test_sse.py

import multiprocessing
import socket
import time
from collections.abc import AsyncGenerator, Generator

import anyio
import httpx
import pytest
import uvicorn
from pydantic import AnyUrl
from starlette.applications import Starlette
from starlette.requests import Request
from starlette.routing import Mount, Route

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.shared.exceptions import McpError
from mcp.types import (
    EmptyResult,
    ErrorData,
    InitializeResult,
    ReadResourceResult,
    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 ServerTest(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}"
            elif uri.scheme == "slow":
                # Simulate a slow resource
                await anyio.sleep(2.0)
                return f"Slow response from {uri.host}"

            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 = ServerTest()

    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(f"Server failed to start after {max_attempts} 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():

        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", sse_read_timeout=0.5) 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"))


@pytest.mark.anyio
@pytest.mark.skip(
    "this test highlights a possible bug in SSE read timeout exception handling"
)
async def test_sse_client_timeout(
    initialized_sse_client_session: ClientSession,
) -> None:
    session = initialized_sse_client_session

    # sanity check that normal, fast responses are working
    response = await session.read_resource(uri=AnyUrl("foobar://1"))
    assert isinstance(response, ReadResourceResult)

    with anyio.move_on_after(3):
        with pytest.raises(McpError, match="Read timed out"):
            response = await session.read_resource(uri=AnyUrl("slow://2"))
            # we should receive an error here
        return

    pytest.fail("the client should have timed out and returned an error already")