code: protected function getAllHeaders()
      {
          if (function_exists('getallheaders')) {
              return getallheaders();
          }
  
          // 对没有getallheaders函数做处理
          $headers = [];
          foreach ($_SERVER as $name => $value) {
              if (is_array($value) || substr($name, 0, 5) != 'HTTP_') {
                  continue;
              }
  
              $headerKey = implode('-', array_map('ucwords', explode('_', strtolower(substr($name, 5)))));
              $headers[$headerKey] = $value;
          }
  
          return $headers;
      }
docs: 初始化请求Header头信息
  
  @return array|false