Develop Reference

How to locate compressed bits of certain files in a zip archive for further processing?

Context:
To save more space, I want to further compress some files in a zip archive with an algorithm, and other files in same archive with another algorithm. Later I need to revert the process to get the original zip archive, because the zip files are owned by users.
How to locate compressed bits of certain files in a zip archive for further processing?
Language: Guess this kind of code is usually C/C++ for performance, but C# is good too.
OS: Windows Server 2012 R2 or later.
Edit:
I learned that in zip(zlib) format, compressed files are organized in blocks. We should be able to locate the files by searching headers. Still checking on how to code it.

The zip file format is fully documented. e.g. http://www.fileformat.info/format/zip/corion.htm
You can find other sources and descriptions easily.
What you have to do is to read bytes according to the format and you have exact knowledge about where a certain file's compressed bits are. You can find open source libraries for this or you can roll your own in your preferred language.
As a side note, compressing an otherwise compressed file in a zip archive may not worth the efforts.

split zip files to volumes [duplicate]

I need to create spanned (multi-volume) zip files using .Net, but I have been unable to find a library that enables me to do it.
Spanned zip is a zip compressed file that is split among a number of files, which usually have extensions like .z00, .z01, and so on.
The library would have to be open-source or free, because I'm gonna use it for a open source project.
(it's a duplicate to this question, but there are no answers there and I'm not going for ASP specific anyway)

DotNetZip example:
int segmentsCreated ;
using (ZipFile zip = new ZipFile())
{
zip.UseUnicode= true; // utf-8
zip.AddDirectory(#"MyDocuments\ProjectX");
zip.Comment = "This zip was created at " + System.DateTime.Now.ToString("G") ;
zip.MaxOutputSegmentSize = 100*1024 ; // 100k segments
zip.Save("MyFiles.zip");
segmentsCreated = zip.NumberOfSegmentsForMostRecentSave ;
}
if segmentsCreated comes back as 5, then you have the following files, each not more than 100kb in size.
MyFiles.zip
MyFiles.z01
MyFiles.z02
MyFiles.z03
MyFiles.z04
Edited To Note: DotNetZip used to live at Codeplex. Codeplex has been shut down. The old archive is still [available at Codeplex][1]. It looks like the code has migrated to Github:
https://github.com/DinoChiesa/DotNetZip. Looks to be the original author's repo.
https://github.com/haf/DotNetZip.Semverd. This looks to be the currently maintained version. It's also packaged up an available via Nuget at https://www.nuget.org/packages/DotNetZip/

DotNetZip allows you to do this. From their documentation:
The library supports zip passwords, Unicode, ZIP64, stream input and output,
AES encryption, multiple compression levels, self-extracting archives,
spanned archives, and more.

Take a look at the SevenZipSharp library. It supports multivolumes archives.

C# re-zipping Docx after image replace won't open [duplicate]

I have been trying to write a simple Markdown -> docx parser/writer, but am completely stuck with the last part, which should be the easiest: i.e. compressing the folder into a .docx that Word, or any other .docx reader, will recognize.
My parser-writer is irrelevant really: I have this problem if I simply unzip any old Word-produced *.docx and then try to recompress it with the usual compression utilities, giving it the file-ending docx. Is there some mysterious header I should be adding, or do I need a special OPC compression utility, or what?
I don't so much want a tool that will do this, as to figure out what is supposed to be there. It seems to be independent of the WordprocessingML specification.
Needless to say I don't know anything about compression. Everything I can find via Google has to do with fancy utilities you can use in business, but I'm making a little executable that would be GPLd or something, and should work on anything.

The most common problem around manually zipping together Open XML documents is that it will not work if you zip the directory instead of the contents. In other words, the[content_types].xml file, and the word, docProps, and _rels directories need to reside at the root level of the zip file.

Here are steps to unzip my.docx and re-zip:
% mkdir unzipped
% cd unzipped/
% unzip ../my.docx
% zip -r ../rezipped.docx *
% open ../rezipped.docx

The compression algorithm used is "Zip" (Base 64) compression.
7zip seems to offer this, though i have no tested it.

Further to what Mica said, the contents of the ZIP file are organised according to the Open Packaging Convention; cf. Microsoft's Essentials of the Open Packaging Convention.
You can use the .NET System.IO.Packaging to make and manipulate .docx files; this class is implemented in the Mono project.

Alternatives to ZIP for combining many files into one on Windows using .NET

Im looking for methods to combine files including their name and relative path into one single file. A folder disguised as a file. I don't need any compression or encryption. Just the file data including some binary metadata attached to each file.
It would be great if this file was possible to open/inspect/unpack with a standard file browser in Windows such as with regular zip-files.
Yes I could use zip. But I'm researching alternatives and I would prefer a simple method I could implement myself in C#/.NET.
UPDATE
I've researched this some more and came across Microsoft's Structured Storage format. It looked promising at first but it seemes to be an obsolete format, replaced with the Open Package Format. And then I found out about the TAR-format. It seemes to be the most basic format. But I'm not sure yet if I can add any custom metadata to the entries with TAR.
UPDATE
I went with DotNetZip at the end anyway...

Why not use zip? You can use a third party library, like dotnetzip, to make the code easy to write. And, as you mentioned, Windows handles zip files well.

If you have specific reason to search an alternative to ZIP, take a look on virtual file systems, eg. CodeBase File System or our Solid File System. Solid File System lets you add alternate data streams (like in NTFS) or tags (small chunks of binary or text data) to each file or directory. And with OS edition of SolFS you can make the filesystem visible to Windows (including Explorer and third-party applications).
I must admit that while virtual file systems are easy to use (easier than ZIP), they are commercial products (I didn't see free virtual file system implementations yet).

c# file container

I am searching for a way to add several files into one file, much like a Zip file. I need to be able to create a file container on the fly and add several word documents, images and other important files into the container. My criteria is that you don't need to install any additional software on the computer (preferebly only a .DLL file that i can include in my project), that the program is free and that you can encrypt the data.
Anyone know of any good container programs that has support for these 2 criterias or if anyone know any good information about how to create your own container.
Patrick

Does it have to be like a zip file, or can it be a zip file?
Are you using .NET Framework 3.0 or 3.5? If so, look at
System.IO.Packaging.ZipPackage
This discussion has a section about it.
In addition to DotNetZip (licensed with Microsoft Public License) that Jay Riggs mentions, there's SharpZipLib (licensed with GPL). Whichever you choose, be sure the terms of the license match your understanding of the word "free".
If you can use ZipPackage, one benefit is that you don't need to think about license terms (beyond those of developing any other .NET app).
EDIT: DotNetZip and SharpZipLib support encryption. I don't see that ZipPackage does, but you could look at System.IO.Packaging.EncryptedPackageEnvelope.

I used DotNetZip in a project and it worked really well. I would recommend using it. It supports encryption and is easy to use.
http://www.codeplex.com/DotNetZip

User .Net GZipStream class(System.IO.Compression namespace.) to compress and decompress files. You can find more information on
MSDN Link
GZIP Compression
I have personally used this technique to decomress .zip file. Click Here