mcp-python-sdk/tests/shared/test_sse.py

import multiprocessing
import socket
import time
import anyio
from starlette.requests import Request
import uvicorn
import pytest
from pydantic import AnyUrl
import httpx
from typing import AsyncGenerator, Generator
from starlette.applications import Starlette
from starlette.routing import Mount, Route

from mcp.shared.exceptions import McpError
from mcp.client.session import ClientSession
from mcp.client.sse import sse_client
from mcp.server import Server
from mcp.server.sse import SseServerTransport
from mcp.types import (
    EmptyResult,
    ErrorData,
    InitializeResult,
    TextContent,
    TextResourceContents,
    Tool,
)

SERVER_NAME = "test_server_for_SSE"


@pytest.fixture
def server_port() -> int:
    with socket.socket() as s:
        s.bind(("127.0.0.1", 0))
        return s.getsockname()[1]


@pytest.fixture
def server_url(server_port: int) -> str:
    return f"http://127.0.0.1:{server_port}"


# Test server implementation
class TestServer(Server):
    def __init__(self):
        super().__init__(SERVER_NAME)

        @self.read_resource()
        async def handle_read_resource(uri: AnyUrl) -> str | bytes:
            if uri.scheme == "foobar":
                return f"Read {uri.host}"
            # TODO: make this an error
            raise McpError(
                error=ErrorData(
                    code=404, message="OOPS! no resource with that URI was found"
                )
            )

        @self.list_tools()
        async def handle_list_tools() -> list[Tool]:
            return [
                Tool(
                    name="test_tool",
                    description="A test tool",
                    inputSchema={"type": "object", "properties": {}},
                )
            ]

        @self.call_tool()
        async def handle_call_tool(name: str, args: dict) -> list[TextContent]:
            return [TextContent(type="text", text=f"Called {name}")]


# Test fixtures
def make_server_app() -> Starlette:
    """Create test Starlette app with SSE transport"""
    sse = SseServerTransport("/messages/")
    server = TestServer()

    async def handle_sse(request: Request) -> None:
        async with sse.connect_sse(
            request.scope, request.receive, request._send
        ) as streams:
            await server.run(
                streams[0], streams[1], server.create_initialization_options()
            )

    app = Starlette(
        routes=[
            Route("/sse", endpoint=handle_sse),
            Mount("/messages/", app=sse.handle_post_message),
        ]
    )

    return app


def run_server(server_port: int) -> None:
    app = make_server_app()
    server = uvicorn.Server(
        config=uvicorn.Config(
            app=app, host="127.0.0.1", port=server_port, log_level="error"
        )
    )
    print(f"starting server on {server_port}")
    server.run()

    # Give server time to start
    while not server.started:
        print("waiting for server to start")
        time.sleep(0.5)


@pytest.fixture()
def server(server_port: int) -> Generator[None, None, None]:
    proc = multiprocessing.Process(
        target=run_server, kwargs={"server_port": server_port}, daemon=True
    )
    print("starting process")
    proc.start()

    # Wait for server to be running
    max_attempts = 20
    attempt = 0
    print("waiting for server to start")
    while attempt < max_attempts:
        try:
            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
                s.connect(("127.0.0.1", server_port))
                break
        except ConnectionRefusedError:
            time.sleep(0.1)
            attempt += 1
    else:
        raise RuntimeError(
            "Server failed to start after {} attempts".format(max_attempts)
        )

    yield

    print("killing server")
    # Signal the server to stop
    proc.kill()
    proc.join(timeout=2)
    if proc.is_alive():
        print("server process failed to terminate")


@pytest.fixture()
async def http_client(server, server_url) -> AsyncGenerator[httpx.AsyncClient, None]:
    """Create test client"""
    async with httpx.AsyncClient(base_url=server_url) as client:
        yield client


# Tests
@pytest.mark.anyio
async def test_raw_sse_connection(http_client: httpx.AsyncClient) -> None:
    """Test the SSE connection establishment simply with an HTTP client."""
    async with anyio.create_task_group() as tg:

        async def connection_test() -> None:
            async with http_client.stream("GET", "/sse") as response:
                assert response.status_code == 200
                assert (
                    response.headers["content-type"]
                    == "text/event-stream; charset=utf-8"
                )

                line_number = 0
                async for line in response.aiter_lines():
                    if line_number == 0:
                        assert line == "event: endpoint"
                    elif line_number == 1:
                        assert line.startswith("data: /messages/?session_id=")
                    else:
                        return
                    line_number += 1

        # Add timeout to prevent test from hanging if it fails
        with anyio.fail_after(3):
            await connection_test()


@pytest.mark.anyio
async def test_sse_client_basic_connection(server: None, server_url: str) -> None:
    async with sse_client(server_url + "/sse") as streams:
        async with ClientSession(*streams) as session:
            # Test initialization
            result = await session.initialize()
            assert isinstance(result, InitializeResult)
            assert result.serverInfo.name == SERVER_NAME

            # Test ping
            ping_result = await session.send_ping()
            assert isinstance(ping_result, EmptyResult)


@pytest.fixture
async def initialized_sse_client_session(
    server, server_url: str
) -> AsyncGenerator[ClientSession, None]:
    async with sse_client(server_url + "/sse") as streams:
        async with ClientSession(*streams) as session:
            await session.initialize()
            yield session


@pytest.mark.anyio
async def test_sse_client_happy_request_and_response(
    initialized_sse_client_session: ClientSession,
) -> None:
    session = initialized_sse_client_session
    response = await session.read_resource(uri=AnyUrl("foobar://should-work"))
    assert len(response.contents) == 1
    assert isinstance(response.contents[0], TextResourceContents)
    assert response.contents[0].text == "Read should-work"


@pytest.mark.anyio
async def test_sse_client_exception_handling(
    initialized_sse_client_session: ClientSession,
) -> None:
    session = initialized_sse_client_session
    with pytest.raises(McpError, match="OOPS! no resource with that URI was found"):
        await session.read_resource(uri=AnyUrl("xxx://will-not-work"))


# TODO: test that timeouts are respected and that the error comes back