/// <summary>
/// Read the percent-encoding and try unescape it.
///
/// The operation first peek at the character the <paramref name="scan"/>
/// iterator points at. If it is % the <paramref name="scan"/> is then
/// moved on to scan the following to characters. If the two following
/// characters are hexadecimal literals they will be unescaped and the
/// value will be returned.
///
/// If the first character is not % the <paramref name="scan"/> iterator
/// will be removed beyond the location of % and -1 will be returned.
///
/// If the following two characters can't be successfully unescaped the
/// <paramref name="scan"/> iterator will be move behind the % and -1
/// will be returned.
/// </summary>
/// <param name="scan">The value to read</param>
/// <param name="end">The end of the sequence</param>
/// <returns>The unescaped byte if success. Otherwise return -1.</returns>
private static int UnescapePercentEncoding(ref MemoryPoolIterator scan, MemoryPoolIterator end)
{
if (scan.Take() != '%')
{
return(-1);
}
var probe = scan;
int value1 = ReadHex(ref probe, end);
if (value1 == -1)
{
return(-1);
}
int value2 = ReadHex(ref probe, end);
if (value2 == -1)
{
return(-1);
}
if (SkipUnescape(value1, value2))
{
return(-1);
}
scan = probe;
return((value1 << 4) + value2);
}
/// <summary>
/// Read the next char and convert it into hexadecimal value.
///
/// The <paramref name="scan"/> iterator will be moved to the next
/// byte no matter no matter whether the operation successes.
/// </summary>
/// <param name="scan">The value to read</param>
/// <param name="end">The end of the sequence</param>
/// <returns>The hexadecimal value if successes, otherwise -1.</returns>
private static int ReadHex(ref MemoryPoolIterator scan, MemoryPoolIterator end)
{
if (CompareIterators(ref scan, ref end))
{
return(-1);
}
var value = scan.Take();
var isHead = (((value >= '0') && (value <= '9')) ||
((value >= 'A') && (value <= 'F')) ||
((value >= 'a') && (value <= 'f')));
if (!isHead)
{
return(-1);
}
if (value <= '9')
{
return(value - '0');
}
else if (value <= 'F')
{
return((value - 'A') + 10);
}
else // a - f
{
return((value - 'a') + 10);
}
}
private static void Copy(MemoryPoolIterator head, MemoryPoolIterator tail, ref MemoryPoolIterator writer)
{
while (!CompareIterators(ref head, ref tail))
{
writer.Put((byte)head.Take());
}
}