TextReaderWithNewlines

using System.IO;
using System.Text;

class TextReaderWithNewlines : TextReader
{
    public TextReaderWithNewlines(TextReader inner)
    {
        this.tr = inner;
    }

    readonly TextReader tr;
    readonly StringBuilder buffer = new StringBuilder();

    string ReturnAndEmpty()
    {
        var ret = buffer.ToString();
        buffer.Length = 0;
        return ret;
    }

    public override string ReadLine()
    {
        while (true)
        {
            var as_read = tr.Read();

            if (as_read == -1)
            {
                if (buffer.Length == 0)
                    return null;
                return ReturnAndEmpty();
            }
            var ch = (char)as_read;
            if (ch == '\n')
            {
                buffer.Append(ch);
                return ReturnAndEmpty();
            }
            if (ch == '\r')
            {
                if (tr.Peek() == '\n')
                {
                    buffer.Append(ch);
                    buffer.Append('\n');
                    tr.Read();
                    return ReturnAndEmpty();
                }
            }
            buffer.Append(ch);
        }
    }
}