Files
superset2/superset/mcp_service/flask_singleton.py
2026-01-21 11:10:31 -08:00

125 lines
4.8 KiB
Python

# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements. See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership. The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied. See the License for the
# specific language governing permissions and limitations
# under the License.
"""
Simple module-level Flask app instance for MCP service.
Following the Stack Overflow recommendation:
"a simple module with just the instance is enough"
- The module itself acts as the singleton
- No need for complex patterns or metaclasses
- Clean and Pythonic approach
"""
import logging
import os
from flask import current_app, Flask, has_app_context
logger = logging.getLogger(__name__)
logger.info("Creating Flask app instance for MCP service")
try:
from superset.extensions import appbuilder
# Check if appbuilder is already initialized (main Superset app is running).
# If so, reuse that app to avoid corrupting the shared appbuilder singleton.
# Calling create_app() again would re-initialize appbuilder and break views.
#
# NOTE: appbuilder.app now returns a LocalProxy to current_app (Flask-AppBuilder
# deprecation), so we can't use `appbuilder.app is not None` as that always
# returns True (compares LocalProxy object, not the resolved value).
# Instead, check if init_app was called by looking at _session.
appbuilder_initialized = appbuilder._session is not None
if appbuilder_initialized and has_app_context():
# We're in an app context (e.g., during main Superset startup),
# so we can get the actual Flask app instance from current_app
logger.info("Reusing existing Flask app from app context for MCP service")
# Use _get_current_object() to get the actual Flask app, not the LocalProxy
app = current_app._get_current_object()
else:
# Either appbuilder is not initialized (standalone MCP server),
# or appbuilder is initialized but we're not in an app context
# (edge case - should rarely happen). In both cases, create a minimal app.
#
# We avoid calling create_app() which would run full FAB initialization
# and could corrupt the shared appbuilder singleton if main app starts.
from superset.app import SupersetApp
from superset.mcp_service.mcp_config import get_mcp_config
if appbuilder_initialized:
logger.warning(
"Appbuilder initialized but not in app context - "
"creating separate MCP Flask app"
)
else:
logger.info("Creating minimal Flask app for standalone MCP service")
# Disable debug mode to avoid side-effects like file watchers
_mcp_app = SupersetApp(__name__)
_mcp_app.debug = False
# Load configuration
config_module = os.environ.get("SUPERSET_CONFIG", "superset.config")
_mcp_app.config.from_object(config_module)
# Apply MCP-specific configuration
mcp_config = get_mcp_config(_mcp_app.config)
_mcp_app.config.update(mcp_config)
# Initialize only the minimal dependencies needed for MCP service
with _mcp_app.app_context():
try:
from superset.extensions import db
db.init_app(_mcp_app)
# Initialize only MCP-specific dependencies
# MCP tools import directly from superset.daos/models, so we only need
# the MCP decorator injection, not the full superset_core abstraction
from superset.core.mcp.core_mcp_injection import (
initialize_core_mcp_dependencies,
)
initialize_core_mcp_dependencies()
logger.info(
"Minimal MCP dependencies initialized for standalone MCP service"
)
except Exception as e:
logger.warning(
"Failed to initialize dependencies for MCP service: %s", e
)
app = _mcp_app
logger.info("Minimal Flask app instance created successfully for MCP service")
except Exception as e:
logger.error("Failed to create Flask app: %s", e)
raise
def get_flask_app() -> Flask:
"""
Get the Flask app instance.
Returns:
Flask: The module-level Flask app instance
"""
return app