mcp-python-sdk/src/mcp/server/fastmcp/server.py

"""FastMCP - A more ergonomic interface for MCP servers."""

from __future__ import annotations as _annotations

import inspect
import json
import re
from collections.abc import AsyncIterator, Callable, Iterable, Sequence
from contextlib import (
    AbstractAsyncContextManager,
    asynccontextmanager,
)
from itertools import chain
from typing import Any, Generic, Literal

import anyio
import pydantic_core
import uvicorn
from pydantic import BaseModel, Field
from pydantic.networks import AnyUrl
from pydantic_settings import BaseSettings, SettingsConfigDict
from starlette.applications import Starlette
from starlette.requests import Request
from starlette.routing import Mount, Route

from mcp.server.fastmcp.exceptions import ResourceError
from mcp.server.fastmcp.prompts import Prompt, PromptManager
from mcp.server.fastmcp.resources import FunctionResource, Resource, ResourceManager
from mcp.server.fastmcp.tools import ToolManager
from mcp.server.fastmcp.utilities.logging import configure_logging, get_logger
from mcp.server.fastmcp.utilities.types import Image
from mcp.server.lowlevel.helper_types import ReadResourceContents
from mcp.server.lowlevel.server import LifespanResultT
from mcp.server.lowlevel.server import Server as MCPServer
from mcp.server.lowlevel.server import lifespan as default_lifespan
from mcp.server.session import ServerSession, ServerSessionT
from mcp.server.sse import SseServerTransport
from mcp.server.stdio import stdio_server
from mcp.shared.context import LifespanContextT, RequestContext
from mcp.types import (
    AnyFunction,
    EmbeddedResource,
    GetPromptResult,
    ImageContent,
    TextContent,
)
from mcp.types import Prompt as MCPPrompt
from mcp.types import PromptArgument as MCPPromptArgument
from mcp.types import Resource as MCPResource
from mcp.types import ResourceTemplate as MCPResourceTemplate
from mcp.types import Tool as MCPTool

logger = get_logger(__name__)


class Settings(BaseSettings, Generic[LifespanResultT]):
    """FastMCP server settings.

    All settings can be configured via environment variables with the prefix FASTMCP_.
    For example, FASTMCP_DEBUG=true will set debug=True.
    """

    model_config = SettingsConfigDict(
        env_prefix="FASTMCP_",
        env_file=".env",
        extra="ignore",
    )

    # Server settings
    debug: bool = False
    log_level: Literal["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"] = "INFO"

    # HTTP settings
    host: str = "0.0.0.0"
    port: int = 8000
    sse_path: str = "/sse"
    message_path: str = "/messages/"

    # resource settings
    warn_on_duplicate_resources: bool = True

    # tool settings
    warn_on_duplicate_tools: bool = True

    # prompt settings
    warn_on_duplicate_prompts: bool = True

    dependencies: list[str] = Field(
        default_factory=list,
        description="List of dependencies to install in the server environment",
    )

    lifespan: (
        Callable[[FastMCP], AbstractAsyncContextManager[LifespanResultT]] | None
    ) = Field(None, description="Lifespan context manager")


def lifespan_wrapper(
    app: FastMCP,
    lifespan: Callable[[FastMCP], AbstractAsyncContextManager[LifespanResultT]],
) -> Callable[[MCPServer[LifespanResultT]], AbstractAsyncContextManager[object]]:
    @asynccontextmanager
    async def wrap(s: MCPServer[LifespanResultT]) -> AsyncIterator[object]:
        async with lifespan(app) as context:
            yield context

    return wrap


class FastMCP:
    def __init__(
        self, name: str | None = None, instructions: str | None = None, **settings: Any
    ):
        self.settings = Settings(**settings)

        self._mcp_server = MCPServer(
            name=name or "FastMCP",
            instructions=instructions,
            lifespan=lifespan_wrapper(self, self.settings.lifespan)
            if self.settings.lifespan
            else default_lifespan,
        )
        self._tool_manager = ToolManager(
            warn_on_duplicate_tools=self.settings.warn_on_duplicate_tools
        )
        self._resource_manager = ResourceManager(
            warn_on_duplicate_resources=self.settings.warn_on_duplicate_resources
        )
        self._prompt_manager = PromptManager(
            warn_on_duplicate_prompts=self.settings.warn_on_duplicate_prompts
        )
        self.dependencies = self.settings.dependencies

