private Regex /*!*/ Transform(ref RubyEncoding encoding, MutableString /*!*/ input, int start, out string strInput)
{
ContractUtils.RequiresNotNull(input, "input");
// K-coding of the current operation (the current KCODE gets preference over the KCODE regex option):
RubyRegexOptions kc = _options & RubyRegexOptions.EncodingMask;
if (kc != 0)
{
encoding = _pattern.Encoding;
}
else
{
kc = RubyEncoding.ToRegexOption(encoding);
}
// Convert input to a string. Force k-coding if necessary.
if (kc != 0)
{
// Handling multi-byte K-coded characters is not entirely correct here.
// Three cases to be considered:
// 1) Multi-byte character is explicitly contained in the pattern: /�*/
// 2) Subsequent escapes form a complete character: /\342\202\254*/ or /\xe2\x82\xac*/
// 3) Subsequent escapes form an incomplete character: /[\x7f-\xff]{1,3}/
//
// In the first two cases we want to "group" the byte triplet so that regex operators like *, +, ? and {n,m} operate on
// the entire character, not just the last byte. We could unescape the bytes and replace them with complete Unicode characters.
// Then we could encode the input using the same K-coding and we would get a match.
// However, case 3) requires the opposite: to match the bytes we need to encode the input using binary encoding.
// Using this encoding makes *+? operators operate on the last byte (encoded as UTF16 character).
//
// The right solution would require the regex engine to handle multi-byte escaped characters, which it doesn't.
//
// TODO:
// A correct workaround would be to wrap the byte sequence that forms a character into a non-capturing group,
// for example transform /\342\202\254*/ to /(?:\342\202\254)*/ and use binary encoding on both input and pattern.
// For now, we just detect if there are any non-ascii character escapes. If so we use a binary encoding accomodating case 3),
// but breaking cases 1 and 2. Otherwise we encode using k-coding to make case 1 match.
if (HasEscapedNonAsciiBytes(_pattern))
{
encoding = RubyEncoding.Binary;
kc = 0;
}
strInput = ForceEncoding(input, encoding.Encoding, start);
}
else if (input.Encoding.IsKCoding)
{
strInput = input.ToString(BinaryEncoding.Instance);
}
else
{
_pattern.RequireCompatibleEncoding(input);
input.PrepareForCharacterRead();
strInput = input.ConvertToString();
}
return(TransformPattern(encoding, kc));
}
