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Stabilize quarantined real-MCP redirect diagnostic for non-redirecting /mcp servers #2

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Stabilize quarantined real-MCP redirect diagnostic for non-redirecting /mcp servers #2

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e87c3ec
Initial plan
Copilot Sep 25, 2026
6715c5f
test: tolerate non-redirecting /mcp in real-MCP diagnostic
Copilot Sep 25, 2026
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34 changes: 28 additions & 6 deletions tests/test_downstream_remote_paths.py
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Original file line number Diff line number Diff line change
Expand Up @@ -301,13 +301,11 @@ async def test_unreachable_downstream_fails_fast_instead_of_hanging() -> None:


async def test_factory_follows_the_mcp_trailing_slash_redirect() -> None:
"""The MCP POST to ``/mcp`` is answered with a 307 to ``/mcp/``.
"""If ``/mcp`` redirects to ``/mcp/``, the factory must survive it.

An explicitly configured ``httpx.AsyncClient`` does NOT follow redirects by
default, so the factory has to opt in or every ordinary MCP mount breaks.
Proven behaviourally rather than by probing a status code: a client with
redirects disabled fails, the factory's client succeeds against the same
server.
Some Streamable-HTTP servers redirect ``/mcp`` to ``/mcp/`` while others
now serve ``/mcp`` directly. This diagnostic only applies to redirecting
servers.
"""
from mcp import ClientSession
from mcp.client.streamable_http import streamable_http_client
Expand All @@ -316,6 +314,30 @@ async def test_factory_follows_the_mcp_trailing_slash_redirect() -> None:
async with AsyncExitStack() as stack:
srv = await stack.enter_async_context(_Server(servers["records"]))

probe_payload = {
"jsonrpc": "2.0",
"id": 1,
"method": "initialize",
"params": {
"protocolVersion": "2025-06-18",
"capabilities": {},
"clientInfo": {"name": "probe", "version": "0"},
},
}
async with httpx.AsyncClient(
timeout=httpx.Timeout(None, connect=10.0), follow_redirects=False
) as probe:
probe_resp = await probe.post(
srv.url,
json=probe_payload,
headers={"accept": "application/json, text/event-stream"},
)
if probe_resp.status_code not in (307, 308):
pytest.skip(
f"server does not redirect /mcp (got {probe_resp.status_code}); "
"redirect diagnostic not applicable"
)

# Redirects disabled → the handshake cannot complete.
with pytest.raises((httpx.HTTPStatusError, ExceptionGroup)) as err:
async with httpx.AsyncClient(
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