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https://issues.apache.org/jira/browse/COR-18?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14282064#comment-14282064
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Peter Kelly commented on COR-18:
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Regarding handling of paths and directories: The necessary logic for this is
already implemented for OPC (Open Packaging Conversions, used by OOXML) in
filters/ooxml/common/OPC.c. The header defines several classes, including
OPCPackage, OPCPart, and OPCRelationship which provides access to and
manipulation of the package OPC level of abstraction rather than that of a
directory hierarchy (within a zip or elsewhere).
Relative paths are handled appropriately. At load time, the function which does
this, OPCPackageReadRelationships, calls through to DFPathResolveAbsolute to
ensure the correct path is obtained. At save time, paths are all written as
absolute.
I've just put up a description of the DFStorage API
(https://cwiki.apache.org/confluence/display/Corinthia/DFStorage) which is sort
of like a virtual filesystem layer, in that it allows us to store a set of
files in various places (currently a directory on the filesystem, a zip file,
or in memory only). This deliberately works on a "flat" model where there's no
inherent concept of directories - the aim being to keep the api simple.
However, one can include path separators in filenames, so it's still possible
to store files at different points in a hierarchy.
The only limitation to this API is that it doesn't support "whole of directory"
operations like moving, copying, creating, deleting etc. This was a deliberate
decision, make to cut down on the complexity of code - there were quite a lot
of places where code would e.g. check for the existence of an images directory
and create it if necessary before adding a .jpg file to a docx package. For our
particular requirements, this was unnecessary complexity - so now you can
simply give it a path name for a file and it will take care of the rest.
> Replacing MiniZip
> -----------------
>
> Key: COR-18
> URL: https://issues.apache.org/jira/browse/COR-18
> Project: Corinthia
> Issue Type: Bug
> Components: DocFormats - platform
> Environment: source
> Reporter: jan iversen
> Assignee: jan iversen
> Priority: Blocker
> Fix For: 0.5
>
>
> MiniZip is a bit thin and, because of some changes needed, it might be better
> to replace it in the DocFormats/3rdparty/external/ folder, as @peterkelly
> observes at COR-26 (comment)
> EASY STEPS
> For now, it might be desirable to simply replace the current code with
> MiniZip 1.1 from http://www.winimage.com/zLibDll/minizip.html
> Since it is a simple dependency, this should work fine so long as there are
> no breaking API changes in between 1.0h and 1.1.
> EVENTUALLY?
> It would be good to have something behind a stable API that permits random
> access for reading file streams as Peter suggests. Ideally, that API would be
> aligned around the Document Container File (DCF) profile of the official
> PKWare specification that is used commonly among ePub, ODF, and the Open
> Packaging Conventions (OPC) used in OOXML and elsewhere. I don't know what
> the latest status of that profile is at ISO/IEC JTC1 SC34, but it will become
> a common international specification for these specialized usage of Zip as a
> compound document-format container file.
> There are other places to look for ideas and possible sources of reusable
> code and API considerations, including in Apache OpenOffice, the Apache ODF
> Toolkit (using Java). , and the Microsoft open-sourcing of its OOXML-access
> layer (in .NET I think). And the Microsoft platform has some native support
> that it might be useful to be able to rely on in Windows-targeted builds.
> There is also a CodePlex LibOPC project that is C code under a BSD-form
> license at https://libopc.codeplex.com/ One interesting feature of LibOPC
> that may interest Apache OpenOffice folk (i.e., @janiversen) is a python
> script for generating Visual Studio projects that can be used for
> manipulating and building on Windows.
> One caveat. For ingesting Zip-based document files, there needs to be a fair
> amount of code to ensure resiliency and defense against DOS-ing of
> applications with malformed document files. That may have to be grown, with
> attention to the code footprint on limited-capacity devices (where presumably
> some of the heavy-lifting is off-loaded to the cloud). It is an interesting
> feature of the OPC specification is that it is also designed to support
> remoting of the document streams in a way where there is no requirement that
> a Zip file be transferred to the client. That may be very much eventually,
> but it is useful to think about having an API that would allow for that
> underneath. [Ed.Note: COR-31 is related to this.]
> LEST WE FORGET?
> Although this is all .NET-fu, there may be useful ideas on this project,
> https://github.com/OfficeDev/Open-Xml-Sdk
> as a source of ideas (and some of the system-level dependencies may have
> Native Windows counterparts as well). This might be useful for mining for
> other ideas higher up in the API modeling too.
> ---
> I didn't think to mention POI and whatever they use as a model close to the
> Zip packages.
> I didn't realize until looking at the proposal to become an Apache incubator
> project that the sources for minizip and tidy-html5 are not pristine. It
> would be good to reconstruct the modification process and leave more
> footprints if the changes are not in the repository here. (Actually, it would
> be good to reconstruct the modification anyhow, but diffs from git would be
> helpful.)
> I'm thinking that there is no hurry to replace these in early stages. If a
> better API is desired, the first step of getting that in place would be to
> build a shim that goes from that API to anything hand at first, such as
> minizip or some other library, and worry about fit and performance later.
> jan:
> POI is in java, so they have other packages available.
> I am currently working on expanding the platform part to also include zip and
> html, so that we can change the libraries at a later stage. I think your idea
> of using libOPC is valid and interesting...you, peter and svante knows better
> if it fits to the project.
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