1"""Lightweight connection handling for MCP servers."""
2 
3from abc import ABC, abstractmethod
4from contextlib import AsyncExitStack
5from typing import Any
6 
7from mcp import ClientSession, StdioServerParameters
8from mcp.client.sse import sse_client
9from mcp.client.stdio import stdio_client
10from mcp.client.streamable_http import streamablehttp_client
11 
12 
13class MCPConnection(ABC):
14    """Base class for MCP server connections."""
15 
16    def __init__(self):
17        self.session = None
18        self._stack = None
19 
20    @abstractmethod
21    def _create_context(self):
22        """Create the connection context based on connection type."""
23 
24    async def __aenter__(self):
25        """Initialize MCP server connection."""
26        self._stack = AsyncExitStack()
27        await self._stack.__aenter__()
28 
29        try:
30            ctx = self._create_context()
31            result = await self._stack.enter_async_context(ctx)
32 
33            if len(result) == 2:
34                read, write = result
35            elif len(result) == 3:
36                read, write, _ = result
37            else:
38                raise ValueError(f"Unexpected context result: {result}")
39 
40            session_ctx = ClientSession(read, write)
41            self.session = await self._stack.enter_async_context(session_ctx)
42            await self.session.initialize()
43            return self
44        except BaseException:
45            await self._stack.__aexit__(None, None, None)
46            raise
47 
48    async def __aexit__(self, exc_type, exc_val, exc_tb):
49        """Clean up MCP server connection resources."""
50        if self._stack:
51            await self._stack.__aexit__(exc_type, exc_val, exc_tb)
52        self.session = None
53        self._stack = None
54 
55    async def list_tools(self) -> list[dict[str, Any]]:
56        """Retrieve available tools from the MCP server."""
57        response = await self.session.list_tools()
58        return [
59            {
60                "name": tool.name,
61                "description": tool.description,
62                "input_schema": tool.inputSchema,
63            }
64            for tool in response.tools
65        ]
66 
67    async def call_tool(self, tool_name: str, arguments: dict[str, Any]) -> Any:
68        """Call a tool on the MCP server with provided arguments."""
69        result = await self.session.call_tool(tool_name, arguments=arguments)
70        return result.content
71 
72 
73class MCPConnectionStdio(MCPConnection):
74    """MCP connection using standard input/output."""
75 
76    def __init__(self, command: str, args: list[str] = None, env: dict[str, str] = None):
77        super().__init__()
78        self.command = command
79        self.args = args or []
80        self.env = env
81 
82    def _create_context(self):
83        return stdio_client(
84            StdioServerParameters(command=self.command, args=self.args, env=self.env)
85        )
86 
87 
88class MCPConnectionSSE(MCPConnection):
89    """MCP connection using Server-Sent Events."""
90 
91    def __init__(self, url: str, headers: dict[str, str] = None):
92        super().__init__()
93        self.url = url
94        self.headers = headers or {}
95 
96    def _create_context(self):
97        return sse_client(url=self.url, headers=self.headers)
98 
99 
100class MCPConnectionHTTP(MCPConnection):
101    """MCP connection using Streamable HTTP."""
102 
103    def __init__(self, url: str, headers: dict[str, str] = None):
104        super().__init__()
105        self.url = url
106        self.headers = headers or {}
107 
108    def _create_context(self):
109        return streamablehttp_client(url=self.url, headers=self.headers)
110 
111 
112def create_connection(
113    transport: str,
114    command: str = None,
115    args: list[str] = None,
116    env: dict[str, str] = None,
117    url: str = None,
118    headers: dict[str, str] = None,
119) -> MCPConnection:
120    """Factory function to create the appropriate MCP connection.
121 
122    Args:
123        transport: Connection type ("stdio", "sse", or "http")
124        command: Command to run (stdio only)
125        args: Command arguments (stdio only)
126        env: Environment variables (stdio only)
127        url: Server URL (sse and http only)
128        headers: HTTP headers (sse and http only)
129 
130    Returns:
131        MCPConnection instance
132    """
133    transport = transport.lower()
134 
135    if transport == "stdio":
136        if not command:
137            raise ValueError("Command is required for stdio transport")
138        return MCPConnectionStdio(command=command, args=args, env=env)
139 
140    elif transport == "sse":
141        if not url:
142            raise ValueError("URL is required for sse transport")
143        return MCPConnectionSSE(url=url, headers=headers)
144 
145    elif transport in ["http", "streamable_http", "streamable-http"]:
146        if not url:
147            raise ValueError("URL is required for http transport")
148        return MCPConnectionHTTP(url=url, headers=headers)
149 
150    else:
151        raise ValueError(f"Unsupported transport type: {transport}. Use 'stdio', 'sse', or 'http'")
152