Decompressing archives with boost and filtering streams

I am working on decompressing large files, with contains specified blocks of compressed data various ways. I wrote a following code:

// input_file - path to file
std::ifstream file(input_file, std::ios_base::in | std::ios_base::binary);
//move to begin of n-th data block, compressed by zlib
file.seekg(offset, std::ios_base::beg);
boost::iostreams::filtering_streambuf<boost::iostreams::input> in;
in.push(boost::iostreams::zlib_decompressor());
in.push(file);
// write decompressed data to output file
boost::iostreams::copy(in, output);

My understanding is this line

boost::iostreams::copy(in, output); 

will start decompressing and copying data until the end of the file, which is unwanted in that case.

It is important that, know the proper offset and length of compressed data.

Boost documentation says that:

A model of Source can be defined as follows:

struct Source {
    typedef char        char_type;
    typedef source_tag  category;
    std::streamsize read(char* s, std::streamsize n) 
    {
        // Read up to n characters from the input 
        // sequence into the buffer s, returning   
        // the number of characters read, or -1 
        // to indicate end-of-sequence.
    }
};

I wanted to inherit from ifstream class, overwrite it read method, and inside that method calculate how many bytes were read and return -1 if there is no more data in that chunk, but unfortunately, it seems not working.

I wrote:

class ifstream_t : public std::ifstream{
     public:
     ifstream_t(const std::string& fp, std::ios_base::openmode mode = std::ios_base::in) : std::ifstream(fp, mode){}
     std::streamsize read(char* s, std::streamsize n) {
         // calculate remaining bytes 
         return -1;
     }   
};

and used it in:

ifstream_t file(this->fp, std::ios_base::in | std::ios_base::binary);
boost::iostreams::filtering_streambuf<boost::iostreams::input> in;
in.push(boost::iostreams::zlib_decompressor());
in.push(file);
boost::iostreams::copy(in, output);

method read, from my class in not invoked.