public override Task<int> ReadBlockAsync(char[] buffer, int index, int count)
{
if (buffer == null)
throw new ArgumentNullException(nameof(buffer), SR.ArgumentNull_Buffer);
if (index < 0 || count < 0)
throw new ArgumentOutOfRangeException((index < 0 ? nameof(index) : nameof(count)), SR.ArgumentOutOfRange_NeedNonNegNum);
if (buffer.Length - index < count)
throw new ArgumentException(SR.Argument_InvalidOffLen);
return Task.FromResult(ReadBlock(buffer, index, count));
}