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test: cover raw invalid UTF-8 stdio regression #2370

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test: cover raw invalid UTF-8 stdio regression #2370

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56 changes: 56 additions & 0 deletions tests/issues/test_2328_raw_invalid_utf8_stdio.py
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"""Regression test for issue #2328 - raw invalid UTF-8 over stdio."""

import io
from io import TextIOWrapper

import anyio
import pytest
from pydantic import AnyHttpUrl, TypeAdapter

from mcp.server.mcpserver import MCPServer
from mcp.server.stdio import stdio_server
from mcp.types import JSONRPCResponse, jsonrpc_message_adapter


@pytest.mark.anyio
async def test_raw_invalid_utf8_stdio_request_does_not_crash_server() -> None:
mcp = MCPServer("test")

@mcp.tool()
async def fetch(url: str) -> str:
# Delay validation so stdin can reach EOF and close the session write
# stream before the tool returns its validation failure.
await anyio.sleep(0.1)
return str(TypeAdapter(AnyHttpUrl).validate_python(url))

initialize = (
b'{"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": '
b'{"protocolVersion": "2024-11-05", "capabilities": {}, "clientInfo": '
b'{"name": "test", "version": "1.0"}}}\n'
)
initialized = b'{"jsonrpc": "2.0", "method": "notifications/initialized"}\n'
malformed_call = (
b'{"jsonrpc": "2.0", "id": 3, "method": "tools/call", "params": '
b'{"name": "fetch", "arguments": {"url": "http://x\xff\xfe"}}}\n'
)
raw_stdin = io.BytesIO(initialize + initialized + malformed_call)
stdout = io.StringIO()

async with stdio_server(
stdin=anyio.AsyncFile(TextIOWrapper(raw_stdin, encoding="utf-8", errors="replace")),
stdout=anyio.AsyncFile(stdout),
) as (read_stream, write_stream):
with anyio.fail_after(5):
await mcp._lowlevel_server.run(
read_stream,
write_stream,
mcp._lowlevel_server.create_initialization_options(),
)

stdout.seek(0)
output_lines = [line.strip() for line in stdout.readlines() if line.strip()]

assert output_lines
initialize_response = jsonrpc_message_adapter.validate_json(output_lines[0])
assert isinstance(initialize_response, JSONRPCResponse)
assert initialize_response.id == 1
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