protected function visit_headers(RequestInterface $request, $value, $flags)
{
if (!is_array($value)) {
throw new InvalidArgumentException('headers value must be an array');
}
if ($flags & self::OPTIONS_AS_DEFAULTS) {
// Merge headers in but do not overwrite existing values
foreach ($value as $key => $header) {
if (!$request->hasHeader($key)) {
$request->setHeader($key, $header);
}
}
} else {
$request->addHeaders($value);
}
}
