|
| 1 | +from __future__ import annotations |
| 2 | + |
| 3 | +import abc |
| 4 | +import asyncio |
| 5 | +from contextlib import AbstractAsyncContextManager, AsyncExitStack |
| 6 | +from pathlib import Path |
| 7 | +from typing import Any, Literal |
| 8 | + |
| 9 | +from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream |
| 10 | +from mcp import ClientSession, StdioServerParameters, Tool as MCPTool, stdio_client |
| 11 | +from mcp.client.sse import sse_client |
| 12 | +from mcp.types import CallToolResult, JSONRPCMessage |
| 13 | +from typing_extensions import NotRequired, TypedDict |
| 14 | + |
| 15 | +from ..exceptions import UserError |
| 16 | +from ..logger import logger |
| 17 | + |
| 18 | + |
| 19 | +class MCPServer(abc.ABC): |
| 20 | + """Base class for Model Context Protocol servers.""" |
| 21 | + |
| 22 | + @abc.abstractmethod |
| 23 | + async def connect(self): |
| 24 | + """Connect to the server. For example, this might mean spawning a subprocess or |
| 25 | + opening a network connection. The server is expected to remain connected until |
| 26 | + `cleanup()` is called. |
| 27 | + """ |
| 28 | + pass |
| 29 | + |
| 30 | + @abc.abstractmethod |
| 31 | + async def cleanup(self): |
| 32 | + """Cleanup the server. For example, this might mean closing a subprocess or |
| 33 | + closing a network connection. |
| 34 | + """ |
| 35 | + pass |
| 36 | + |
| 37 | + @abc.abstractmethod |
| 38 | + async def list_tools(self) -> list[MCPTool]: |
| 39 | + """List the tools available on the server.""" |
| 40 | + pass |
| 41 | + |
| 42 | + @abc.abstractmethod |
| 43 | + async def call_tool(self, tool_name: str, arguments: dict[str, Any] | None) -> CallToolResult: |
| 44 | + """Invoke a tool on the server.""" |
| 45 | + pass |
| 46 | + |
| 47 | + |
| 48 | +class _MCPServerWithClientSession(MCPServer, abc.ABC): |
| 49 | + """Base class for MCP servers that use a `ClientSession` to communicate with the server.""" |
| 50 | + |
| 51 | + def __init__(self, cache_tools_list: bool): |
| 52 | + """ |
| 53 | + Args: |
| 54 | + cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be |
| 55 | + cached and only fetched from the server once. If `False`, the tools list will be |
| 56 | + fetched from the server on each call to `list_tools()`. The cache can be invalidated |
| 57 | + by calling `invalidate_tools_cache()`. You should set this to `True` if you know the |
| 58 | + server will not change its tools list, because it can drastically improve latency |
| 59 | + (by avoiding a round-trip to the server every time). |
| 60 | + """ |
| 61 | + self.session: ClientSession | None = None |
| 62 | + self.exit_stack: AsyncExitStack = AsyncExitStack() |
| 63 | + self._cleanup_lock: asyncio.Lock = asyncio.Lock() |
| 64 | + self.cache_tools_list = cache_tools_list |
| 65 | + |
| 66 | + # The cache is always dirty at startup, so that we fetch tools at least once |
| 67 | + self._cache_dirty = True |
| 68 | + self._tools_list: list[MCPTool] | None = None |
| 69 | + |
| 70 | + @abc.abstractmethod |
| 71 | + def create_streams( |
| 72 | + self, |
| 73 | + ) -> AbstractAsyncContextManager[ |
| 74 | + tuple[ |
| 75 | + MemoryObjectReceiveStream[JSONRPCMessage | Exception], |
| 76 | + MemoryObjectSendStream[JSONRPCMessage], |
| 77 | + ] |
| 78 | + ]: |
| 79 | + """Create the streams for the server.""" |
| 80 | + pass |
| 81 | + |
| 82 | + async def __aenter__(self): |
| 83 | + await self.connect() |
| 84 | + return self |
| 85 | + |
| 86 | + async def __aexit__(self, exc_type, exc_value, traceback): |
| 87 | + await self.cleanup() |
| 88 | + |
| 89 | + def invalidate_tools_cache(self): |
| 90 | + """Invalidate the tools cache.""" |
| 91 | + self._cache_dirty = True |
| 92 | + |
| 93 | + async def connect(self): |
| 94 | + """Connect to the server.""" |
| 95 | + try: |
| 96 | + transport = await self.exit_stack.enter_async_context(self.create_streams()) |