        # Set up MCP protocol handlers
        self._setup_handlers()

        # Configure logging
        configure_logging(self.settings.log_level)

    @property
    def name(self) -> str:
        return self._mcp_server.name

    @property
    def instructions(self) -> str | None:
        return self._mcp_server.instructions

    def run(self, transport: Literal["stdio", "sse"] = "stdio") -> None:
        """Run the FastMCP server. Note this is a synchronous function.

        Args:
            transport: Transport protocol to use ("stdio" or "sse")
        """
        TRANSPORTS = Literal["stdio", "sse"]
        if transport not in TRANSPORTS.__args__:  # type: ignore
            raise ValueError(f"Unknown transport: {transport}")

        if transport == "stdio":
            anyio.run(self.run_stdio_async)
        else:  # transport == "sse"
            anyio.run(self.run_sse_async)

    def _setup_handlers(self) -> None:
        """Set up core MCP protocol handlers."""
        self._mcp_server.list_tools()(self.list_tools)
        self._mcp_server.call_tool()(self.call_tool)
        self._mcp_server.list_resources()(self.list_resources)
        self._mcp_server.read_resource()(self.read_resource)
        self._mcp_server.list_prompts()(self.list_prompts)
        self._mcp_server.get_prompt()(self.get_prompt)
        self._mcp_server.list_resource_templates()(self.list_resource_templates)

    async def list_tools(self) -> list[MCPTool]:
        """List all available tools."""
        tools = self._tool_manager.list_tools()
        return [
            MCPTool(
                name=info.name,
                description=info.description,
                inputSchema=info.parameters,
            )
            for info in tools
        ]

    def get_context(self) -> Context[ServerSession, object]:
        """
        Returns a Context object. Note that the context will only be valid
        during a request; outside a request, most methods will error.
        """
        try:
            request_context = self._mcp_server.request_context
        except LookupError:
            request_context = None
        return Context(request_context=request_context, fastmcp=self)

    async def call_tool(
        self, name: str, arguments: dict[str, Any]
    ) -> Sequence[TextContent | ImageContent | EmbeddedResource]:
        """Call a tool by name with arguments."""
        context = self.get_context()
        result = await self._tool_manager.call_tool(name, arguments, context=context)
        converted_result = _convert_to_content(result)
        return converted_result

    async def list_resources(self) -> list[MCPResource]:
        """List all available resources."""

        resources = self._resource_manager.list_resources()
        return [
            MCPResource(
                uri=resource.uri,
                name=resource.name or "",
                description=resource.description,
                mimeType=resource.mime_type,
            )
            for resource in resources
        ]

    async def list_resource_templates(self) -> list[MCPResourceTemplate]:
        templates = self._resource_manager.list_templates()
        return [
            MCPResourceTemplate(
                uriTemplate=template.uri_template,
                name=template.name,
                description=template.description,
            )
            for template in templates
        ]

    async def read_resource(self, uri: AnyUrl | str) -> Iterable[ReadResourceContents]:
        """Read a resource by URI."""

        resource = await self._resource_manager.get_resource(uri)
        if not resource:
            raise ResourceError(f"Unknown resource: {uri}")

        try:
            content = await resource.read()
            return [ReadResourceContents(content=content, mime_type=resource.mime_type)]
        except Exception as e:
            logger.error(f"Error reading resource {uri}: {e}")
            raise ResourceError(str(e))

    def add_tool(
        self,
        fn: AnyFunction,
        name: str | None = None,
        description: str | None = None,
    ) -> None:
        """Add a tool to the server.

