin(response_type) is Literal or (isinstance(response_type, type) and issubclass(response_type, Enum)) ): response_type = ScalarElicitationType[response_type] # type: ignore response_type = cast(type[T], response_type) schema = get_elicitation_schema(response_type) result = await self.session.elicit( message=message, requestedSchema=schema, related_request_id=self.request_id, ) if result.action == "accept": if response_type is not None: type_adapter = get_cached_typeadapter(response_type) validated_data = cast( T | ScalarElicitationType[T], type_adapter.validate_python(result.content), ) if isinstance(validated_data, ScalarElicitationType): return AcceptedElicitation[T](data=validated_data.value) else: return AcceptedElicitation[T](data=cast(T, validated_data)) elif result.content: raise ValueError( "Elicitation expected an empty response, but received: " f"{result.content}" ) else: return AcceptedElicitation[dict[str, Any]](data={}) elif result.action == "decline": return DeclinedElicitation() elif result.action == "cancel": return CancelledElicitation() else: # This should never happen, but handle it just in case raise ValueError(f"Unexpected elicitation action: {result.action}") def get_http_request(self) -> Request: """Get the active starlette request.""" # Deprecated in 2.2.11 if settings.deprecation_warnings: warnings.warn( "Context.get_http_request() is deprecated and will be removed in a future version. " "Use get_http_request() from fastmcp.server.dependencies instead. " "See https://gofastmcp.com/servers/context#http-requests for more details.", DeprecationWarning, stacklevel=2, ) return fastmcp.server.dependencies.get_http_request() def set_state(self, key: str, value: Any) -> None: """Set a value in the context state.""" self._state[key] = value def get_state(self, key: str) -> Any: """Get a value from the context state. Returns None if the key is not found.""" return self._state.get(key) def _queue_tool_list_changed(self) -> None: """Queue a tool list changed notification.""" self._notification_queue.add("notifications/tools/list_changed") def _queue_resource_list_changed(self) -> None: """Queue a resource list changed notification.""" self._notification_queue.add("notifications/resources/list_changed") def _queue_prompt_list_changed(self) -> None: """Queue a prompt list changed notification.""" self._notification_queue.add("notifications/prompts/list_changed") async def _flush_notifications(self) -> None: """Send all queued notifications.""" async with _flush_lock: if not self._notification_queue: return try: if "notifications/tools/list_changed" in self._notification_queue: await self.session.send_tool_list_changed() if "notifications/resources/list_changed" in self._notification_queue: await self.session.send_resource_list_changed() if "notifications/prompts/list_changed" in self._notification_queue: await self.session.send_prompt_list_changed() self._notification_queue.clear() except Exception: # Don't let notification failures break the request pass def _parse_model_preferences( model_preferences: ModelPreferences | str | list[str] | None, ) -> ModelPreferences | None: """ Validates and converts user input for model_preferences into a ModelPreferences object. Args: model_preferences (ModelPreferences | str | list[str] | None): The model preferences to use. Accepts: - ModelPreferences (returns as-is) - str (single model hint) - list[str] (multiple model hints) - None (no preferences) Returns: ModelPreferences | None: The parsed ModelPreferences object, or None if not provided. Raises: ValueError: If the input is not a supported type or contains invalid values. """ if model_preferences is None: return None elif isinstance(model_preferences, ModelPreferences): return model_preferences elif isinstance(model_preferences, str): # Single model hint return ModelPreferences(hints=[ModelHint(name=model_preferences)]) elif isinstance(model_preferences, list): # List of model hints (strings) if not all(isinstance(h, str) for h in model_preferences): raise ValueError( "All elements of model_preferences list must be" " strings (model name hints)." ) return ModelPreferences(hints=[ModelHint(name=h) for h in model_preferences]) else: raise ValueError( "model_preferences must be one of: ModelPreferences, str, list[str], or None." ) async def _log_to_server_and_client( data: LogData, session: ServerSession, level: LoggingLevel, logger_name: str | None = None, related_request_id: str | None = None, ) -> None: """Log a message to the server and client.""" msg_prefix = f"Sending {level.upper()} to client" if logger_name: msg_prefix += f" ({logger_name})" to_client_logger.log( level=_mcp_level_to_python_level[level], msg=f"{msg_prefix}: {data.msg}", extra=data.extra, ) await session.send_log_message( level=level, data=data, logger=logger_name, related_request_id=related_request_id, )