Integrate FastMCP

This commit integrates FastMCP, a high-level MCP server implementation originally written by Jeremiah Lowin,
into the official MCP SDK. It also updates dependencies and adds new dev dependencies.
It moves the existing SDK into a .lowlevel .

src/mcp/server/fastmcp/prompts/__init__.py

@@ -0,0 +1,4 @@
+from .base import Prompt
+from .manager import PromptManager
+
+__all__ = ["Prompt", "PromptManager"]

src/mcp/server/fastmcp/prompts/base.py

@@ -0,0 +1,166 @@
+"""Base classes for FastMCP prompts."""
+
+import json
+from typing import Any, Literal, Sequence, Awaitable
+import inspect
+from collections.abc import Callable
+
+from pydantic import BaseModel, Field, TypeAdapter, validate_call
+from mcp.types import TextContent, ImageContent, EmbeddedResource
+import pydantic_core
+
+CONTENT_TYPES = TextContent | ImageContent | EmbeddedResource
+
+
+class Message(BaseModel):
+    """Base class for all prompt messages."""
+
+    role: Literal["user", "assistant"]
+    content: CONTENT_TYPES
+
+    def __init__(self, content: str | CONTENT_TYPES, **kwargs):
+        if isinstance(content, str):
+            content = TextContent(type="text", text=content)
+        super().__init__(content=content, **kwargs)
+
+
+class UserMessage(Message):
+    """A message from the user."""
+
+    role: Literal["user", "assistant"] = "user"
+
+    def __init__(self, content: str | CONTENT_TYPES, **kwargs):
+        super().__init__(content=content, **kwargs)
+
+
+class AssistantMessage(Message):
+    """A message from the assistant."""
+
+    role: Literal["user", "assistant"] = "assistant"
+
+    def __init__(self, content: str | CONTENT_TYPES, **kwargs):
+        super().__init__(content=content, **kwargs)
+
+
+message_validator = TypeAdapter(UserMessage | AssistantMessage)
+
+SyncPromptResult = (
+    str | Message | dict[str, Any] | Sequence[str | Message | dict[str, Any]]
+)
+PromptResult = SyncPromptResult | Awaitable[SyncPromptResult]
+
+
+class PromptArgument(BaseModel):
+    """An argument that can be passed to a prompt."""
+
+    name: str = Field(description="Name of the argument")
+    description: str | None = Field(
+        None, description="Description of what the argument does"
+    )
+    required: bool = Field(
+        default=False, description="Whether the argument is required"
+    )
+
+
+class Prompt(BaseModel):
+    """A prompt template that can be rendered with parameters."""
+
+    name: str = Field(description="Name of the prompt")
+    description: str | None = Field(
+        None, description="Description of what the prompt does"
+    )
+    arguments: list[PromptArgument] | None = Field(
+        None, description="Arguments that can be passed to the prompt"
+    )
+    fn: Callable = Field(exclude=True)
+
+    @classmethod
+    def from_function(
+        cls,
+        fn: Callable[..., PromptResult],
+        name: str | None = None,
+        description: str | None = None,
+    ) -> "Prompt":
+        """Create a Prompt from a function.
+
+        The function can return:
+        - A string (converted to a message)
+        - A Message object
+        - A dict (converted to a message)
+        - A sequence of any of the above
+        """
+        func_name = name or fn.__name__
+
+        if func_name == "<lambda>":
+            raise ValueError("You must provide a name for lambda functions")
+
+        # Get schema from TypeAdapter - will fail if function isn't properly typed
+        parameters = TypeAdapter(fn).json_schema()
+
+        # Convert parameters to PromptArguments
+        arguments = []
+        if "properties" in parameters:
+            for param_name, param in parameters["properties"].items():
+                required = param_name in parameters.get("required", [])
+                arguments.append(
+                    PromptArgument(
+                        name=param_name,
+                        description=param.get("description"),
+                        required=required,
+                    )
+                )
+
+        # ensure the arguments are properly cast
+        fn = validate_call(fn)
+
+        return cls(
+            name=func_name,
+            description=description or fn.__doc__ or "",
+            arguments=arguments,
+            fn=fn,
+        )
+
+    async def render(self, arguments: dict[str, Any] | None = None) -> list[Message]:
+        """Render the prompt with arguments."""
+        # Validate required arguments
+        if self.arguments:
+            required = {arg.name for arg in self.arguments if arg.required}
+            provided = set(arguments or {})
+            missing = required - provided
+            if missing:
+                raise ValueError(f"Missing required arguments: {missing}")
+
+        try:
+            # Call function and check if result is a coroutine
+            result = self.fn(**(arguments or {}))
+            if inspect.iscoroutine(result):
+                result = await result
+
+            # Validate messages
+            if not isinstance(result, (list, tuple)):
+                result = [result]
+
+            # Convert result to messages
+            messages = []
+            for msg in result:
+                try:
+                    if isinstance(msg, Message):
+                        messages.append(msg)
+                    elif isinstance(msg, dict):
+                        msg = message_validator.validate_python(msg)
+                        messages.append(msg)
+                    elif isinstance(msg, str):
+                        messages.append(
+                            UserMessage(content=TextContent(type="text", text=msg))
+                        )
+                    else:
+                        msg = json.dumps(pydantic_core.to_jsonable_python(msg))
+                        messages.append(Message(role="user", content=msg))
+                except Exception:
+                    raise ValueError(
+                        f"Could not convert prompt result to message: {msg}"
+                    )
+
+            return messages
+        except Exception as e:
+            raise ValueError(f"Error rendering prompt {self.name}: {e}")

