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Wesley Harris
Wesley Harris

Cannot Read That As A Zip File Dotnetzip

When reading a zip file, there are several options an application can set, to modify how the file is read, or what the library does while reading. This class collects those options into one container.Pass an instance of the ReadOptions class into the ZipFile.Read() method.

cannot read that as a zip file dotnetzip

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Playing with SSIS I normally have to read flat files that come in zip format. The standard procedure here is to launch winzip, decompress the file, read it with a flat file adapter and then delete the uncompressed file. This behaviour generates a lot of useless I/O on temporary disks to decompress a file that will be soon deleted.

Another way of solving the problem is to have a look at DotNetZip library. A very smart programmer wrote a library that makes opening zip files very easy using .NET. He also added in version 1.6 a great function: OpenReader. You can open a zip file, look into its entries and open a stream reader on it.

.NET has multiple built-in APIs to create ZIP files. The ZipFile class has static methods to create and extract ZIP files without dealing with streams and byte-arrays. ZipFile is a great API for simple use-cases where the source and target are both on disk. On the other hand, the ZipArchive class uses streams to read and write ZIP files. The latter is more complicated to use but provides more flexibility because you can accept any stream to read from or write to whether the data comes from disk, from an HTTP request, or from a complicated data pipeline.

After getting some hints from David Fowler, I found a way to send the file to the client without a MemoryStream. He pointed me towards pipelines which is an interesting API for writing to and reading from pipes at the same time. You could create a Pipe, get the .Writer, and use the .AsStream() to get a stream to replace the MemoryStream. You could then use the .Reader to read the data as it becomes available and write it to the body.

The biggest downside of the first version is that the entire ZIP file is being stored in memory as it is generated and then send to the client. As more bot files are stored in the archive, more memory is accumulated.On the other hand, the second version writes file by file to the BodyWriter and ASP.NET Core takes care of streaming the data to the client. This prevents the data from accumulating in memory.The difference is huge, especially with lots of large files. The memory graph has been recorded when using lots of large files to make the difference more apparent:

The code for sending the ZIP file to the browser using Razor Pages is essentially the same.The only difference is that you're inheriting from a PageModel instead of a Controller, and you have to follow the naming convention of Razor Pages handler methods which results in the method name OnGetDownloadBots.

The ZipArchive wraps any stream to read, create, and update ZIP archives whether the data is coming from disk, from an HTTP request, from a long data-pipeline, or from anywhere else. This makes ZipArchive very flexible and you can avoid saving a ZIP file to disk as an intermediary step. You can send the resulting stream to the browser using ASP.NET MVC, Razor Pages, and endpoints as demonstrated above.

git archive only includes files that are stored in git, and excludes ignored files and git files. This helps keep your source bundle as small as possible. For more information, go to the git-archive manual page.

The graphical user interface (GUI) on Mac OS X and Linux-based operating systems does not display files and folders with names that begin with a period (.). Use the command line instead of the GUI to compress your application if the ZIP file must include a hidden folder, such as .ebextensions. For command line procedures to create a ZIP file on Mac OS X or a Linux-based operating system, see Creating a source bundle from the command line.

As noted in the list of requirements above, your source bundle must be compressed without a parent folder, so that its decompressed structure does not include an extra top-level directory. In this example, no myapp folder should be created when the files are decompressed (or, at the command line, no myapp segment should be added to the file paths).

If you need to manually create a source bundle for your .NET application, you cannot simply create a ZIP file that contains the project directory. You must create a web deployment package for your project that is suitable for deployment to Elastic Beanstalk. There are several methods you can use to create a deployment package:

