Firebase初始化报错：默认应用已存在问题求助

问题详情 #

代码中每次处理接口请求时都会初始化Firebase应用，导致触发以下错误：

ERROR The default Firebase app already exists. This means you called initialize_app() more than once without providing an app name as the second argument. In most cases you only need to call initialize_app() once. But if you do want to initialize multiple apps, pass a second argument to initialize_app() to give each app a unique name.

涉及代码：

@event_routes.route('/scanner/events', methods=['GET'], cors=True)
def get_scanner_events() -> Response:
    
    try:
        id_token = event_routes.current_request.headers["IdToken"]
    except KeyError:
        return Response(body={"message": "missing id token for authentication"}, status_code=400,
                        headers={"Content-Type": "application/json"})


  
   # add json content (dict) 
    try:
        GOOGLE_APPLICATION_CREDENTIALS = json.loads(os.getenv("GOOGLE_APPLICATION_CREDENTIALS", ""))
        TEST_GOOGLE_PRIVATE_KEY = os.getenv("TEST_GOOGLE_PRIVATE_KEY", "").replace(r'\n', '\n')
        GOOGLE_APPLICATION_CREDENTIALS['private_key'] = TEST_GOOGLE_PRIVATE_KEY 

        cred = firebase_admin.credentials.Certificate(GOOGLE_APPLICATION_CREDENTIALS)
        firebase_app = firebase_admin.initialize_app(credential=cred)
        value = firebase_admin.auth.verify_id_token(id_token) 
        # print("made it here")
        print(firebase_app.project_id)
        
    except auth.InvalidIdTokenError as e:
        print("InvalidIdTokenError")
        return Response(body={"message": "invalid id token"}, status_code=400,
                        headers={"Content-Type": "application/json"})

解决方案 #

核心原因 #

Firebase默认应用只能初始化一次，你的代码在每次接口请求时都会调用initialize_app()，重复执行就会触发该错误。

修复方案1：启动时一次性初始化（推荐） #

把Firebase应用初始化逻辑移到接口函数外部，在服务启动时仅执行一次：

# 放在文件顶部，服务启动时执行
import firebase_admin
from firebase_admin import credentials, auth
import json
import os

# 初始化Firebase应用
GOOGLE_APPLICATION_CREDENTIALS = json.loads(os.getenv("GOOGLE_APPLICATION_CREDENTIALS", ""))
TEST_GOOGLE_PRIVATE_KEY = os.getenv("TEST_GOOGLE_PRIVATE_KEY", "").replace(r'\n', '\n')
GOOGLE_APPLICATION_CREDENTIALS['private_key'] = TEST_GOOGLE_PRIVATE_KEY 

cred = credentials.Certificate(GOOGLE_APPLICATION_CREDENTIALS)
# 检查是否已有初始化的应用，避免重复创建
if not firebase_admin._apps:
    firebase_admin.initialize_app(cred)

# 接口函数保持原有逻辑，移除内部初始化代码
@event_routes.route('/scanner/events', methods=['GET'], cors=True)
def get_scanner_events() -> Response:
    
    try:
        id_token = event_routes.current_request.headers["IdToken"]
    except KeyError:
        return Response(body={"message": "missing id token for authentication"}, status_code=400,
                        headers={"Content-Type": "application/json"})

    try:
        value = auth.verify_id_token(id_token) 
        # 获取已初始化的默认应用实例
        print(firebase_admin.get_app().project_id)
        
    except auth.InvalidIdTokenError as e:
        print("InvalidIdTokenError")
        return Response(body={"message": "invalid id token"}, status_code=400,
                        headers={"Content-Type": "application/json"})

修复方案2：函数内检查应用是否存在 #

如果必须在接口函数内处理初始化，先判断默认应用是否已创建：

@event_routes.route('/scanner/events', methods=['GET'], cors=True)
def get_scanner_events() -> Response:
    
    try:
        id_token = event_routes.current_request.headers["IdToken"]
    except KeyError:
        return Response(body={"message": "missing id token for authentication"}, status_code=400,
                        headers={"Content-Type": "application/json"})

    try:
        GOOGLE_APPLICATION_CREDENTIALS = json.loads(os.getenv("GOOGLE_APPLICATION_CREDENTIALS", ""))
        TEST_GOOGLE_PRIVATE_KEY = os.getenv("TEST_GOOGLE_PRIVATE_KEY", "").replace(r'\n', '\n')
        GOOGLE_APPLICATION_CREDENTIALS['private_key'] = TEST_GOOGLE_PRIVATE_KEY 

        cred = firebase_admin.credentials.Certificate(GOOGLE_APPLICATION_CREDENTIALS)
        # 检查默认应用是否存在，不存在才初始化
        if not firebase_admin._apps:
            firebase_app = firebase_admin.initialize_app(cred)
        else:
            firebase_app = firebase_admin.get_app()
        
        value = firebase_admin.auth.verify_id_token(id_token) 
        print(firebase_app.project_id)
        
    except auth.InvalidIdTokenError as e:
        print("InvalidIdTokenError")
        return Response(body={"message": "invalid id token"}, status_code=400,
                        headers={"Content-Type": "application/json"})

关键说明 #

• 方案1性能更优，因为初始化是耗时操作，无需每次请求重复执行。
• firebase_admin._apps是Firebase内部存储所有应用实例的集合，通过它可以快速判断是否已有初始化的应用。
• 只有在需要同时连接多个Firebase项目时，才需要给initialize_app()传入唯一名称作为第二个参数（如initialize_app(cred, name="secondary-app")），常规场景使用默认应用即可。

内容的提问来源于stack exchange，提问作者guiguilecodeur