Question

I am developing a custom field for the Forms Component in Silex. The purpose of this field is to render and validate a captcha image/value.

I was able to add a FormExtension that registers my custom type.
I am injecting the $app['session'] to be able to store the captcha value in the session. Everything seems to work as expected until I start on touching the session.

Here’s the error I get:

Failed to start the session because headers have already been sent.

Hereunder is how I register my FormExtension and how it instanciates the custom field type:

$app->register(new FormServiceProvider());
$app['form.extensions'] = $app->share(
    $app->extend('form.extensions', function ($extensions) use ($app) {
        $extensions[] = new CaptchaFormExtension($app['captcha.options'], $app['session']);
        return $extensions;
    })
);

class CaptchaFormExtension extends AbstractExtension
{
    private $session;
    private $options;

    public function __construct($options = array(), Session $session)
    {
        $this->options = $options;
        $this->session = $session;
    }

    protected function loadTypes()
    {
        return array(
            new CaptchaType($this->options, $this->session)
        );
    }
}

Answer 1

So I have figured out what the problem was.
The error message was actually pretty much self-explanatory.

Actually I don’t use the session prior to the calls in the CaptchaType so it only gets started at that point, which is, as the error message says, too late.

Solution I have came up with is to explicitly start the session at the beginning of my controller action. I can then use the session inside the custom form type as I want to.

$app->get('/contact', function() use ($app) {

    $app['session']->start();

    $form = $app['form.factory']->create(new ContactFormType(), new ContactMessage());

    ...

});