> In arc.c, it seems, that :
>  in dump_chunk
>    back[p].r.adr (wich contains datas) is defined only for
> text/html type.
> It's certainly undefined somewhere in "htsback.c" before 
the
> call of "hts_htmlcheck_xfrstatus(&back[p])";

The "adr" member is only valid if "is_write" is == 0
Otherwise, the file is streamed directly on disk, without 
being stored in memory, and stored using the "out" (FILE*) 
member, in the file back[p].url_sav (back[p].r.out == fopen
(back[p].url_sav, "wb"))