mirror of
https://github.com/aljazceru/mcp-python-sdk.git
synced 2025-12-19 14:54:24 +01:00
827e494df4
This commit adds support for request cancellation and tracking of in-flight requests in the MCP protocol implementation. The key architectural changes are: 1. Request Lifecycle Management: - Added _in_flight dictionary to BaseSession to track active requests - Requests are tracked from receipt until completion/cancellation - Added proper cleanup via on_complete callback 2. Cancellation Support: - Added CancelledNotification handling in _receive_loop - Implemented cancel() method in RequestResponder - Uses anyio.CancelScope for robust cancellation - Sends error response on cancellation 3. Request Context: - Added request_ctx ContextVar for request context - Ensures proper cleanup after request handling - Maintains request state throughout lifecycle 4. Error Handling: - Improved error propagation for cancelled requests - Added proper cleanup of cancelled requests - Maintains consistency of in-flight tracking This change enables clients to cancel long-running requests and servers to properly clean up resources when requests are cancelled. Github-Issue:#88
536 lines
19 KiB
Python
536 lines
19 KiB
Python
"""
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MCP Server Module
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This module provides a framework for creating an MCP (Model Context Protocol) server.
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It allows you to easily define and handle various types of requests and notifications
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in an asynchronous manner.
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Usage:
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1. Create a Server instance:
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server = Server("your_server_name")
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2. Define request handlers using decorators:
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@server.list_prompts()
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async def handle_list_prompts() -> list[types.Prompt]:
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# Implementation
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@server.get_prompt()
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async def handle_get_prompt(
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name: str, arguments: dict[str, str] | None
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) -> types.GetPromptResult:
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# Implementation
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@server.list_tools()
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async def handle_list_tools() -> list[types.Tool]:
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# Implementation
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@server.call_tool()
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async def handle_call_tool(
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name: str, arguments: dict | None
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) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
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# Implementation
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@server.list_resource_templates()
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async def handle_list_resource_templates() -> list[types.ResourceTemplate]:
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# Implementation
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3. Define notification handlers if needed:
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@server.progress_notification()
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async def handle_progress(
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progress_token: str | int, progress: float, total: float | None
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) -> None:
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# Implementation
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4. Run the server:
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async def main():
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async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
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await server.run(
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read_stream,
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write_stream,
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InitializationOptions(
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server_name="your_server_name",
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server_version="your_version",
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capabilities=server.get_capabilities(
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notification_options=NotificationOptions(),
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experimental_capabilities={},
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),
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),
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)
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asyncio.run(main())
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The Server class provides methods to register handlers for various MCP requests and
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notifications. It automatically manages the request context and handles incoming
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messages from the client.
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"""
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import contextvars
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import logging
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import warnings
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from collections.abc import Awaitable, Callable
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from typing import Any, Sequence
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from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
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from pydantic import AnyUrl
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import mcp.types as types
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from mcp.server.lowlevel.helper_types import ReadResourceContents
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from mcp.server.models import InitializationOptions
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from mcp.server.session import ServerSession
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from mcp.server.stdio import stdio_server as stdio_server
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from mcp.shared.context import RequestContext
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from mcp.shared.exceptions import McpError
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from mcp.shared.session import RequestResponder
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logger = logging.getLogger(__name__)
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request_ctx: contextvars.ContextVar[RequestContext[ServerSession]] = (
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contextvars.ContextVar("request_ctx")
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)
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class NotificationOptions:
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def __init__(
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self,
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prompts_changed: bool = False,
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resources_changed: bool = False,
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tools_changed: bool = False,
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):
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self.prompts_changed = prompts_changed
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self.resources_changed = resources_changed
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self.tools_changed = tools_changed
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class Server:
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def __init__(
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self, name: str, version: str | None = None, instructions: str | None = None
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):
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self.name = name
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self.version = version
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self.instructions = instructions
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self.request_handlers: dict[
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type, Callable[..., Awaitable[types.ServerResult]]
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] = {
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types.PingRequest: _ping_handler,
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}
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self.notification_handlers: dict[type, Callable[..., Awaitable[None]]] = {}
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self.notification_options = NotificationOptions()
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logger.debug(f"Initializing server '{name}'")
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def create_initialization_options(
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self,
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notification_options: NotificationOptions | None = None,
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experimental_capabilities: dict[str, dict[str, Any]] | None = None,
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) -> InitializationOptions:
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"""Create initialization options from this server instance."""
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def pkg_version(package: str) -> str:
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try:
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from importlib.metadata import version
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v = version(package)
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if v is not None:
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return v
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except Exception:
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pass
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return "unknown"
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return InitializationOptions(
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server_name=self.name,
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server_version=self.version if self.version else pkg_version("mcp"),
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capabilities=self.get_capabilities(
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notification_options or NotificationOptions(),
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experimental_capabilities or {},
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),
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instructions=self.instructions,
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)
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def get_capabilities(
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self,
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notification_options: NotificationOptions,
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experimental_capabilities: dict[str, dict[str, Any]],
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) -> types.ServerCapabilities:
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"""Convert existing handlers to a ServerCapabilities object."""
