[delphizip] RE : New format - internal directory structure
- From: "James Turner" <james.d.h.turner@xxxxxxxxxxxx>
- To: <delphizip@xxxxxxxxxxxxx>
- Date: Wed, 6 Nov 2002 12:01:58 -0000
In the Zip format, both the file headers and directory records contain the
whole path. This makes the notional movement of files from one directory to
another rather tricky since it means rewriting the whole archive.
Suppose, the central directory contained an indexed list of paths
(directories). A non-zero value for this index in a directory record would
indicate which directory the file currently belonged to. Of course, each path
entry would have to consist of three fields being
ParentIndex : Word32; { index of parent directory }
Length : Word16;
Name : variable length char string;
The file header need only contain the original file name. All rename/path
changes could be stored in the central directory entry exclusively. This means
that the name located in a central directory entry might be different to that
stored in the corresponding file header. This is ok but some system of error
checking would probably be a good idea.
If implemented archives would be smaller (not much) and renaming/moving files
would involve only the rewriting of the central directory. Of course, a Z++
program could optionally rewrite the whole archive as is done with zip
archives, but it would no longer be necessary. This also means that empty
directories would no longer need to be represented by zero-length files.
Further, if all the files were moved out of one directory into another, the
empty directory could be easily deleted.
This still leaves the thorny issues of adding/deleting files (space recovery
and fragmentation) but it is potentially a step towards creating a versatile
archive format.
-- James Turner --
http://www.skaro.net
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