/// <summary>
/// Checks to see if a CultureInfo is included in range of languages specified
/// by this XmlLanguage.
/// </summary>
/// <remarks>
/// In addition to looking for prefix-matches in IetfLanguageTags, the implementation
/// also considers the Parent relationships among CultureInfo's. So, in
/// particular, this routine will report that "zh-hk" is in the range specified by
/// "zh-hant", even though the latter is not a prefix of the former. And because it
/// doesn't restrict itself to traversing CultureInfo.Parent, it will also report that
/// "sr-latn-sp" is in the range covered by "sr-latn". (Note that "sr-latn" does
/// does not have a registered CultureInfo.)
/// </remarks>
internal static bool RangeIncludes(this XmlLanguage language, CultureInfo culture)
{
if (culture == null)
{
throw new ArgumentNullException(nameof(culture));
}
// no need for special cases for InvariantCulture, which has IetfLanguageTag == ""
// Limit how far we'll walk up the hierarchy to avoid security threat.
// We could check for cycles (e.g., culture.Parent.Parent == culture)
// but in in the case of non-malicious code there should be no cycles,
// whereas in malicious code, checking for cycles doesn't mitigate the
// threat; one could always implement Parent such that it always returns
// a new CultureInfo for which Equals always returns false.
for (int i = 0; i < MaxCultureDepth; ++i)
{
// Note that we don't actually insist on a there being CultureInfo corresponding
// to language.
// The use of language.StartsWith() catches, for example,the case
// where this="sr-latn", and culture.IetfLanguageTag=="sr-latn-sp".
// In such a case, culture.Parent.IetfLanguageTag=="sr".
// (There is no registered CultureInfo with IetfLanguageTag=="sr-latn".)
if (language.IsPrefixOf(culture.IetfLanguageTag))
{
return(true);
}
CultureInfo parentCulture = culture.Parent;
if (parentCulture == null ||
parentCulture.Equals(CultureInfo.InvariantCulture) ||
parentCulture == culture)
{
break;
}
culture = parentCulture;
}
return(false);
}