var stream = new System.IO.MemoryStream();
var writer = new System.IO.BinaryWriter(stream);

int fileType = 9 | 1 << 25;
int dcId = 2;
long id_ = long.Parse(id);
long access_hash_ = long.Parse(access_hash);

writer.Write(fileType);
writer.Write(dcId);

var b = Encoding.UTF8.GetBytes(file_reference_base64);
if (b.Length <= 253)
{
    writer.Write((byte)b.Length);
}
else
{
    writer.Write((byte)254);
    writer.Write((byte)b.Length);
    writer.Write((byte)(b.Length >> 8));
    writer.Write((byte)(b.Length >> 16));
}

writer.Write(b);

int j = b.Length <= 253 ? 1 : 4;
while ((b.Length + j) % 4 != 0)
{
    writer.Write((byte)0);
    j++;
}

writer.Write(id_);
writer.Write(access_hash_);

writer.Write((byte)30);
writer.Write((byte)4);
writer.Flush();

stream.Seek(0, System.IO.SeekOrigin.Begin);

var bytes = stream.ToArray();
var result = new List<byte>();

for (int n = bytes.Length, i = 0; i < n; i++)
{
    result.Add(bytes[i]);
    if (bytes[i] == 0)
    {
        byte cnt = 1;
        while (cnt < 250 && i + cnt < n && bytes[i + cnt] == bytes[i])
        {
            cnt++;
        }
        result.Add(cnt);
        i += cnt - 1;
    }
}