pass through buffer

Hi, I found some old emails about a pass through stream buffer, but I can't find it in the boost library. Am I going blind? Basically I'm in the middle of writing a gzstream class that compresses and decompresses data to and from a iostream and I thought this pass through buffer would be exactly what I need. Anyone know where it is or have any other pointers for me? Thanks in advance. Cheers, Tom Howard