在 Flask 中使用 HTML POST 操作刷新变量

Question

I am trying to build a simple numeric captcha for my contact page in Flask. The contact page end-point loads in GET mode and initializes the values of the captcha verification. When I submit the form in POST mode, I expect my user-entered form value to match the captcha value. However, it is not working as expected. I did some troubleshooting with print statements to see how the values are changing and it appears that the captcha variables are getting re-initialised with the POST operation. Can someone please suggest a workaround? My Python code is shared below:

@bp.route('/contact/', methods=('GET', 'POST'))
def contact():
    # Initialize captcha values
    cap_a = random.randint(0, 9)
    cap_b = random.randint(0, 9)
    cap_prod = cap_a * cap_b
    print(cap_a, cap_b, cap_prod)
    if request.method == "POST":
        error = None
        log_file = current_app.config['LOGFILE']
        full_name = request.form['fullname']
        email_addr = request.form['email']
        phone_no = request.form['phone']
        msg_body = request.form['message']
        num_prod = request.form['verifycaptcha']
        print(cap_a, cap_b, cap_prod)
        print(full_name, email_addr, phone_no, msg_body, num_prod)
        if not full_name:
            error = 'Full name is required.'
        elif not email_addr:
            error = 'Email address is required.'
        elif not msg_body:
            error = 'Message body is required.'
        if num_prod != cap_prod:
            error = 'Incorrect captcha verification.'
        if error is None:
            # Perform some operations
            pass
            try:
                with current_app.app_context():
                    mail = Mail()
                    mail.init_app(current_app)
                    mail.send(msg)
                    error = 'Mail sent successfully!'
            except:
                error = 'Mail engine error encountered. Please retry after some time.'
                f = open(log_file, "a")
                f.write('['+datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')+'] '+error+'\n')
                f.close()
        flash(error)
    return render_template('contact.html',num_a = cap_a, num_b = cap_b)

Answer 1

cap_a = random.randint(0, 9)
cap_b = random.randint(0, 9)
cap_prod = cap_a * cap_b

these are 2 random numbers and you are creating cap_prod. You are not saving the cap_prod anywhere. You are instead calculating it again when POST request comes (this time it will be 2 new random numbers)

You need to save the captcha that you created during the GET, and then when the POST comes, compare with the value that was originally sent.

If you are going to support refresh-captcha image in the future (you need to have an API call that will generate a new captcha and save it)

Answer 2

I figured out the solution by storing the captcha variables in the session dictionary of Flask and checking for its existence before re-initialising the values.

def contact():
    # Initialize captcha values
    if 'product' not in session:
        cap_a = random.randint(0, 9)
        cap_b = random.randint(0, 9)
        session['captcha_a'] = cap_a
        session['captcha_b'] = cap_b
        session['product'] = cap_a * cap_b
    else:
        cap_a = session.get('captcha_a')
        cap_b = session.get('captcha_b')
    if request.method == "POST":
        pass
        # Rest of the code

Working examples of the above solution can be found at Fadmeter.com and FadURL.com .