Created new action to track visits, which returns an empty pixel

module/Core/src/Action/AbstractTrackingAction.php

@@ -0,0 +1,74 @@
+<?php
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Core\Action;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+use Shlinkio\Shlink\Core\Action\Util\ErrorResponseBuilderTrait;
+use Shlinkio\Shlink\Core\Exception\EntityDoesNotExistException;
+use Shlinkio\Shlink\Core\Exception\InvalidShortCodeException;
+use Shlinkio\Shlink\Core\Options\AppOptions;
+use Shlinkio\Shlink\Core\Service\UrlShortenerInterface;
+use Shlinkio\Shlink\Core\Service\VisitsTrackerInterface;
+
+abstract class AbstractTrackingAction implements MiddlewareInterface
+{
+    use ErrorResponseBuilderTrait;
+
+    /**
+     * @var UrlShortenerInterface
+     */
+    private $urlShortener;
+    /**
+     * @var VisitsTrackerInterface
+     */
+    private $visitTracker;
+    /**
+     * @var AppOptions
+     */
+    private $appOptions;
+
+    public function __construct(
+        UrlShortenerInterface $urlShortener,
+        VisitsTrackerInterface $visitTracker,
+        AppOptions $appOptions
+    ) {
+        $this->urlShortener = $urlShortener;
+        $this->visitTracker = $visitTracker;
+        $this->appOptions = $appOptions;
+    }
+
+    /**
+     * Process an incoming server request and return a response, optionally delegating
+     * to the next middleware component to create the response.
+     *
+     * @param ServerRequestInterface $request
+     * @param RequestHandlerInterface $handler
+     *
+     * @return ResponseInterface
+     */
+    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
+    {
+        $shortCode = $request->getAttribute('shortCode', '');
+        $query = $request->getQueryParams();
+        $disableTrackParam = $this->appOptions->getDisableTrackParam();
+
+        try {
+            $longUrl = $this->urlShortener->shortCodeToUrl($shortCode);
+
+            // Track visit to this short code
+            if ($disableTrackParam === null || ! \array_key_exists($disableTrackParam, $query)) {
+                $this->visitTracker->track($shortCode, $request);
+            }
+
+            return $this->createResp($longUrl);
+        } catch (InvalidShortCodeException | EntityDoesNotExistException $e) {
+            return $this->buildErrorResponse($request, $handler);
+        }
+    }
+
+    abstract protected function createResp(string $longUrl): ResponseInterface;
+}