Sending Mail Asynchronously

flaskr_01.py

@app.route('/signup', methods=['GET', 'POST'])                                  
def signup():                                                                   
    error = None                                                                
    if request.method == 'POST':                                                
        email = request.form['email']                                           
        password = request.form['password']                                     
        if not (email or password):                                             
            return signup_error('Email Address and Password are required.')        
        db = get_db()                                                              
        c = db.cursor()                                                            
        c.execute('SELECT * FROM users WHERE email=?;', (email,))                  
        if c.fetchone():                                                           
            return signup_error('Email Addres already has an account.')            
        c.execute('INSERT INTO users (email, password) VALUES (?, ?);',            
                  (email, pbkdf2_sha256.hash(password)))                           
        db.commit()                                                                  
        send_welcome_email(email)                                                  
        flash('Account Created')                                                   
        return redirect(url_for('login'))                                          
    else:                                                                          
        return render_template('signup.html')                                      
                                                                                   
                                                                                   
def send_welcome_email(address):                                                   
    res = requests.post(                                                           
        "https://api.mailgun.net/v3/{}/messages".format(app.config['DOMAIN']),  
        auth=("api", MAILGUN_API_KEY),                                             
        data={"from": "Flaskr <noreply@{}>".format(app.config['DOMAIN']),          
              "to": [address],                                                     
              "subject": "Welcome to Flaskr!",                                     
              "text": "Welcome to Flaskr, your account is now active!"}            
    )                                                                              
    if res.status_code != 200:                                                     
        # Something terrible happened :-(                                          
        raise MailgunError("{}-{}".format(res.status_code, res.reason))            
                                                                                   
                                                                                   
def signup_error(error):                                                           
    return render_template('signup.html', error=error)

flaskr_02.py

def connect_queue():                                                                                  
    if not hasattr(g, 'rabbitmq'):                                                                    
        g.rabbitmq = pika.BlockingConnection(                                                         
            pika.ConnectionParameters(app.config['RABBITMQ_HOST'])                                    
        )                                                                                             
    return g.rabbitmq                                                                                 
                                                                                                      
                                                                                                      
def get_welcome_queue():                                                                              
    if not hasattr(g, 'welcome_queue'):                                                               
        conn = connect_queue()                                                                        
        channel = conn.channel()                                                                      
        channel.queue_declare(queue='welcome_queue', durable=True)                                    
        channel.queue_bind(exchange='amq.direct', queue='welcome_queue')                              
        g.welcome_queue = channel                                                                     
    return g.welcome_queue                                                                            
                                                                                                      
                                                                                                      
@app.teardown_appcontext                                                                              
def close_queue(error)                                                                                
    if hasattr(g, 'rabbitmq'):                                                                        
        g.rabbitmq.close()

flaskr_03.py

@app.route('/signup', methods=['GET', 'POST'])                                  
def signup():                                                                   
    error = None                                                                
    if request.method == 'POST':                                                
        email = request.form['email']                                           
        password = request.form['password']                                     
        if not (email or password):                                             
            return signup_error('Email Address and Password are required.')     
        db = get_db()                                                           
        c = db.cursor()                                                         
        c.execute('SELECT * FROM users WHERE email=?;', (email,))               
        if c.fetchone():                                                        
            return signup_error('Email Addres already has an account.')         
        c.execute('INSERT INTO users (email, password) VALUES (?, ?);',         
                  (email, pbkdf2_sha256.hash(password)))                        
        db.commit()                                                             
        q = get_welcome_queue()                                                 
        q.basic_publish(                                                        
            exchange='amq.direct',                                              
            routing_key='welcome_queue',                                        
            body=email,                                                         
            properties=pika.BasicProperties(                                    
                delivery_mode=_DELIVERY_MODE_PERSISTENT                         
            )                                                                   
        )                                                                       
        flash('Account Created')                                                
        return redirect(url_for('login'))                                       
    else:                                                                       
        return render_template('signup.html')

flaskr_04.py

import pika
import requests


# Configuration
DOMAIN = 'example.com'
MAILGUN_API_KEY = 'YOUR_MAILGUN_API_KEY'
RABBITMQ_HOST = 'localhost'

connection = pika.BlockingConnection(
    pika.ConnectionParameters(host=RABBITMQ_HOST)
)
channel = connection.channel()
channel.queue_declare(queue='welcome_queue', durable=True)


class Error(Exception):
    pass


class MailgunError(Error):
    def __init__(self, message):
        self.message = message


def send_welcome_message(ch, method, properties, body):
    address = body.decode('UTF-8')
    print("Sending welcome email to {}".format(address))
    res = requests.post(
        "https://api.mailgun.net/v3/{}/messages".format(DOMAIN),
        auth=("api", MAILGUN_API_KEY),
        data={"from": "Flaskr <noreply@{}>".format(DOMAIN),
              "to": [address],
              "subject": "Welcome to Flaskr!",
              "text": "Welcome to Flaskr, your account is now active!"}
    )
    ch.basic_ack(delivery_tag=method.delivery_tag)
    if res.status_code != 200:
        # Something terrible happened :-O
        raise MailgunError("{}-{}".format(res.status_code, res.reason))


channel.basic_consume(send_welcome_message, queue='welcome_queue')
channel.start_consuming()

flaskr_05.py

retry_channel = connection.channel()
retry_channel.queue_declare(
    queue='retry_queue',
    durable=True,
    arguments={
        'x-message-ttl': RETRY_DELAY_MS,
        'x-dead-letter-exchange': 'amq.direct',
        'x-dead-letter-routing-key': 'welcome_queue'
    }
)


def send_welcome_message(ch, method, properties, body):
    address = body.decode('UTF-8')
    print("Sending welcome email to {}".format(address))
    res = requests.post(
        "https://api.mailgun.net/v3/{}/messages".format(DOMAIN),
        auth=("api", MAILGUN_API_KEY),
        data={"from": "Flaskr <noreply@{}>".format(DOMAIN),
              "to": [address],
              "subject": "Welcome to Flaskr!",
              "text": "Welcome to Flaskr, your account is now active!"}
    )
    ch.basic_ack(delivery_tag=method.delivery_tag)
    if res.status_code != 200:
        print("Error sending to {}. {} {}. Retrying...".format(
            address, res.status_code, res.reason
        ))
        retry_channel.basic_publish(
            exchange='',
            routing_key='retry_queue',
            body=address,
            properties=pika.BasicProperties(
                delivery_mode=_DELIVERY_MODE_PERSISTENT
            )
        )