new

/*
 * call-seq: Zlib::GzipWriter.new(io, level, strategy)
 *
 * Creates a GzipWriter object associated with +io+. +level+ and +strategy+
 * should be the same as the arguments of Zlib::Deflate.new.  The GzipWriter
 * object writes gzipped data to +io+.  At least, +io+ must respond to the
 * +write+ method that behaves same as write method in IO class.
 */
static VALUE
rb_gzwriter_initialize(argc, argv, obj)
    int argc;
    VALUE *argv;
    VALUE obj;
{
    struct gzfile *gz;
    VALUE io, level, strategy;
    int err;

    rb_scan_args(argc, argv, "12", &io, &level, &strategy);
    Data_Get_Struct(obj, struct gzfile, gz);

    /* this is undocumented feature of zlib */
    gz->level = ARG_LEVEL(level);
    err = deflateInit2(&gz->z.stream, gz->level, Z_DEFLATED,
                       -MAX_WBITS, DEF_MEM_LEVEL, ARG_STRATEGY(strategy));
    if (err != Z_OK) {
        raise_zlib_error(err, gz->z.stream.msg);
    }
    gz->io = io;
    ZSTREAM_READY(&gz->z);

    return obj;
}