        The tool function can optionally request a Context object by adding a parameter
        with the Context type annotation. See the @tool decorator for examples.

        Args:
            fn: The function to register as a tool
            name: Optional name for the tool (defaults to function name)
            description: Optional description of what the tool does
        """
        self._tool_manager.add_tool(fn, name=name, description=description)

    def tool(
        self, name: str | None = None, description: str | None = None
    ) -> Callable[[AnyFunction], AnyFunction]:
        """Decorator to register a tool.

        Tools can optionally request a Context object by adding a parameter with the
        Context type annotation. The context provides access to MCP capabilities like
        logging, progress reporting, and resource access.

        Args:
            name: Optional name for the tool (defaults to function name)
            description: Optional description of what the tool does

        Example:
            @server.tool()
            def my_tool(x: int) -> str:
                return str(x)

            @server.tool()
            def tool_with_context(x: int, ctx: Context) -> str:
                ctx.info(f"Processing {x}")
                return str(x)

            @server.tool()
            async def async_tool(x: int, context: Context) -> str:
                await context.report_progress(50, 100)
                return str(x)
        """
        # Check if user passed function directly instead of calling decorator
        if callable(name):
            raise TypeError(
                "The @tool decorator was used incorrectly. "
                "Did you forget to call it? Use @tool() instead of @tool"
            )

        def decorator(fn: AnyFunction) -> AnyFunction:
            self.add_tool(fn, name=name, description=description)
            return fn

        return decorator

    def add_resource(self, resource: Resource) -> None:
        """Add a resource to the server.

        Args:
            resource: A Resource instance to add
        """
        self._resource_manager.add_resource(resource)

    def resource(
        self,
        uri: str,
        *,
        name: str | None = None,
        description: str | None = None,
        mime_type: str | None = None,
    ) -> Callable[[AnyFunction], AnyFunction]:
        """Decorator to register a function as a resource.

        The function will be called when the resource is read to generate its content.
        The function can return:
        - str for text content
        - bytes for binary content
        - other types will be converted to JSON

        If the URI contains parameters (e.g. "resource://{param}") or the function
        has parameters, it will be registered as a template resource.

        Args:
            uri: URI for the resource (e.g. "resource://my-resource" or "resource://{param}")
            name: Optional name for the resource
            description: Optional description of the resource
            mime_type: Optional MIME type for the resource

        Example:
            @server.resource("resource://my-resource")
            def get_data() -> str:
                return "Hello, world!"

            @server.resource("resource://my-resource")
            async get_data() -> str:
                data = await fetch_data()
                return f"Hello, world! {data}"

            @server.resource("resource://{city}/weather")
            def get_weather(city: str) -> str:
                return f"Weather for {city}"

            @server.resource("resource://{city}/weather")
            async def get_weather(city: str) -> str:
                data = await fetch_weather(city)
                return f"Weather for {city}: {data}"
        """
        # Check if user passed function directly instead of calling decorator
        if callable(uri):
            raise TypeError(
                "The @resource decorator was used incorrectly. "
                "Did you forget to call it? Use @resource('uri') instead of @resource"
            )

        def decorator(fn: AnyFunction) -> AnyFunction:
            # Check if this should be a template
            has_uri_params = "{" in uri and "}" in uri
            has_func_params = bool(inspect.signature(fn).parameters)

            if has_uri_params or has_func_params:
                # Validate that URI params match function params
                uri_params = set(re.findall(r"{(\w+)}", uri))
                func_params = set(inspect.signature(fn).parameters.keys())

                if uri_params != func_params:
                    raise ValueError(
                        f"Mismatch between URI parameters {uri_params} "
                        f"and function parameters {func_params}"
                    )

                # Register as template
                self._resource_manager.add_template(
                    fn=fn,
                    uri_template=uri,
                    name=name,
                    description=description,
                    mime_type=mime_type or "text/plain",
                )
            else:
                # Register as regular resource
                resource = FunctionResource(
                    uri=AnyUrl(uri),
                    name=name,
                    description=description,
                    mime_type=mime_type or "text/plain",
                    fn=fn,
                )
                self.add_resource(resource)
            return fn

        return decorator

    def add_prompt(self, prompt: Prompt) -> None:
        """Add a prompt to the server.