| 97 | + read, write = transport |
| 98 | + session = await self.exit_stack.enter_async_context(ClientSession(read, write)) |
| 99 | + await session.initialize() |
| 100 | + self.session = session |
| 101 | + except Exception as e: |
| 102 | + logger.error(f"Error initializing MCP server: {e}") |
| 103 | + await self.cleanup() |
| 104 | + raise |
| 105 | + |
| 106 | + async def list_tools(self) -> list[MCPTool]: |
| 107 | + """List the tools available on the server.""" |
| 108 | + if not self.session: |
| 109 | + raise UserError("Server not initialized. Make sure you call `connect()` first.") |
| 110 | + |
| 111 | + # Return from cache if caching is enabled, we have tools, and the cache is not dirty |
| 112 | + if self.cache_tools_list and not self._cache_dirty and self._tools_list: |
| 113 | + return self._tools_list |
| 114 | + |
| 115 | + # Reset the cache dirty to False |
| 116 | + self._cache_dirty = False |
| 117 | + |
| 118 | + # Fetch the tools from the server |
| 119 | + self._tools_list = (await self.session.list_tools()).tools |
| 120 | + return self._tools_list |
| 121 | + |
| 122 | + async def call_tool(self, tool_name: str, arguments: dict[str, Any] | None) -> CallToolResult: |
| 123 | + """Invoke a tool on the server.""" |
| 124 | + if not self.session: |
| 125 | + raise UserError("Server not initialized. Make sure you call `connect()` first.") |
| 126 | + |
| 127 | + return await self.session.call_tool(tool_name, arguments) |
| 128 | + |
| 129 | + async def cleanup(self): |
| 130 | + """Cleanup the server.""" |
| 131 | + async with self._cleanup_lock: |
| 132 | + try: |
| 133 | + await self.exit_stack.aclose() |
| 134 | + self.session = None |
| 135 | + except Exception as e: |
| 136 | + logger.error(f"Error cleaning up server: {e}") |
| 137 | + |
| 138 | + |
| 139 | +class MCPServerStdioParams(TypedDict): |
| 140 | + """Mirrors `mcp.client.stdio.StdioServerParameters`, but lets you pass params without another |
| 141 | + import. |
| 142 | + """ |
| 143 | + |
| 144 | + command: str |
| 145 | + """The executable to run to start the server. For example, `python` or `node`.""" |
| 146 | + |
| 147 | + args: NotRequired[list[str]] |
| 148 | + """Command line args to pass to the `command` executable. For example, `['foo.py']` or |
| 149 | + `['server.js', '--port', '8080']`.""" |
| 150 | + |
| 151 | + env: NotRequired[dict[str, str]] |
| 152 | + """The environment variables to set for the server. .""" |
| 153 | + |
| 154 | + cwd: NotRequired[str | Path] |
| 155 | + """The working directory to use when spawning the process.""" |
| 156 | + |
| 157 | + encoding: NotRequired[str] |
| 158 | + """The text encoding used when sending/receiving messages to the server. Defaults to `utf-8`.""" |
| 159 | + |
| 160 | + encoding_error_handler: NotRequired[Literal["strict", "ignore", "replace"]] |
| 161 | + """The text encoding error handler. Defaults to `strict`. |
| 162 | +
|
| 163 | + See https://docs.python.org/3/library/codecs.html#codec-base-classes for |
| 164 | + explanations of possible values. |
| 165 | + """ |
| 166 | + |
| 167 | + |
| 168 | +class MCPServerStdio(_MCPServerWithClientSession): |
| 169 | + """MCP server implementation that uses the stdio transport. See the [spec] |
| 170 | + (https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#stdio) for |
| 171 | + details. |
| 172 | + """ |
| 173 | + |
| 174 | + def __init__(self, params: MCPServerStdioParams, cache_tools_list: bool = False): |
| 175 | + """Create a new MCP server based on the stdio transport. |
| 176 | +
|
| 177 | + Args: |
| 178 | + params: The params that configure the server. This includes: |
| 179 | + - The command (e.g. `python` or `node`) that starts the server. |
| 180 | + - The args to pass to the server command (e.g. `foo.py` or `server.js`). |
| 181 | + - The environment variables to set for the server. |
| 182 | + cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be |
