I'm working on application that must enrypt and zip files. So, I create some data in memory (text, binary or whatever), encrypt it and save to disk (file1 and file2). The I call e.g. "zip out.zip file1 file2 ".
I do not want to save this files to disk, but immediately create zip and pack these files from memory.
How should I do that?
Thanks a lot!
You could try to use the zlib library to be able to create zip files from memory buffers.
The boost:iostreams could also be a good solution.
For zlib there is an extension for zip called minizip in the contribs. For minizip you can find code to work with in-memory buffers on the authors page:
Justin Fletcher wrote a very simple implementation of a memory access method for the ioapi code (ioapi_mem_c.zip).
Note that you must compress first and then encrypt. Encrypted data can't be compressed anymore.
Interestingly enough, I wasn't able to find a library to create ZIP files from C. zlib only allows to (de-)compress individual entries in a ZIP archive.
It comes with contrib/minizip; maybe that can get you started.
Related
I'm looking to replace the zip library that I am using in a small utility with something a bit better.
One of the deficiencies in the library I am currently using is that it doesn't appear to validate zip file very well - I can corrupt the file by changing random characters and the library doesn't notice.
I am looking for a C++ zip library that has a function to validate the zip file without extracting all the files in the library.
Someone recommended ziplib to me, but I don't see anything in there about checking the integrity of a zip library.
Does anyone know if ziplib has this capability? Or have a better recommendation?
Libraries like libzip and libarchive allow you to read archive entries a chunk at a time. You can simply read the entire archive to verify it, repeatedly overwriting the same buffer in memory with the decompressed data and thereby discarding it.
I have to read a dat-file byte by byte from a zip-file in a char[] buffer. The zip-file contains only one dat-file. I guess unzip chunk by chunk would be good. I am using Visual Studio 2013 with c++.
I have found zip-utils (http://www.codeproject.com/Articles/7530/Zip-Utils-clean-elegant-simple-C-Win), would this be ok, because its nearly 10 years old? Would Minizip be a good way? I guess zlib alone would not be enough for this use case, right?
My question is, whats the best way to do the unzipping? I have no experience with handling zip-files and would like to hear a suggestion by somebody with experience.
Thank you,
Friedrich
Minizip would work. Please notice that it still requires zlib source code to link with.
A zip file is not just chunks of zlib compressed content.
It's an archive.
There is a directory header, and per element header you must decode too even if the archive only contains a single file. Typically, the header will tell you from which offset in the zip file you'll find your DAT compressed content. Then you'll likely use zlib to decode chunk by chunk starting at the given offset.
Please notice also that zip file format does not always imply zlib as a compressor (you can have many different compressor). If you master the code that create the zip file, it's not an issue. But if it comes from hostile user, then you should rely actually check the compressor used and assert it's zlib else you should deny decompressing the file because you'll not be able to do so.
i working on ClamAV antivirus database.
ZMD one of clamav database file who store information about malice's zip file.
i need to get this information from zip file but if possible not use any component
is encryption.
normal size
compressed size
CRC32
compression method
please help me.
You can use unzip -l to list the contents or you can write your own zip format decoder to extract the information from the headers. The format is documented in the .ZIP File Format Specification.
I have a rather large ZIP file, which gets downloaded (cannot change the file). The quest now is to unzip the file while it is downloading instead of having to wait till the central directory end is received.
Does such a library exist?
I wrote "pinch" a while back. It's in Objective-C but the method to decode files from a zip might be a way to get it in C++? Yeah, some coding will be necessary.
http://forrst.com/posts/Now_in_ObjC_Pinch_Retrieve_a_file_from_inside-I54
https://github.com/epatel/pinch-objc
I'm not sure such a library exists. Unless you are on a very fast line [or have a very slow processor], it's unlikely to save you a huge amount of time. Decompressing several gigabytes only takes a few seconds if all the data is in ram [it may then take a while to write the uncompressed data to the disk, and loading it from the disk may add to the total time].
However, assuming the sending end supports "range" downloading, you could possibly write something that downloads the directory first [by reading the fixed header first, then reading the directory and then downloading the rest of the file from start to finish]. Presumably that's how "pinch" linked in epatel's answer works.
I did search for this topic, but I didn't find any relevant clue for this.
Can anyone give me some tips or demo code that can solve the problem?
Thanks in advance.
---FYI---
What I wanna do here is to zip files and upload to remote PC.
I think it'll take the following steps:
a) initialize a zipped file head and send to remote PC and save that zipped file head.
b) open file to read a portion of file data and zip the file data locally.
c) send zipped data through a pipe (tcp or udp for example) to remote PC.
d) save the data from pipe, which is zipped, on the remote PC.
e) if there are multiple files, come back to b)
e) when all files is zipped and transferred to remote PC, then close zipped file.
Two question here:
a) compress/decompress
b) File format
Thanks guys!
zlib zips a single stream. If you want to zip multiple files, you need to do one of two things:
Define a format (or use an existing format) that combines multiple files into one stream, then zip that; or
Zip each file individually, then use some format to combine those into one output file.
If you take the first option, using the existing tar format to combine the files, you will be producing a .tar.Z file which can be extracted with standard tools, so this is a good way to go. You can use libtar to generate a tar archive.
I have built a wrapper around minizip adding some features that I needed and making it nicer to use it. Is does use the latest c++11 and is developed using Visual Studio 2013 (should be portable, but i havent tested it on unix)
There's a full description here: https://github.com/sebastiandev/zipper
but is as simple as you can get:
Zipper zipper("ziptest.zip");
zipper.add("somefile.txt");
zipper.add("myFolder");
zipper.close();
you can zip entire folders, streams, vectors, etc. Also a nice feature is doing everything entirely in memory.