zlib and fopen and stream_filter_append, prebuffer read errors help

Hello, I'm trying to read some zlib-compressed data from a regular binary file. When I try to attach the zlib compression filter, I am getting an error: something about how the prebuffered data didn't work with the filter and so the filter wasn't added to the filter chain. I looked and found a way to turn off buffering for stream *writes*, but not for stream reads. Can anyone help with ideas for why this isn't working? I posted questions to comp.lang.php and received no response. Thanks Bob