py-push-server/app.py

from typing import Dict, Tuple, Union, Optional
from flask import Flask, request, jsonify, Response
from models import db, VAPIDKey, Subscription
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import ec
from pywebpush import webpush, WebPushException

import base64
import json
import os
import threading
import time

app = Flask(__name__)

class WebPushService():
    """
    This class provides services for sending web push notifications.
    """
    
    def __init__(self, app, config_name: str) -> None:
        """
        Initializes the WebPushService with the given application and configuration name.
        
        Args:
        - app: The application instance where the service will be attached.
        - config_name (str): The name of the configuration to be used.
        
        Attributes:
        - app: The application instance.
        - daily_notification_thread (threading.Thread): A thread to send daily notifications.
        """

        # Setting the application instance        
        self.app = app
        self.app.add_url_rule('/web-push/regenerate_vapid', view_func=self.regenerate_vapid, methods=['POST'])

        # Setting the database URI for the application
        db_uri = os.getenv('SQLALCHEMY_DATABASE_URI', 'sqlite:////app/instance/data/webpush.db')
        # This relative path works in docker-compose
        #db_uri = os.getenv('SQLALCHEMY_DATABASE_URI', 'sqlite:///data/webpush.db')
        self.app.config['SQLALCHEMY_DATABASE_URI'] = db_uri

        # Initializing the database with the application
        db.init_app(self.app)

        # Creating a context for the application and initializing services
        with self.app.app_context():
            self._initialize()

        # Creating and starting a thread to send daily notifications
        self.daily_notification_thread = threading.Thread(target=self._send_daily_notifications)
        self.daily_notification_thread.start()


    def _generate_and_save_vapid_keys(self) -> None:
        """
        Generates VAPID (Voluntary Application Server Identification) keys and saves them to the database.

        The method generates a pair of public and private keys using the elliptic curve SECP256R1.
        Both the public and private keys are then serialized and encoded in base64 format.
        The keys are then stored in the database using a VAPIDKey model.

        Notes:
        - In case of any exception during the key generation or database operations, the error is printed to the console.

        Raises:
        - Exceptions raised by the key generation or database operations are caught and printed.
        """        
        try:
            # Generating a private key using the elliptic curve SECP256R1
            private_key = ec.generate_private_key(ec.SECP256R1(), default_backend())

            # Serializing and encoding the public key to base64 format
            public_key_bytes = private_key.public_key().public_bytes(
                encoding=serialization.Encoding.X962,
                format=serialization.PublicFormat.UncompressedPoint
            )
            public_key_base64 = base64.b64encode(public_key_bytes).decode()

            # Serializing and encoding the private key to base64 format
            private_key_bytes = private_key.private_bytes(
                encoding=serialization.Encoding.DER,
                format=serialization.PrivateFormat.PKCS8,
                encryption_algorithm=serialization.NoEncryption()
            )
            private_key_base64 = base64.b64encode(private_key_bytes).decode()

            # Saving the keys to the database
            key = VAPIDKey(public_key=public_key_base64, private_key=private_key_base64)
            db.session.add(key)
            db.session.commit()

        except Exception as e:
            print(f"Error generating VAPID keys: {e}")

            
    def _initialize(self) -> None:
        """
        Initializes the WebPushService by checking for the presence of VAPID keys in the database.

        If no VAPID keys are found in the database, this method triggers the generation and storage
        of new VAPID keys by invoking the `_generate_and_save_vapid_keys` method.

        Notes:
        - VAPID (Voluntary Application Server Identification) keys are essential for sending push notifications 
          to web clients, hence the check and generation if they don't exist.
        """

        # Checking if there are any VAPID keys in the database
        if not VAPIDKey.query.first():
            
            # Generating and saving VAPID keys if none are found
            self._generate_and_save_vapid_keys()


    @staticmethod
    def _send_push_notification(subscription_info: Dict, message: Dict, vapid_key: VAPIDKey) -> bool:
        """
        Sends a push notification using the provided subscription information, message, and VAPID key.

        Args:
        - subscription_info (Dict): The information required to send the push notification to a specific client.
        - message (Dict): The actual message content to be sent as the push notification.
        - vapid_key (VAPIDKey): The VAPID key model instance containing the private key used for sending the notification.

        Returns:
        - bool: True if the push notification was sent successfully, False otherwise.

        Notes:
        - The `webpush` function is used to send the notification.
        - In case of any exception, especially a WebPushException, the error is printed to the console.
        """

        # Sending the push notification using the webpush function
        try:
            webpush(
                subscription_info=subscription_info,
                data=json.dumps(message),
                vapid_private_key=vapid_key.private_key,
                vapid_claims={"sub": "mailto:matthew.raymer@gmail.com"}
            )
            return True
        
        except WebPushException as ex:
            print(f"Failed to send push notification: {ex}")
            return False


    def _send_daily_notifications(self) -> None:
        """
        Continuously sends daily push notifications to all subscribed clients.

        This method:
        1. Retrieves all subscription data from the database.
        2. Constructs the push notification message.
        3. Sends a push notification to each subscribed client.
        4. Sleeps for 24 hours before repeating the process.

