Allow to fix validation for parameters with a format

src/Handler/ValidatedDescriptionHandler.php

@@ -42,6 +42,11 @@ public function __invoke(callable $handler)
 
             foreach ($operation->getParams() as $name => $schema) {
                 $value = $command[$name];
+
+                if ($value) {
+                    $value = $schema->filter($value);
+                }
+
                 if (! $this->validator->validate($schema, $value)) {
                     $errors = array_merge($errors, $this->validator->getErrors());
                 } elseif ($value !== $command[$name]) {

src/SchemaFormatter.php

@@ -53,7 +53,7 @@ protected function dateFormatter($dateTime, $format)
             $dateTime = new \DateTime($dateTime);
         }
 
-        if ($dateTime instanceof \DateTime) {
+        if ($dateTime instanceof \DateTimeInterface) {
             static $utc;
             if (!$utc) {
                 $utc = new \DateTimeZone('UTC');

tests/Handler/ValidatedDescriptionHandlerTest.php

@@ -86,4 +86,27 @@ public function testValidatesAdditionalParameters()
         $client = new GuzzleClient(new HttpClient(), $description);
         $client->foo(['bar' => new \stdClass()]);
     }
+
+    public function testFilterBeforeValidate()
+    {
+        $description = new Description([
+            'operations' => [
+                'foo' => [
+                    'uri' => 'http://httpbin.org',
+                    'httpMethod' => 'GET',
+                    'parameters' => [
+                        'bar' => [
+                            'location' => 'uri',
+                            'type'     => 'string',
+                            'format'   => 'date-time',
+                            'required' => true
+                        ]
+                    ]
+                ]
+            ]
+        ]);
+
+        $client = new GuzzleClient(new HttpClient(), $description);
+        $client->foo(['bar' => new \DateTimeImmutable()]); // Should not throw any exception
+    }
 }