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prompts_capability = None
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resources_capability = None
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tools_capability = None
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logging_capability = None
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# Set prompt capabilities if handler exists
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if types.ListPromptsRequest in self.request_handlers:
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prompts_capability = types.PromptsCapability(
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listChanged=notification_options.prompts_changed
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)
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# Set resource capabilities if handler exists
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if types.ListResourcesRequest in self.request_handlers:
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resources_capability = types.ResourcesCapability(
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subscribe=False, listChanged=notification_options.resources_changed
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)
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# Set tool capabilities if handler exists
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if types.ListToolsRequest in self.request_handlers:
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tools_capability = types.ToolsCapability(
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listChanged=notification_options.tools_changed
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)
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# Set logging capabilities if handler exists
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if types.SetLevelRequest in self.request_handlers:
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logging_capability = types.LoggingCapability()
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return types.ServerCapabilities(
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prompts=prompts_capability,
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resources=resources_capability,
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tools=tools_capability,
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logging=logging_capability,
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experimental=experimental_capabilities,
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)
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@property
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def request_context(self) -> RequestContext[ServerSession]:
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"""If called outside of a request context, this will raise a LookupError."""
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return request_ctx.get()
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def list_prompts(self):
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def decorator(func: Callable[[], Awaitable[list[types.Prompt]]]):
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logger.debug("Registering handler for PromptListRequest")
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async def handler(_: Any):
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prompts = await func()
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return types.ServerResult(types.ListPromptsResult(prompts=prompts))
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self.request_handlers[types.ListPromptsRequest] = handler
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return func
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return decorator
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def get_prompt(self):
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def decorator(
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func: Callable[
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[str, dict[str, str] | None], Awaitable[types.GetPromptResult]
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],
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):
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logger.debug("Registering handler for GetPromptRequest")
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async def handler(req: types.GetPromptRequest):
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prompt_get = await func(req.params.name, req.params.arguments)
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return types.ServerResult(prompt_get)
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self.request_handlers[types.GetPromptRequest] = handler
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return func
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return decorator
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def list_resources(self):
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def decorator(func: Callable[[], Awaitable[list[types.Resource]]]):
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logger.debug("Registering handler for ListResourcesRequest")
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async def handler(_: Any):
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resources = await func()
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return types.ServerResult(
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types.ListResourcesResult(resources=resources)
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)
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self.request_handlers[types.ListResourcesRequest] = handler
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return func
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return decorator
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def list_resource_templates(self):
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def decorator(func: Callable[[], Awaitable[list[types.ResourceTemplate]]]):
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logger.debug("Registering handler for ListResourceTemplatesRequest")
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async def handler(_: Any):
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templates = await func()
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return types.ServerResult(
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types.ListResourceTemplatesResult(resourceTemplates=templates)
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)
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self.request_handlers[types.ListResourceTemplatesRequest] = handler
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return func
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return decorator
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def read_resource(self):
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def decorator(
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func: Callable[[AnyUrl], Awaitable[str | bytes | ReadResourceContents]],
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):
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logger.debug("Registering handler for ReadResourceRequest")
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async def handler(req: types.ReadResourceRequest):
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result = await func(req.params.uri)
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def create_content(data: str | bytes, mime_type: str | None):
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match data:
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case str() as data:
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return types.TextResourceContents(
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uri=req.params.uri,
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text=data,
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mimeType=mime_type or "text/plain",
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)
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case bytes() as data:
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import base64
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return types.BlobResourceContents(
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uri=req.params.uri,
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blob=base64.urlsafe_b64encode(data).decode(),
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mimeType=mime_type or "application/octet-stream",
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)
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match result:
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case str() | bytes() as data:
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warnings.warn(
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"Returning str or bytes from read_resource is deprecated. "
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"Use ReadResourceContents instead.",
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DeprecationWarning,
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stacklevel=2,
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)
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content = create_content(data, None)
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case ReadResourceContents() as contents:
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content = create_content(contents.content, contents.mime_type)
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case _:
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raise ValueError(
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f"Unexpected return type from read_resource: {type(result)}"
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)
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return types.ServerResult(
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types.ReadResourceResult(
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contents=[content],
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)
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)
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self.request_handlers[types.ReadResourceRequest] = handler
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return func
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return decorator
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def set_logging_level(self):
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def decorator(func: Callable[[types.LoggingLevel], Awaitable[None]]):
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logger.debug("Registering handler for SetLevelRequest")
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async def handler(req: types.SetLevelRequest):
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await func(req.params.level)
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return types.ServerResult(types.EmptyResult())
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self.request_handlers[types.SetLevelRequest] = handler
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return func
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return decorator
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def subscribe_resource(self):
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def decorator(func: Callable[[AnyUrl], Awaitable[None]]):
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logger.debug("Registering handler for SubscribeRequest")
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async def handler(req: types.SubscribeRequest):
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await func(req.params.uri)
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return types.ServerResult(types.EmptyResult())
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self.request_handlers[types.SubscribeRequest] = handler
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return func
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return decorator
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def unsubscribe_resource(self):
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def decorator(func: Callable[[AnyUrl], Awaitable[None]]):
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logger.debug("Registering handler for UnsubscribeRequest")
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async def handler(req: types.UnsubscribeRequest):
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await func(req.params.uri)
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return types.ServerResult(types.EmptyResult())
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self.request_handlers[types.UnsubscribeRequest] = handler
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return func
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return decorator
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def list_tools(self):
