/// <summary>
/// Instantiates an encoder using a custom allow list of characters.
/// </summary>
protected UnicodeEncoderBase(TextEncoderSettings filter, int maxOutputCharsPerInputChar)
{
_maxOutputCharsPerInputChar = maxOutputCharsPerInputChar;
_allowedCharacters = filter.GetAllowedCharacters();
// Forbid characters that are special in HTML.
// Even though this is a common encoder used by everybody (including URL
// and JavaScript strings), it's unfortunately common for developers to
// forget to HTML-encode a string once it has been URL-encoded or
// JavaScript string-escaped, so this offers extra protection.
ForbidCharacter('<');
ForbidCharacter('>');
ForbidCharacter('&');
ForbidCharacter('\''); // can be used to escape attributes
ForbidCharacter('\"'); // can be used to escape attributes
ForbidCharacter('+'); // technically not HTML-specific, but can be used to perform UTF7-based attacks
// Forbid codepoints which aren't mapped to characters or which are otherwise always disallowed
// (includes categories Cc, Cs, Co, Cn, Zs [except U+0020 SPACE], Zl, Zp)
_allowedCharacters.ForbidUndefinedCharacters();
}
public static bool IsCharacterAllowed(this TextEncoderSettings settings, char character)
{
var bitmap = settings.GetAllowedCharacters();
return(bitmap.IsCharacterAllowed(character));
}