Function gzoffset 

pub unsafe extern "C" fn gzoffset(file: gzFile) -> z_off_t

Available on crate feature gz only.

Return the current compressed (actual) read or write offset of file. This offset includes the count of bytes that precede the gzip stream, for example when appending or when using gzdopen for reading. When reading, the offset does not include as yet unused buffered input. This information can

Returns

• The number of bytes prior to the current read or write position in the compressed data stream, on success.
• -1 on error.

Safety

• file, if non-null, must be an open file handle obtained from gzopen or gzdopen.