145 lines
7.1 KiB
Python
145 lines
7.1 KiB
Python
"""Invariant tests: automatic Streamable HTTP -> SSE transport fallback (#53676, #104343).
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An SSE-only MCP server rejects the Streamable HTTP ``initialize`` POST (400-family status,
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or the SDK's opaque -32603 "Server returned an error response"); the client must retry over
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SSE on the initial connect only — never on reconnect after a proven session, never on
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timeout, and a both-transports failure must say so actionably.
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"""
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import asyncio
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import httpx
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import pytest
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from tools.mcp_tool import MCPServerTask
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def _http_400(status=400):
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request = httpx.Request("POST", "http://127.0.0.1:1/mcp")
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return httpx.HTTPStatusError("Bad Request", request=request,
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response=httpx.Response(status, request=request))
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class _SdkInternalError(Exception):
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"""Shape of mcp.shared.exceptions.MCPError for an opaque initialize rejection."""
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def __init__(self):
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super().__init__("Server returned an error response")
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self.error = type("E", (), {"code": -32603})()
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def _task(monkeypatch, http_exc, sse_result="shutdown", sse_exc=None):
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"""MCPServerTask whose transports are recorded fakes: HTTP raises, SSE serves or raises."""
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task = MCPServerTask("t")
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task._config = {}
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calls = []
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async def fake_serve(self, cm, label, timeout):
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calls.append(label)
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if label != "SSE":
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raise http_exc
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if sse_exc is not None:
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raise sse_exc
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self._ever_connected = True
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return sse_result
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monkeypatch.setattr(MCPServerTask, "_serve_transport", fake_serve)
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monkeypatch.setattr(MCPServerTask, "_streamable_http_transport", lambda self, *a, **k: object())
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monkeypatch.setattr(MCPServerTask, "_sse_transport", lambda self, *a, **k: object())
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monkeypatch.setattr(MCPServerTask, "_build_oauth_auth", lambda self, *a: None)
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return task, calls
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_CONFIG = {"url": "http://127.0.0.1:1/mcp", "connect_timeout": 1}
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@pytest.mark.parametrize("exc", [_http_400(), _http_400(405),
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ExceptionGroup("g", [_SdkInternalError()])])
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def test_sse_only_server_connects_via_fallback(monkeypatch, exc):
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"""Initial connect: a Streamable HTTP rejection falls back to SSE and serves; the latch
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routes subsequent reconnects straight to SSE without re-trying Streamable HTTP."""
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task, calls = _task(monkeypatch, exc)
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assert asyncio.run(task._run_http(dict(_CONFIG))) == "shutdown"
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assert calls[-1] == "SSE" and len(calls) == 2
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assert asyncio.run(task._run_http(dict(_CONFIG))) == "shutdown" # reconnect after latch
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assert calls[2:] == ["SSE"]
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@pytest.mark.parametrize("exc,ever_connected", [
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(_http_400(), True), # reconnect after a proven session: never mask the 400
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(TimeoutError(), False), # timeout is not a transport mismatch
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(_http_400(500), False), # 5xx is a broken server, not SSE-only
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])
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def test_no_fallback_on_reconnect_timeout_or_server_error(monkeypatch, exc, ever_connected):
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task, calls = _task(monkeypatch, exc)
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task._ever_connected = ever_connected
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with pytest.raises(type(exc)):
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asyncio.run(task._run_http(dict(_CONFIG)))
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assert "SSE" not in calls
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def test_both_transports_failing_names_both_and_suggests_config(monkeypatch):
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task, calls = _task(monkeypatch, _http_400(), sse_exc=ConnectionRefusedError("no sse"))
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with pytest.raises(ConnectionError, match="both Streamable HTTP and SSE.*transport: sse"):
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asyncio.run(task._run_http(dict(_CONFIG)))
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assert calls == ["HTTP", "SSE"] or calls == ["legacy HTTP", "SSE"]
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assert task._sse_fallback is False # failed fallback must not latch
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def test_opaque_sdk_rejection_is_reported_with_the_servers_status_and_body(monkeypatch, caplog):
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"""mcp >= 2.0 folds a non-JSON 4xx into ``-32603 Server returned an error response``; the
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warning and the both-transports ConnectionError must still name the HTTP status, the URL that
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was requested and the body the server sent (#114350, #113359). A root that already carries the
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status (httpx ``HTTPStatusError``) is left alone — no duplicated detail."""
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from tools.mcp_tool_errors import _make_http_rejection_recorder
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from tools.mcp_tool import sdk_httpx
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httpx2 = sdk_httpx()
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body = '{"jsonrpc":"2.0","error":{"code":-32020,"message":"Unsupported MCP-Protocol-Version"}}'
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async def _real_client_roundtrip(status, content_type):
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"""The recorder on a real SDK-httpx client, through the streaming API the SDK uses; the
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SDK's own later ``aread()`` must still see the bytes."""
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sink: dict = {}
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transport = httpx2.MockTransport(
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lambda req: httpx2.Response(status, text=body, headers={"content-type": content_type}))
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async with httpx2.AsyncClient(transport=transport, event_hooks={
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"response": [_make_http_rejection_recorder(sink)]}) as client:
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async with client.stream("POST", "http://127.0.0.1:1/mcp", json={}) as resp:
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assert (await resp.aread()).decode() == body
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return sink
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assert asyncio.run(_real_client_roundtrip(200, "application/json")) == {} # 2xx: nothing recorded
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recorded = asyncio.run(_real_client_roundtrip(400, "text/plain; charset=utf-8"))
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assert recorded == {"status": 400, "method": "POST", "url": "http://127.0.0.1:1/mcp", "body": body}
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def _connect_sees(rejection):
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task, _calls = _task(monkeypatch, ExceptionGroup("g", [_SdkInternalError()]),
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sse_exc=ConnectionRefusedError("no sse"))
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monkeypatch.setattr(MCPServerTask, "_streamable_http_transport",
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lambda self, *a, **k: self._http_rejection.update(rejection) or object())
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with pytest.raises(ConnectionError) as info:
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asyncio.run(task._run_http(dict(_CONFIG)))
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return str(info.value)
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with caplog.at_level("WARNING", logger="tools.mcp_tool"):
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message = _connect_sees(recorded)
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detail = "Server returned an error response (HTTP 400 from POST http://127.0.0.1:1/mcp: " + body + ")"
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assert detail in message and "SSE: no sse" in message
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assert any(detail in rec.getMessage() for rec in caplog.records), caplog.text
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# No rejection observed (the hook never fired): the SDK text stands alone, no fabricated detail.
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assert "Streamable HTTP: Server returned an error response; SSE" in _connect_sees({})
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def test_opaque_rejection_without_fallback_surfaces_the_status(monkeypatch):
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"""After a proven session the SSE fallback is off; the opaque SDK error still leaves ``_run_http``
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naming the recorded rejection instead of the bare ``Server returned an error response``."""
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task, calls = _task(monkeypatch, ExceptionGroup("g", [_SdkInternalError()]))
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task._ever_connected = True
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monkeypatch.setattr(MCPServerTask, "_streamable_http_transport", lambda self, *a, **k: self._http_rejection.update(
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status=503, method="POST", url="http://127.0.0.1:1/mcp", body="upstream down") or object())
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with pytest.raises(ConnectionError, match=r"HTTP 503 from POST http://127\.0\.0\.1:1/mcp: upstream down"):
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asyncio.run(task._run_http(dict(_CONFIG)))
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assert "SSE" not in calls
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