Re: [AD] Custom packfiles

[Peter Wang <tjaden@xxxxxxxxxx>]

Chris wrote:

> Peter Wang wrote:
>
> > > > nor can you use pack_fopen_chunk() on
> > > > vtable-packfiles.
>
> Well, as has been mentioned before, I think Allegro's default pack_* 
> functions should be implemented as a vtable that's always used for 
> pack_fopen(). pack_fopen_chunk can simply check that the vtable is 
> Allegro's, and fail if it isn't. Yeah, this would mean the 
> pack_*_chunk would be "special", but since they're of limited use 
> outside of Allegro's datafiles anyway, I can deal with that. People 
> can easilly support zips or their own archive format anyway.


Note my patch already made pack_*_chunk do this check already.  And you 
know what I think about packfile_password()-style semantics for 
pack_fopen().

> However, one thing I would like is for the vtable to contain pf_open 
> and pf_close methods. That would potentially cut down on a lot of 
> duplicate code. So the user could do, for instance:
>
> struct mystruct data = {
>    "myfile.wad", 0
> };
> PACKFILE *pf = pack_fopen_vtable(&my_vtable, &data);
>
> Then the my_vtable.pf_fopen function would do the actual opening of 
> the specified file "myfile.wad and could seek to a specific object 
> (specified through an index 0 in this case) in the file.


I don't see how it cuts down on duplicate code.  Say you're going to 
write a wrapper like:

   PACKFILE *load_wad_object(const char *filename, int index);

With your style:

   PACKFILE *load_wad_object(const char *filename, int index)
   {
      struct mystruct *data = malloc(sizeof *data);
      data->filename = filename;
      data->index = index;
      return pack_fopen_vtable(&my_vtable, &data);
   }

   int my_fopen(struct mystruct *data)
   {
      data->fd = open(data->filename);
      seek_to_object(data->fd, data->index);
      return ok;
   }

With my style:

   PACKFILE *load_wad_object(const char *filename, int index)
   {
      int fd = open(filename);
      struct mystruct *data = malloc(sizeof *data);
      data->fd = fd;
      seek_to_object(data->fd, index);
      return pack_fopen_vtable(&my_vtable, &data);
   }

i.e. with my style pack_fopen_vtable() is only called after the rest of 
the opening process is complete.  You don't have to stuff input 
arguments into a struct just to get it through to pf_fopen.



BTW, I found that if we drop support for old-style packfile encryption 
then the LZSS compression/decompression code can be completely decoupled 
from packfiles (I have done it in my local copy).  What do you guys 
think about that?  New-style encryption was introduced in 3.9.30.

Peter