Title: Use the DotNetZip library to compress and decompress files in C#BackgroundNormally I don't like to require third-party libraries. I don't know what tools you have loaded on your system and I don't want to assume you can load new tools without creating conflicts. If third-party tools get out of synch, it can also be hard to upgrade appropriately to get them all working again.However, this tool seems worth adding to your toolkit. The .NET Framework comes with a System.IO.Compression.GZipStream class that lets you compress and decompress files. Unfortunately it works only with GZip files (with a .gz extension) not regular .zip files. You can open these files with many other third-party tools, but the Windows operating system doesn't let you browse them the way it does Zip files. (I don't see the logic in providing a way to make compressed files that the operating system can't read. Perhaps it's a licensing issue.)You can build true Zip files with the System.IO.Packaging namespace, but Microsoft has done a terrible job with it. It requires all sorts of strange URIs, resource and document parts, relationships, and running data through streams when you should just be able to add and remove objects. (It really seems like it was designed by someone who's never needed to do this in real life. Possibly the same people who designed WPF, particularly WPF bitmaps.)Installing DotNetZipThe DotNetZip library, which is free, provides .NET managed classes that you can use from C# to compress and decompress true Zip files. This example only shows a couple of the library's features.To use it, start a new project. In Solution Explorer, right-click on References and select Manage NuGet Packages. On the Browse tab, search for DotNetZip, click it, and then on the right click Install. I had to fiddle with this a bit to get it to install because it seemed confused about .NET Framework version. If you have problems, you may need to change the version that your project is targeting.To make using the library easier, add this using statement:using Ionic.Zip;

Using the LibraryTo add a file to an archive, create a ZipFile object representing the Zip file. Then use the ZipFile object's AddFile method to add the file to the archive, specifying the file's path and the relative path within the archive where the file should be placed.To extract a file from an archive, use the ZipFile class's Read method to open the Zip file and make a ZipFile object representing it. Now you can loop through the file's ZipEntry objects and extract any objects that you want to recover.Using the ExampleTo add a file to a Zip file, enter the Zip file's name. Enter the name of the file you want to add to it and the relative path you want the file to have inside the Zip file. Click the Add to Archive button to add the file to the Zip file.To extract all of the files from the Zip file, enter the directory where you want the files extracted and click Extract Archive.This example only lets you add files to an archive and extract all of the files in the archive. DotNetZip allows you to do other things like dig through a Zip file and extract only certain files. It also has AddProgress and ExtractProgress event handlers to let you know how a long operation is progressing.How the Example WorksThe following code shows how the program adds the file to the archive. The code in the using block is all there is to actually adding the file to the archive. The rest of the code updates the display and handles exceptions.// Add the file to the archive.private void btnAddToArchive_Click(object sender, EventArgs e) try using (ZipFile zip = new ZipFile(txtArchiveName.Text)) // Add the file to the Zip archive's root folder. zip.AddFile(txtFileName.Text, txtPathInArchive.Text); // Save the Zip file. zip.Save(); // Display the file sizes. FileInfo old_fi = new FileInfo(txtFileName.Text); lblOriginalSize.Text = old_fi.Length.ToString("#,#"); FileInfo new_fi = new FileInfo(txtArchiveName.Text); lblCompressedSize.Text = new_fi.Length.ToString("#,#"); MessageBox.Show("Done"); catch (Exception ex) MessageBox.Show("Error adding file to archive.\n" + ex.Message);

The Zip format allows for several different compression methods, but the most common is Deflate. System.IO.Compression includes a DeflateStream class. You'd think that System.IO would include Zip, but... no. The problem is that, while System.IO.DeflateStream can write to a stream, it doesn't write the file headers required for Zip handlers to read them.

Another larger problem to keep in mind is that stream based compression is much less efficient than file based compression. File compression can optimize the compression used based on the content of all included files; stream based compression compresses data as it comes in, so it can't take advantage of data it hasn't seen yet.

One weird side-effect of using the ZipPackage to create Zips is that Packages contain a content type manifest named "[Content_Types].xml". If you create a ZipPackage, it will automatically include "[Content_Types].xml"., and if you try to read from a ZIP file which doesn't contain a file called "[Content_Types].xml" in the root, it will fail.

You'll notice that the compression in my test is not that great. In fact, pretty bad - Notepad.exe got bigger. Binary files don't compress nearly as well as text-based files - for example, I tested on a 55KB file and it compressed to less than 1KB - but the compression in this library doesn't appear to be fully implemented yet. For example, the CompressionOption enum includes CompressionOption.Maximum, but that setting is ignored. Normal is the best you'll get right now.


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