internal static void EscapeAsciiChar(byte b, ref ValueStringBuilder to)
{
to.Append('%');
HexConverter.ToCharsBuffer(b, to.AppendSpan(2), 0, HexConverter.Casing.Upper);
}
internal static bool IsHexDigit(char character) => HexConverter.IsHexChar(character);
private static void EscapeStringToBuilder(
ReadOnlySpan <char> stringToEscape, ref ValueStringBuilder vsb,
ReadOnlySpan <bool> noEscape, bool checkExistingEscaped)
{
// Allocate enough stack space to hold any Rune's UTF8 encoding.
Span <byte> utf8Bytes = stackalloc byte[4];
// Then enumerate every rune in the input.
SpanRuneEnumerator e = stringToEscape.EnumerateRunes();
while (e.MoveNext())
{
Rune r = e.Current;
if (!r.IsAscii)
{
// The rune is non-ASCII, so encode it as UTF8, and escape each UTF8 byte.
r.TryEncodeToUtf8(utf8Bytes, out int bytesWritten);
foreach (byte b in utf8Bytes.Slice(0, bytesWritten))
{
vsb.Append('%');
HexConverter.ToCharsBuffer(b, vsb.AppendSpan(2), 0, HexConverter.Casing.Upper);
}
continue;
}
// If the value doesn't need to be escaped, append it and continue.
byte value = (byte)r.Value;
if (noEscape[value])
{
vsb.Append((char)value);
continue;
}
// If we're checking for existing escape sequences, then if this is the beginning of
// one, check the next two characters in the sequence. This is a little tricky to do
// as we're using an enumerator, but luckily it's a ref struct-based enumerator: we can
// make a copy and iterate through the copy without impacting the original, and then only
// push the original ahead if we find what we're looking for in the copy.
if (checkExistingEscaped && value == '%')
{
// If the next two characters are valid escaped ASCII, then just output them as-is.
SpanRuneEnumerator tmpEnumerator = e;
if (tmpEnumerator.MoveNext())
{
Rune r1 = tmpEnumerator.Current;
if (r1.IsAscii && IsHexDigit((char)r1.Value) && tmpEnumerator.MoveNext())
{
Rune r2 = tmpEnumerator.Current;
if (r2.IsAscii && IsHexDigit((char)r2.Value))
{
vsb.Append('%');
vsb.Append((char)r1.Value);
vsb.Append((char)r2.Value);
e = tmpEnumerator;
continue;
}
}
}
}
// Otherwise, append the escaped character.
vsb.Append('%');
HexConverter.ToCharsBuffer(value, vsb.AppendSpan(2), 0, HexConverter.Casing.Upper);
}
}