src/mcp/server/fastmcp/prompts/manager.py

@@ -0,0 +1,50 @@
+"""Prompt management functionality."""
+
+from typing import Any
+
+from mcp.server.fastmcp.prompts.base import Message, Prompt
+from mcp.server.fastmcp.utilities.logging import get_logger
+
+logger = get_logger(__name__)
+
+
+class PromptManager:
+    """Manages FastMCP prompts."""
+
+    def __init__(self, warn_on_duplicate_prompts: bool = True):
+        self._prompts: dict[str, Prompt] = {}
+        self.warn_on_duplicate_prompts = warn_on_duplicate_prompts
+
+    def get_prompt(self, name: str) -> Prompt | None:
+        """Get prompt by name."""
+        return self._prompts.get(name)
+
+    def list_prompts(self) -> list[Prompt]:
+        """List all registered prompts."""
+        return list(self._prompts.values())
+
+    def add_prompt(
+        self,
+        prompt: Prompt,
+    ) -> Prompt:
+        """Add a prompt to the manager."""
+
+        # Check for duplicates
+        existing = self._prompts.get(prompt.name)
+        if existing:
+            if self.warn_on_duplicate_prompts:
+                logger.warning(f"Prompt already exists: {prompt.name}")
+            return existing
+
+        self._prompts[prompt.name] = prompt
+        return prompt
+
+    async def render_prompt(
+        self, name: str, arguments: dict[str, Any] | None = None
+    ) -> list[Message]:
+        """Render a prompt by name with arguments."""
+        prompt = self.get_prompt(name)
+        if not prompt:
+            raise ValueError(f"Unknown prompt: {name}")
+
+        return await prompt.render(arguments)

src/mcp/server/fastmcp/prompts/prompt_manager.py

@@ -0,0 +1,33 @@
+"""Prompt management functionality."""
+
+from mcp.server.fastmcp.prompts.base import Prompt
+from mcp.server.fastmcp.utilities.logging import get_logger
+
+logger = get_logger(__name__)
+
+
+class PromptManager:
+    """Manages FastMCP prompts."""
+
+    def __init__(self, warn_on_duplicate_prompts: bool = True):
+        self._prompts: dict[str, Prompt] = {}
+        self.warn_on_duplicate_prompts = warn_on_duplicate_prompts
+
+    def add_prompt(self, prompt: Prompt) -> Prompt:
+        """Add a prompt to the manager."""
+        logger.debug(f"Adding prompt: {prompt.name}")
+        existing = self._prompts.get(prompt.name)
+        if existing:
+            if self.warn_on_duplicate_prompts:
+                logger.warning(f"Prompt already exists: {prompt.name}")
+            return existing
+        self._prompts[prompt.name] = prompt
+        return prompt
+
+    def get_prompt(self, name: str) -> Prompt | None:
+        """Get prompt by name."""
+        return self._prompts.get(name)
+
+    def list_prompts(self) -> list[Prompt]:
+        """List all registered prompts."""
+        return list(self._prompts.values())