        Notes:
        - The method runs in an infinite loop, meaning it will keep sending notifications until the program is terminated.
        - The notifications are sent using the `_send_push_notification` method.
        - A context for the application is created to enable database operations.
        - The message content for the daily update is hardcoded in this method.
        """
    
        while True:
            
            # Creating a context for the application to enable database operations
            with self.app.app_context():
                
                # Retrieving all subscription data from the database
                all_subscriptions = Subscription.query.all()

                # Retrieving the VAPID key from the database
                vapid_key = VAPIDKey.query.first()

                # Constructing the push notification message
                message = {"title": "Daily Update", "message": "Here's your daily update!"}

                # Sending a push notification to each subscribed client
                for subscription in all_subscriptions:
                    subscription_info = {
                        "endpoint": subscription.endpoint,
                        "keys": {
                            "p256dh": subscription.p256dh,
                            "auth": subscription.auth
                        }
                    }
                    WebPushService._send_push_notification(subscription_info, message, vapid_key)

            # Sleeping for 24 hours before sending the next set of notifications
            time.sleep(24 * 60 * 60)


    def regenerate_vapid(self) -> Tuple[str, int]:
        """
        Endpoint to regenerate VAPID keys.

        This method:
        1. Deletes the current VAPID keys from the database.
        2. Generates and stores new VAPID keys using the `_generate_and_save_vapid_keys` method.

        URL: /web-push/regenerate_vapid
        Method: POST

        Returns:
        - Tuple[str, int]: A JSON response indicating the success or failure of the operation, along with the appropriate HTTP status code.

        Notes:
        - If the operation is successful, a JSON response with a success message is returned with a 200 status code.
        - If there's an error during the operation, a JSON response with the error message is returned with a 500 status code.
        """
        
        # Creating a context for the application to enable database operations
        try:
            with self.app.app_context():
                # Deleting the current VAPID keys from the database
                VAPIDKey.query.delete()
                db.session.commit()

                # Generating and saving new VAPID keys
                self._generate_and_save_vapid_keys()
                
            return jsonify(success=True, message="VAPID keys regenerated successfully"), 200
        
        except Exception as e:
            return jsonify(error=f'Error regenerating VAPID keys: {str(e)}'), 500


    @staticmethod
    @app.route('/web-push/vapid')
    def vapid() -> Response:
        """
        Endpoint to retrieve the current VAPID public key.

        This method fetches the VAPID public key from the database and returns it in a JSON response.

        URL: /web-push/vapid
        Method: GET

        Returns:
        - Response: A JSON response containing the VAPID public key.

        Notes:
        - The response contains a key "vapidKey" with the associated public key as its value.
        """

        # Retrieving the VAPID key from the database
        key = VAPIDKey.query.first()
        
        # Returning the public key in a JSON response
        return jsonify(vapidKey=key.public_key)


    @staticmethod
    @app.route('/web-push/subscribe', methods=['POST'])
    def subscribe() -> Tuple[str, int]:
        """
        Endpoint to handle new web push subscription requests.

        This method:
        1. Retrieves the VAPID key from the database.
        2. Reads the subscription content from the incoming request.
        3. Saves the subscription data to the database.
        4. Sends a confirmation push notification to the new subscriber.

        URL: /web-push/subscribe
        Method: POST

        Returns:
        - Tuple[str, int]: A JSON response indicating the success or failure of the operation, along with the appropriate HTTP status code.

        Notes:
        - If the operation is successful, a confirmation push notification is sent to the subscriber with a success message.
        - If there are no VAPID keys available, an error message is returned with a 500 status code.
        - There's a hardcoded 5-second sleep after saving the subscription, which might be intended for some delay before sending the confirmation. Ensure this is the desired behavior.
        """

        # Retrieving the content from the incoming request
        content = request.json

        # Retrieving the VAPID key from the database
        vapid_key = VAPIDKey.query.first()

        # Checking if the VAPID key is available
        if not vapid_key:
            return jsonify(success=False, error="No VAPID keys available"), 500

        # Creating a new Subscription instance with the provided data
        subscription = Subscription(endpoint=content['endpoint'],
                                    p256dh=content['keys']['p256dh'],
                                    auth=content['keys']['auth'],
                                    vapid_key_id=vapid_key.id)

        # Saving the subscription data to the database
        db.session.add(subscription)
        db.session.commit()

        # Introducing a delay (ensure that gateway endpoint is available)
        time.sleep(10)

        # Constructing the subscription information for the push notification
        subscription_info = {
            "endpoint": subscription.endpoint,
            "keys": {
                "p256dh": subscription.p256dh,
                "auth": subscription.auth
            }
        }

        # Creating a confirmation message for the push notification
        message = {"title": "Subscription Successful", "message": "Thank you for subscribing!"}
        
        # Sending the confirmation push notification
        success = WebPushService._send_push_notification(subscription_info, message, vapid_key)

        # Returning the operation status
        return jsonify(success=success)

    
    @staticmethod
    @app.route('/web-push/unsubscribe', methods=['POST'])
    def unsubscribe() -> Tuple[str, int]:
        """
        Endpoint to handle web push unsubscription requests.

        This method:
        1. Reads the endpoint from the incoming request.
        2. Searches for the subscription in the database using the endpoint.
        3. If found, deletes the subscription from the database.

        URL: /web-push/unsubscribe
        Method: POST

        Returns:
        - Tuple[str, int]: A JSON response indicating the success or failure of the operation, along with the appropriate HTTP status code.

        Notes:
        - If the unsubscription is successful, a JSON response with a success message is returned.
        - If the subscription is not found in the database, an error message is returned with a 404 status code.
        """

        # Retrieving the endpoint from the incoming request        
        content = request.json
        endpoint = content['endpoint']

        # Searching for the subscription in the database using the endpoint        
        subscription = Subscription.query.filter_by(endpoint=endpoint).first()

        # If the subscription is found, delete it from the database
        if subscription:
            db.session.delete(subscription)
            db.session.commit()
            return jsonify(success=True, message="Subscription deleted successfully")
        
        # If the subscription is not found, return an error message
        else:
            return jsonify(success=False, error="Subscription not found"), 404


web_push_service = WebPushService(app, "app")