Created middleware which injects default short code length from config when a value was not explicitly provided

module/Rest/src/Middleware/ShortUrl/DefaultShortCodesLengthMiddleware.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Rest\Middleware\ShortUrl;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+use Shlinkio\Shlink\Core\Validation\ShortUrlMetaInputFilter;
+
+class DefaultShortCodesLengthMiddleware implements MiddlewareInterface
+{
+    private int $defaultShortCodesLength;
+
+    public function __construct(int $defaultShortCodesLength)
+    {
+        $this->defaultShortCodesLength = $defaultShortCodesLength;
+    }
+
+    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
+    {
+        $body = $request->getParsedBody();
+        if (! isset($body[ShortUrlMetaInputFilter::SHORT_CODE_LENGTH])) {
+            $body[ShortUrlMetaInputFilter::SHORT_CODE_LENGTH] = $this->defaultShortCodesLength;
+        }
+
+        return $handler->handle($request->withParsedBody($body));
+    }
+}