        Args:
            prompt: A Prompt instance to add
        """
        self._prompt_manager.add_prompt(prompt)

    def prompt(
        self, name: str | None = None, description: str | None = None
    ) -> Callable[[AnyFunction], AnyFunction]:
        """Decorator to register a prompt.

        Args:
            name: Optional name for the prompt (defaults to function name)
            description: Optional description of what the prompt does

        Example:
            @server.prompt()
            def analyze_table(table_name: str) -> list[Message]:
                schema = read_table_schema(table_name)
                return [
                    {
                        "role": "user",
                        "content": f"Analyze this schema:\n{schema}"
                    }
                ]

            @server.prompt()
            async def analyze_file(path: str) -> list[Message]:
                content = await read_file(path)
                return [
                    {
                        "role": "user",
                        "content": {
                            "type": "resource",
                            "resource": {
                                "uri": f"file://{path}",
                                "text": content
                            }
                        }
                    }
                ]
        """
        # Check if user passed function directly instead of calling decorator
        if callable(name):
            raise TypeError(
                "The @prompt decorator was used incorrectly. "
                "Did you forget to call it? Use @prompt() instead of @prompt"
            )

        def decorator(func: AnyFunction) -> AnyFunction:
            prompt = Prompt.from_function(func, name=name, description=description)
            self.add_prompt(prompt)
            return func

        return decorator

    async def run_stdio_async(self) -> None:
        """Run the server using stdio transport."""
        async with stdio_server() as (read_stream, write_stream):
            await self._mcp_server.run(
                read_stream,
                write_stream,
                self._mcp_server.create_initialization_options(),
            )

    async def run_sse_async(self) -> None:
        """Run the server using SSE transport."""
        starlette_app = self.sse_app()

        config = uvicorn.Config(
            starlette_app,
            host=self.settings.host,
            port=self.settings.port,
            log_level=self.settings.log_level.lower(),
        )
        server = uvicorn.Server(config)
        await server.serve()

    def sse_app(self) -> Starlette:
        """Return an instance of the SSE server app."""
        sse = SseServerTransport(self.settings.message_path)

        async def handle_sse(request: Request) -> None:
            async with sse.connect_sse(
                request.scope,
                request.receive,
                request._send,  # type: ignore[reportPrivateUsage]
            ) as streams:
                await self._mcp_server.run(
                    streams[0],
                    streams[1],
                    self._mcp_server.create_initialization_options(),
                )

        return Starlette(
            debug=self.settings.debug,
            routes=[
                Route(self.settings.sse_path, endpoint=handle_sse),
                Mount(self.settings.message_path, app=sse.handle_post_message),
            ],
        )

    async def list_prompts(self) -> list[MCPPrompt]:
        """List all available prompts."""
        prompts = self._prompt_manager.list_prompts()
        return [
            MCPPrompt(
                name=prompt.name,
                description=prompt.description,
                arguments=[
                    MCPPromptArgument(
                        name=arg.name,
                        description=arg.description,
                        required=arg.required,
                    )
                    for arg in (prompt.arguments or [])
                ],
            )
            for prompt in prompts
        ]

    async def get_prompt(
        self, name: str, arguments: dict[str, Any] | None = None
    ) -> GetPromptResult:
        """Get a prompt by name with arguments."""
        try:
            messages = await self._prompt_manager.render_prompt(name, arguments)

            return GetPromptResult(messages=pydantic_core.to_jsonable_python(messages))
        except Exception as e:
            logger.error(f"Error getting prompt {name}: {e}")
            raise ValueError(str(e))


