make auto-compress-mode only listing tarballs instead of depressing

make auto-compress-mode only listing tarballs instead of depressing

[Amos Bird]

When opening a ~40MB zip file in emacs, it takes 5 seconds to load 
the dired-like buffer. However, `7z l <tarball>` returns 
instantly. Is it possible to customize auto-compress-mode so that 
only file listing is applied instead of fully decompression?

Regards,

--
Amos Bird
amosbird@gmail.com

Re: make auto-compress-mode only listing tarballs instead of depressing

[Eli Zaretskii]

> From: Amos Bird <amosbird@gmail.com>
> Date: Fri, 22 Feb 2019 17:53:21 +0800
> 
> When opening a ~40MB zip file in emacs, it takes 5 seconds to load 
> the dired-like buffer.

I just tried this with a 49MB zip file, and it took me less than 2
sec.  I tried a 495MB file, and it took 5.5 sec to show the listing.
Do you see those 5 sec in "emacs -Q"?  If so, is your box particularly
slow?

> However, `7z l <tarball>` returns instantly. Is it possible to
> customize auto-compress-mode so that only file listing is applied
> instead of fully decompression?

If you are talking about arc-mode.el, it already decodes only the
directory part of the zip file, without uncompressing the entire
archive.  It's definitely slower than 7z, because the decoding is done
in Lisp, so if we want to speed it up even further, I'd suggest to
write a module in C.  However, I wonder why you see such a long time.