| 183 | + cached and only fetched from the server once. If `False`, the tools list will be |
| 184 | + fetched from the server on each call to `list_tools()`. The cache can be |
| 185 | + invalidated by calling `invalidate_tools_cache()`. You should set this to `True` |
| 186 | + if you know the server will not change its tools list, because it can drastically |
| 187 | + improve latency (by avoiding a round-trip to the server every time). |
| 188 | + """ |
| 189 | + super().__init__(cache_tools_list) |
| 190 | + |
| 191 | + self.params = StdioServerParameters( |
| 192 | + command=params["command"], |
| 193 | + args=params.get("args", []), |
| 194 | + env=params.get("env"), |
| 195 | + cwd=params.get("cwd"), |
| 196 | + encoding=params.get("encoding", "utf-8"), |
| 197 | + encoding_error_handler=params.get("encoding_error_handler", "strict"), |
| 198 | + ) |
| 199 | + |
| 200 | + def create_streams( |
| 201 | + self, |
| 202 | + ) -> AbstractAsyncContextManager[ |
| 203 | + tuple[ |
| 204 | + MemoryObjectReceiveStream[JSONRPCMessage | Exception], |
| 205 | + MemoryObjectSendStream[JSONRPCMessage], |
| 206 | + ] |
| 207 | + ]: |
| 208 | + """Create the streams for the server.""" |
| 209 | + return stdio_client(self.params) |
| 210 | + |
| 211 | + |
| 212 | +class MCPServerSseParams(TypedDict): |
| 213 | + """Mirrors the params in`mcp.client.sse.sse_client`.""" |
| 214 | + |
| 215 | + url: str |
| 216 | + """The URL of the server.""" |
| 217 | + |
| 218 | + headers: NotRequired[dict[str, str]] |
| 219 | + """The headers to send to the server.""" |
| 220 | + |
| 221 | + timeout: NotRequired[float] |
| 222 | + """The timeout for the HTTP request. Defaults to 5 seconds.""" |
| 223 | + |
| 224 | + sse_read_timeout: NotRequired[float] |
| 225 | + """The timeout for the SSE connection, in seconds. Defaults to 5 minutes.""" |
| 226 | + |
| 227 | + |
| 228 | +class MCPServerSse(_MCPServerWithClientSession): |
| 229 | + """MCP server implementation that uses the HTTP with SSE transport. See the [spec] |
| 230 | + (https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#http-with-sse) |
| 231 | + for details. |
| 232 | + """ |
| 233 | + |
| 234 | + def __init__(self, params: MCPServerSseParams, cache_tools_list: bool = False): |
| 235 | + """Create a new MCP server based on the HTTP with SSE transport. |
| 236 | +
|
| 237 | + Args: |
| 238 | + params: The params that configure the server. This includes: |
| 239 | + - The URL of the server. |
| 240 | + - The headers to send to the server. |
| 241 | + - The timeout for the HTTP request. |
| 242 | + - The timeout for the SSE connection. |
| 243 | +
|
| 244 | + cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be |
| 245 | + cached and only fetched from the server once. If `False`, the tools list will be |
| 246 | + fetched from the server on each call to `list_tools()`. The cache can be |
| 247 | + invalidated by calling `invalidate_tools_cache()`. You should set this to `True` |
| 248 | + if you know the server will not change its tools list, because it can drastically |
| 249 | + improve latency (by avoiding a round-trip to the server every time). |
| 250 | + """ |
| 251 | + super().__init__(cache_tools_list) |
| 252 | + |
| 253 | + self.params = params |
| 254 | + |
| 255 | + def create_streams( |
| 256 | + self, |
| 257 | + ) -> AbstractAsyncContextManager[ |
| 258 | + tuple[ |
| 259 | + MemoryObjectReceiveStream[JSONRPCMessage | Exception], |
| 260 | + MemoryObjectSendStream[JSONRPCMessage], |
| 261 | + ] |
| 262 | + ]: |
| 263 | + """Create the streams for the server.""" |
| 264 | + return sse_client( |
| 265 | + url=self.params["url"], |
| 266 | + headers=self.params.get("headers", None), |
| 267 | + timeout=self.params.get("timeout", 5), |
| 268 | + sse_read_timeout=self.params.get("sse_read_timeout", 60 * 5), |
| 269 | + ) |
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