Arnold Wender
b226251ddf
* fix(mcp): redirect stdout to stderr during import to protect JSON-RPC channel (#225) Fixes #225. Several transitive dependencies (chromadb, onnxruntime, posthog) print banners and warnings to stdout — sometimes at the C level — during the mcp_server import chain. Because the MCP protocol multiplexes JSON-RPC over stdio, any non-JSON output on stdout corrupted the message stream and broke Claude Desktop's parser with errors like: MCP mempalace: Unexpected token '*', "**********"... is not valid JSON MCP mempalace: Unexpected token 'E', "EP Error D"... is not valid JSON MCP mempalace: Unexpected token 'F', "Falling ba"... is not valid JSON Reproduced on Windows 11 with mempalace 3.0.0 / Python 3.10 / Claude Desktop 1.1062.0. Fix: at module load, redirect stdout to stderr at both the Python level (sys.stdout = sys.stderr) and the file-descriptor level (os.dup2(2, 1)) to catch C-level prints, while preserving the real stdout for later restore. main() calls _restore_stdout() right before entering the protocol loop so JSON-RPC responses still go to the real stdout. Adds tests/test_mcp_stdio_protection.py with three regression tests: - module-level redirect is in place after import - _restore_stdout() restores the original stdout (idempotent) - 'python -m mempalace.mcp_server' with empty stdin emits no stdout * style: reformat with ruff 0.4 (CI version) for #225
84 lines
2.9 KiB
Python
84 lines
2.9 KiB
Python
"""Regression tests for issue #225 — MCP stdio protection.
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The MCP protocol multiplexes JSON-RPC over stdio. Stdout MUST carry only
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valid JSON-RPC messages. Several transitive deps (chromadb → onnxruntime,
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posthog telemetry) print banners and warnings to stdout — sometimes at
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the C level — which broke Claude Desktop's JSON parser on Windows.
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The fix in mcp_server.py redirects stdout → stderr at both the Python
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and file-descriptor level during module import, then restores the real
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stdout in main() before entering the protocol loop.
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"""
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import subprocess
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import sys
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import textwrap
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def test_module_import_redirects_stdout_to_stderr():
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"""At import time, sys.stdout must point at sys.stderr so any stray
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print() from a transitive dependency is sent to stderr."""
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code = textwrap.dedent(
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"""
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import sys
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original_stdout = sys.stdout
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from mempalace import mcp_server
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assert sys.stdout is sys.stderr, (
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f"Expected sys.stdout to be redirected to sys.stderr, "
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f"got: {sys.stdout!r}"
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)
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assert mcp_server._REAL_STDOUT is original_stdout, (
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"mcp_server._REAL_STDOUT must hold the original stdout"
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)
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print("OK", file=sys.stderr)
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"""
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)
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result = subprocess.run(
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[sys.executable, "-c", code],
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capture_output=True,
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timeout=60,
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)
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assert result.returncode == 0, f"stdout: {result.stdout!r}\nstderr: {result.stderr!r}"
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def test_restore_stdout_returns_real_stdout():
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"""_restore_stdout() must reassign sys.stdout to the original handle
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so main() can write JSON-RPC responses to the real stdout."""
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code = textwrap.dedent(
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"""
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import sys
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original_stdout = sys.stdout
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from mempalace import mcp_server
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assert sys.stdout is sys.stderr
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mcp_server._restore_stdout()
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assert sys.stdout is original_stdout, (
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f"After _restore_stdout(), sys.stdout must be the original; "
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f"got: {sys.stdout!r}"
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)
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mcp_server._restore_stdout() # idempotent
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print("OK", file=sys.stderr)
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"""
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)
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result = subprocess.run(
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[sys.executable, "-c", code],
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capture_output=True,
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timeout=60,
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)
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assert result.returncode == 0, f"stdout: {result.stdout!r}\nstderr: {result.stderr!r}"
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def test_mcp_server_no_stdout_noise_on_clean_exit():
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"""`python -m mempalace.mcp_server` with empty stdin must produce
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nothing on stdout. Empty input → readline() returns '' → main()
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breaks out cleanly. Any stdout content here would corrupt the
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JSON-RPC stream in real use."""
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proc = subprocess.run(
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[sys.executable, "-m", "mempalace.mcp_server"],
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input=b"",
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capture_output=True,
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timeout=60,
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)
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assert (
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proc.stdout == b""
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), f"stdout must be empty before the first JSON-RPC response, but got: {proc.stdout!r}"
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