server_lowlevel.py

"""One lowlevel Server factory that serves both the 2025 handshake era and the 2026 stateless era."""

from typing import Any

import mcp_types as types
from mcp_types.version import MODERN_PROTOCOL_VERSIONS

from mcp.server.context import ServerRequestContext
from mcp.server.lowlevel import Server
from stories._hosting import run_server_from_args

GREET_INPUT_SCHEMA: dict[str, Any] = {
    "type": "object",
    "properties": {"name": {"type": "string"}},
    "required": ["name"],
}


def build_server() -> Server[Any]:
    async def list_tools(
        ctx: ServerRequestContext[Any], params: types.PaginatedRequestParams | None
    ) -> types.ListToolsResult:
        return types.ListToolsResult(
            tools=[
                types.Tool(
                    name="greet",
                    description="Greet the caller and report which protocol era served the request.",
                    input_schema=GREET_INPUT_SCHEMA,
                ),
            ]
        )

    async def call_tool(ctx: ServerRequestContext[Any], params: types.CallToolRequestParams) -> types.CallToolResult:
        assert params.name == "greet" and params.arguments is not None
        era = "modern" if ctx.protocol_version in MODERN_PROTOCOL_VERSIONS else "legacy"
        text = f"Hello, {params.arguments['name']}! (served on the {era} era at {ctx.protocol_version})"
        return types.CallToolResult(content=[types.TextContent(text=text)])

    # The same factory serves both eras with no configuration. Which era a request is
    # on is decided by the entry point / transport, never by the server.
    return Server(
        "dual-era-example",
        instructions="A small dual-era demo server.",
        on_list_tools=list_tools,
        on_call_tool=call_tool,
    )


if __name__ == "__main__":
    run_server_from_args(build_server)