zip_source_tell —
report current read offset in zip source
#include <zip.h>
zip_int64_t
  
  zip_source_tell(zip_source_t
    *source);
The function zip_source_tell() returns the current read
  offset for source. The return value can be passed to
  zip_source_seek(3) with
  whence set to SEEK_SET to return
  to the same location in the source.
Upon successful completion the current read offset is returned. Otherwise, -1 is
  returned and the error information in source is set to
  indicate the error.
zip_source_tell() was added in libzip 1.0.