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def decorator(func: Callable[[], Awaitable[list[types.Tool]]]):
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logger.debug("Registering handler for ListToolsRequest")
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async def handler(_: Any):
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tools = await func()
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return types.ServerResult(types.ListToolsResult(tools=tools))
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self.request_handlers[types.ListToolsRequest] = handler
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return func
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return decorator
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def call_tool(self):
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def decorator(
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func: Callable[
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...,
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Awaitable[
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Sequence[
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types.TextContent | types.ImageContent | types.EmbeddedResource
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]
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],
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],
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):
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logger.debug("Registering handler for CallToolRequest")
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async def handler(req: types.CallToolRequest):
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try:
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results = await func(req.params.name, (req.params.arguments or {}))
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return types.ServerResult(
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types.CallToolResult(content=list(results), isError=False)
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)
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except Exception as e:
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return types.ServerResult(
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types.CallToolResult(
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content=[types.TextContent(type="text", text=str(e))],
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isError=True,
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)
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)
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self.request_handlers[types.CallToolRequest] = handler
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return func
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return decorator
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def progress_notification(self):
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def decorator(
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func: Callable[[str | int, float, float | None], Awaitable[None]],
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):
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logger.debug("Registering handler for ProgressNotification")
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async def handler(req: types.ProgressNotification):
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await func(
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req.params.progressToken, req.params.progress, req.params.total
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)
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self.notification_handlers[types.ProgressNotification] = handler
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return func
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return decorator
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def completion(self):
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"""Provides completions for prompts and resource templates"""
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def decorator(
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func: Callable[
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[
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types.PromptReference | types.ResourceReference,
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types.CompletionArgument,
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],
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Awaitable[types.Completion | None],
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],
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):
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logger.debug("Registering handler for CompleteRequest")
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async def handler(req: types.CompleteRequest):
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completion = await func(req.params.ref, req.params.argument)
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return types.ServerResult(
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types.CompleteResult(
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completion=completion
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if completion is not None
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else types.Completion(values=[], total=None, hasMore=None),
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)
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)
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self.request_handlers[types.CompleteRequest] = handler
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return func
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return decorator
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async def run(
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self,
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read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
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write_stream: MemoryObjectSendStream[types.JSONRPCMessage],
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initialization_options: InitializationOptions,
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# When False, exceptions are returned as messages to the client.
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# When True, exceptions are raised, which will cause the server to shut down
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# but also make tracing exceptions much easier during testing and when using
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# in-process servers.
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raise_exceptions: bool = False,
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):
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with warnings.catch_warnings(record=True) as w:
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async with ServerSession(
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read_stream, write_stream, initialization_options
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) as session:
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async for message in session.incoming_messages:
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logger.debug(f"Received message: {message}")
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match message:
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case (
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RequestResponder(
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request=types.ClientRequest(root=req)
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) as responder
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):
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with responder:
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await self._handle_request(
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message, req, session, raise_exceptions
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)
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case types.ClientNotification(root=notify):
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await self._handle_notification(notify)
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for warning in w:
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logger.info(
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f"Warning: {warning.category.__name__}: {warning.message}"
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)
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async def _handle_request(
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self,
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message: RequestResponder,
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req: Any,
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session: ServerSession,
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raise_exceptions: bool,
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):
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logger.info(f"Processing request of type {type(req).__name__}")
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if type(req) in self.request_handlers:
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handler = self.request_handlers[type(req)]
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logger.debug(f"Dispatching request of type {type(req).__name__}")
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token = None
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try:
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# Set our global state that can be retrieved via
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# app.get_request_context()
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token = request_ctx.set(
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RequestContext(
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message.request_id,
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message.request_meta,
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session,
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)
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)
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response = await handler(req)
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except McpError as err:
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response = err.error
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except Exception as err:
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if raise_exceptions:
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raise err
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response = types.ErrorData(code=0, message=str(err), data=None)
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finally:
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# Reset the global state after we are done
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if token is not None:
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request_ctx.reset(token)
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await message.respond(response)
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else:
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await message.respond(
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types.ErrorData(
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code=types.METHOD_NOT_FOUND,
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message="Method not found",
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)
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)
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logger.debug("Response sent")
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async def _handle_notification(self, notify: Any):
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if type(notify) in self.notification_handlers:
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assert type(notify) in self.notification_handlers
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handler = self.notification_handlers[type(notify)]
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logger.debug(
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f"Dispatching notification of type " f"{type(notify).__name__}"
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)
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try:
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await handler(notify)
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except Exception as err:
|
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logger.error(f"Uncaught exception in notification handler: " f"{err}")
|
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|
|
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async def _ping_handler(request: types.PingRequest) -> types.ServerResult:
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return types.ServerResult(types.EmptyResult())
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