corinthia-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From jan i <j...@apache.org>
Subject Re: Zip madness !
Date Sat, 01 Aug 2015 17:39:07 GMT
On 1 August 2015 at 17:41, Peter Kelly <pmkelly@apache.org> wrote:

> Hi  Jan,
>
> I’ll get to your question in a moment, but I just checked out the
> newZipExperiment branch and noticed that almost all of the source files
> have changed (I was expecting a relatively small diff, with only a few
> files changed). It looks like most of these differences are due to
> reordering the #includes at the top of each source file. If we’re going to
> do this, could we make it a separate commit in master, so it’s easier to
> see exactly what has changed in the zip branch?
>
We are not going to do this, it was me being religious for a moment.

I need a FILE * in the zipHandle structure, and did not like void *

>
> Actually I normally intentionally put system headers after other headers
> in the project, as it helps to detect cases where a custom header depends
> on types declared in a system header, and thus for which importing that
> header (by itself) in a source file would result in compilation errors due
> to the missing references. For example DFBuffer.h has an #include
> <stdarg.h> at the type since some of the functions take the va_list data
> type. If one of us uses such this type in another header which doesn’t have
> #include <stdarg.h>, then any C file that imports it (directly or
> indirectly) has to remember to explicitly include stdarg.h (and that could
> be a *lot* of files, if the header is referenced from lots of places). So
> by placing the any system includes needed by the source file after all
> custom headers, we can pick up on these errors more easily.
>
This is actually how we agreed on it, you will see a newExperiment2 without
these many changes.


>
> Regarding the zip file format, I need to look up on some stuff and will
> get back to you shortly. But I suspect some of the duplication may be
> related to the fact that a zip file is meant to be read backwards. Rather
> than starting at the beginning of the file, reading begins at the end,
> working backwards through the file to find potentially multiple copies of
> the directory listing. This serves two purposes:
>
> 1) You can “modify” the contents of a zip file simply by appending (with
> the compressed content of new/changed files added, and a new directory
> listing including these files, an *not* including any files which have been
> “deleted”, i.e. masked out).
>
> 2) A zip file can be appended to the end of another file format; the most
> common example being self-extracting .exe files. Since .exe files are read
> from the beginning, the program loader on windows doesn’t care about the
> fact that there’s the trailing data at the end. And it’s still a valid zip
> file, since the .exe content at the start is ignored when reading the
> directory listing.
>
> I think you may be aware of some of these details already, and there’s
> some nuances I’ve probably missed. I’m about to have a look through the
> code you currently have in the branch.
>
Painfully aware. I am slowly including code from an old project of mine,
which is soo old that I have forgotten why I did things.

I expect to have the open/read part finished in some hours, otherwise it
will be delayed to monday.

I also have an experimental write (only local, not committed).

Thanks for taking a look. I will write in here when I consider the
open/read ready for master. I would like to move that to master before I do
the write part.

rgds
jan i.

>
> —
> Dr Peter M. Kelly
> pmkelly@apache.org
>
> PGP key: http://www.kellypmk.net/pgp-key <http://www.kellypmk.net/pgp-key>
> (fingerprint 5435 6718 59F0 DD1F BFA0 5E46 2523 BAA1 44AE 2966)
>
> > On 1 Aug 2015, at 4:33 pm, jan i <jani@apache.org> wrote:
> >
> > Hi
> >
> > Does anybody know why zip has a mad inefficient directory structure ?
> >
> > I try to understand the why, but fail.
> >
> > A zip file, contains 1 global directory with information about every
> single
> > file (flat structure, no
> > sub directories, but filenames may contain a "/"). That is logical and
> > expected.
> >
> > BUT in front of every file, there are a local file header, with filename
> > about 3/4 of the information
> > from the global directory. This information seems pure redundant and
> > unneeded.
> >
> > What am I missing here ? on one of my test docx, the local headers are
> > about 10% of the filesize (looong filenames) which could be thrown away.
> >
> > Hope somebody can see what I failed to see.
> > rgds
> > jan i.
>
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message