def _convert_to_content(
    result: Any,
) -> Sequence[TextContent | ImageContent | EmbeddedResource]:
    """Convert a result to a sequence of content objects."""
    if result is None:
        return []

    if isinstance(result, TextContent | ImageContent | EmbeddedResource):
        return [result]

    if isinstance(result, Image):
        return [result.to_image_content()]

    if isinstance(result, list | tuple):
        return list(chain.from_iterable(_convert_to_content(item) for item in result))  # type: ignore[reportUnknownVariableType]

    if not isinstance(result, str):
        try:
            result = json.dumps(pydantic_core.to_jsonable_python(result))
        except Exception:
            result = str(result)

    return [TextContent(type="text", text=result)]


class Context(BaseModel, Generic[ServerSessionT, LifespanContextT]):
    """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()
    def my_tool(x: int, ctx: Context) -> str:
        # Log messages to the client
        ctx.info(f"Processing {x}")
        ctx.debug("Debug info")
        ctx.warning("Warning message")
        ctx.error("Error message")

        # Report progress
        ctx.report_progress(50, 100)

        # Access resources
        data = ctx.read_resource("resource://data")

        # Get request info
        request_id = ctx.request_id
        client_id = ctx.client_id

        return str(x)
    ```

    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.
    """

    _request_context: RequestContext[ServerSessionT, LifespanContextT] | None
    _fastmcp: FastMCP | None

    def __init__(
        self,
        *,
        request_context: RequestContext[ServerSessionT, LifespanContextT] | None = None,
        fastmcp: FastMCP | None = None,
        **kwargs: Any,
    ):
        super().__init__(**kwargs)
        self._request_context = request_context
        self._fastmcp = fastmcp

    @property
    def fastmcp(self) -> FastMCP:
        """Access to the FastMCP server."""
        if self._fastmcp is None:
            raise ValueError("Context is not available outside of a request")
        return self._fastmcp

    @property
    def request_context(self) -> RequestContext[ServerSessionT, LifespanContextT]:
        """Access to the underlying request context."""
        if self._request_context is None:
            raise ValueError("Context is not available outside of a request")
        return self._request_context

    async def report_progress(
        self, progress: float, total: float | 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.meta
            else None
        )

        if progress_token is None:
            return

        await self.request_context.session.send_progress_notification(
            progress_token=progress_token, progress=progress, total=total
        )

    async def read_resource(self, uri: str | AnyUrl) -> Iterable[ReadResourceContents]:
        """Read a resource by URI.

        Args:
            uri: Resource URI to read

        Returns:
            The resource content as either text or bytes
        """
        assert (
            self._fastmcp is not None
        ), "Context is not available outside of a request"
        return await self._fastmcp.read_resource(uri)

    async def log(
        self,
        level: Literal["debug", "info", "warning", "error"],
        message: str,
        *,
        logger_name: str | None = None,
    ) -> None:
        """Send a log message to the client.

        Args:
            level: Log level (debug, info, warning, error)
            message: Log message
            logger_name: Optional logger name
            **extra: Additional structured data to include
        """
        await self.request_context.session.send_log_message(
            level=level, data=message, logger=logger_name
        )

    @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.meta
            else None
        )

    @property
    def request_id(self) -> str:
        """Get the unique ID for this request."""
        return str(self.request_context.request_id)

    @property
    def session(self):
        """Access to the underlying session for advanced usage."""
        return self.request_context.session

    # Convenience methods for common log levels
    async def debug(self, message: str, **extra: Any) -> None:
        """Send a debug log message."""
        await self.log("debug", message, **extra)

    async def info(self, message: str, **extra: Any) -> None:
        """Send an info log message."""
        await self.log("info", message, **extra)

    async def warning(self, message: str, **extra: Any) -> None:
        """Send a warning log message."""
        await self.log("warning", message, **extra)

    async def error(self, message: str, **extra: Any) -> None:
        """Send an error log message."""
        await self.log("error", message, **extra)