fix(streamable-http): downgrade stateless 'Terminating session: None' log

In stateless mode every request created a transport with mcp_session_id=None
and terminated it on completion, producing
'INFO: Terminating session: None' on every request. The repeated noise made
real session terminations hard to find and confused users into thinking
their connection was dropping.

Branch on mcp_session_id in terminate(): keep the existing INFO log for
stateful session terminations, and switch the stateless path to a DEBUG
log with a clearer message ("Stateless request completed, cleaning up
transport"). Adds two caplog tests covering both branches.

Closes #2329.

Author: adityasingh2400

src/mcp/server/streamable_http.py

@@ -767,7 +767,10 @@ async def terminate(self) -> None:
         """
 
         self._terminated = True
-        logger.info(f"Terminating session: {self.mcp_session_id}")
+        if self.mcp_session_id is not None:
+            logger.info(f"Terminating session: {self.mcp_session_id}")
+        else:
+            logger.debug("Stateless request completed, cleaning up transport")
 
         # We need a copy of the keys to avoid modification during iteration
         request_stream_keys = list(self._request_streams.keys())

tests/shared/test_streamable_http.py

@@ -7,6 +7,7 @@
 from __future__ import annotations as _annotations
 
 import json
+import logging
 import time
 from collections.abc import AsyncIterator
 from contextlib import asynccontextmanager
@@ -588,6 +589,43 @@ def test_streamable_http_transport_init_validation() -> None:
         StreamableHTTPServerTransport(mcp_session_id="test\n")
 
 
+@pytest.mark.anyio
+async def test_terminate_stateless_log_is_debug(caplog: pytest.LogCaptureFixture):
+    """Stateless terminate() should not emit INFO 'Terminating session: None'.
+
+    Regression test for issue #2329: in stateless mode the transport has no
+    session id, so the prior INFO log produced 'Terminating session: None' on
+    every request. The stateless path now logs at DEBUG with a clearer message,
+    while the stateful path keeps the INFO-level log.
+    """
+    transport = StreamableHTTPServerTransport(mcp_session_id=None)
+
+    with caplog.at_level(logging.DEBUG, logger="mcp.server.streamable_http"):
+        await transport.terminate()
+
+    info_records = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not any("Terminating session" in r.getMessage() for r in info_records), (
+        "Stateless terminate() must not emit INFO 'Terminating session: ...'"
+    )
+    assert any(
+        r.levelno == logging.DEBUG and "Stateless request completed" in r.getMessage() for r in caplog.records
+    ), "Stateless terminate() should log a DEBUG completion message"
+
+
+@pytest.mark.anyio
+async def test_terminate_stateful_log_is_info(caplog: pytest.LogCaptureFixture):
+    """Stateful terminate() should still log session id at INFO (#2329)."""
+    session_id = "abc123"
+    transport = StreamableHTTPServerTransport(mcp_session_id=session_id)
+
+    with caplog.at_level(logging.INFO, logger="mcp.server.streamable_http"):
+        await transport.terminate()
+
+    assert any(
+        r.levelno == logging.INFO and f"Terminating session: {session_id}" in r.getMessage() for r in caplog.records
+    ), "Stateful terminate() must still emit INFO 'Terminating session: <id>'"
+
+
 @pytest.mark.anyio
 async def test_session_termination(basic_app: Starlette) -> None:
     """DELETE terminates the session, after which requests for it return 404."""