void readHeader()
{
byte[] header = new byte[this.headersize];
this.fromfile.Seek(this.seekStart, System.IO.SeekOrigin.Begin);
this.fromfile.Read(header, 0, this.headersize);
int index = 0;
// check prefix
foreach (byte b in HEADERPREFIX)
{
if (header[index]!=b)
{
throw new BufferFileException("invalid header prefix");
}
index++;
}
// skip version (for now)
index++;
// read buffersize
this.buffersize = Retrieve(header, index);
this.sanityCheck();
//this.header = header;
}