yii\httpclient\Message::composeHeaderLines PHP Method

    public function composeHeaderLines()
    {
        if (!$this->hasHeaders()) {
            return [];
        }
        $headers = [];
        foreach ($this->getHeaders() as $name => $values) {
            $name = str_replace(' ', '-', ucwords(str_replace('-', ' ', $name)));
            foreach ($values as $value) {
                $headers[] = "{$name}: {$value}";
            }
        }
        return $headers;
    }

 /**
  * @inheritdoc
  */
 public function composeHeaderLines()
 {
     $headers = parent::composeHeaderLines();
     if ($this->hasCookies()) {
         $headers[] = $this->composeCookieHeader();
     }
     return $headers;
 }