gistfile1

<?php
namespace Custom\View\Strategy;

use Zend\EventManager\EventCollection,
    Zend\EventManager\ListenerAggregate,
    Zend\Http\Request as HttpRequest,
    Zend\Http\Response as HttpResponse,
    Zend\View\Model,
    Zend\View\Renderer\JsonRenderer,
    Zend\View\ViewEvent;

class JsonStrategy implements ListenerAggregate
{
    protected $listeners = array();

    protected $renderer;

    public function __construct(JsonRenderer $renderer)
    {
        $this->renderer = $renderer;
    }

    public function attach(EventCollection $events, $priority = 1)
    {
        $this->listeners[] = $events->attach('renderer', array($this, 'selectRenderer'), $priority);
        $this->listeners[] = $events->attach('response', array($this, 'injectResponse'), $priority);
    }

    public function detach(EventCollection $events)
    {
        foreach ($this->listeners as $index => $listener) {
            if ($events->detach($listener)) {
                unset($this->listeners[$index]);
            }
        }
    }

    public function selectRenderer(ViewEvent $e)
    {
        // We assume if attached, this is the selected renderer.
        // So, let's manipulate the view model'
        $model   = $e->getViewModel();
        $data    = $model->getVariables();
        $request = $e->getRequest();

        // Create a new payload and use this as the view model
        $payload = array(
            'error'      => /* logic for returning this */,
            'isRedirect' => $request->isRedirect(),
            'data'       => $data,
        );
        $model = new JsonModel($payload);
        $e->setViewModel($model);

        // Now we can return the renderer
        return $this->renderer;
    }

    public function injectResponse(ViewEvent $e)
    {
        $renderer = $e->getRenderer();
        if ($renderer !== $this->renderer) {
            // Discovered renderer is not ours; do nothing
            return;
        }

        $result   = $e->getResult();
        if (!is_string($result)) {
            // We don't have a string, and thus, no JSON
            return;
        }

        // Populate response
        $response = $e->getResponse();
        $response->setContent($result);
        $headers = $response->headers();
        $headers->addHeaderLine('content-type', 'application/json');
    }
}