fix: improve JSON validation in isJson() and loadJsonAsArray() methods

Author: Grotax

src/FeedIo/Reader/Document.php

@@ -28,13 +28,15 @@ public function startWith(string $character): bool
 
     public function isJson(): bool
     {
-        if (! $this->startWith('{')) {
+        if (! $this->startWith('{') && ! $this->startWith('[')) {
+            return false;
+        }
+        try {
+            json_decode($this->content, false, 512, JSON_THROW_ON_ERROR);
+            return true;
+        } catch (\JsonException $e) {
             return false;
         }
-
-        json_decode($this->content);
-
-        return json_last_error() === JSON_ERROR_NONE;
     }
 
     public function isXml(): bool
@@ -72,7 +74,7 @@ protected function loadDomDocument(): DOMDocument
          * @param string $errno
          */
             function ($errno, $errstr) {
-                throw new \InvalidArgumentException("malformed xml string. parsing error : $errstr ($errno)");
+                throw new \InvalidArgumentException("malformed xml string. parsing error: $errstr ($errno)");
             }
         );
 
@@ -100,6 +102,12 @@ protected function loadJsonAsArray(): array
             );
         }
 
+        if (! is_array($result)) {
+            throw new \InvalidArgumentException(
+                'JSON content must decode to an array or object, got: ' . gettype($result)
+            );
+        }
+
         return $result;
     }
 }