Setting the file access rule of a file with C# .NET

When creating a new file you can set the access control rule for it in code. There are a couple of objects to build the puzzle.

The FileInfo class, which describes a file in a directory, has a SetAccessControl method which accepts a FileSecurity object. The FileSecurity object has an AddAccessRule method where you can pass in a FileSystemAccessRule object. The FileSystemAccessRule object has 4 overloads, 2 of which accept an IdentityReference abstract class. One of the implementations of IdentityReference is SecurityIdentifier. SecurityIdentifier in turn has 4 overloads where the last one is probably the most straightforward to use.

  • WellKnownSidType: an enumeration listing the commonly used security identifiers
  • A domainSid of type SecurityIdentifier: this can most often be ignored. Check out the MSDN link above to see which WellKnownSidType enumeration values require this

The following method will set the access control to “Everyone”, which is represented by WellKnownSidType.WorldSid. “Everyone” will have full control over the file indicated by FileSystemRights.FullControl and AccessControlType.Allow in the FileSystemAccessRule constructor:

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5 ways to compress/uncompress files in .NET

There are numerous compression algorithm out there for file compression. Here come 5 examples with how-to-do links from this blog.

Compressing individual files

The following algorithms can be used to compress a single file. E.g. source.txt will be compressed to source.txt.gz.

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Monitor the file system with FileSystemWatcher in C# .NET

In this post we’ll look at how you can use the FileSystemWatcher object to monitor the Windows file system for various changes.

A FileSystemWatcher object enables you to be notified when some change occurs in the selected part of the file system. This can be any directory, such as “c:\” or any subdirectory under the C: drive. So if you’d like to make sure you’re notified if a change occurs on e.g. “c:\myfolder” – especially if it’s editable by your colleagues – then FileSystemWatcher is a good candidate.

Consider the following Console application:

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How to partially read a file with C# .NET

Say you have a large file with a lot of text in it and you need to find a particular bit. One way could be to read the entire text into memory and search through it. Another, more memory-friendly solution is to keep reading the file line by line until the search term has been found.

Suppose you have a text file with the following random English content:

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How to compress and decompress files with GZip in .NET C#

You have probably seen compressed files with the “gz” extension. These are files that hold a single compressed file according to the GZIP specifications.

GZip files are represented by the GZipStream object in .NET. It’s important to note that the GZip format doesn’t support adding multiple files to the same .gz file. If you need to insert multiple files in a GZip file then you’ll need to create a “tar” file first which bundles the individual files and then compresses the tar file itself. The result will be a “.tar.gz” file. At present tar files are not supported in .NET. They are supported by the ICSharpCode SharpZipLib library available here. We’ll look at tar files in another post soon.

With that in mind let’s see how a single file can be gzipped:

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Using isolated storage for application-specific data in C# .NET

There’s a special storage location for a .NET application on Windows that is allocated to that application. It’s called isolated storage and it’s an optimal place to store files by an application that doesn’t have full access to the file system. Writing to and reading from isolated storage doesn’t require any extra security check. An application without full access to the file system will be able to use its allocated slot in isolated storage and nothing else. It’s an ideal mechanism for storing e.g. application state.

However, don’t confuse isolated storage with file security. It is still a “normal” location on disk with a file path. A typical location is under users/[username]/appdata/local. Therefore you or full-trust applications can still find and modify the files saved in isolated storage. However, limited-trust applications won’t be able to access any other part of the file system.

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Creating temporary files on Windows using C# .NET

It’s trivial to create a temporary file using the Path class in .NET. Let’s first see how to find the path to the current user’s temp folder:

string tempFolderPath = Path.GetTempPath();

In my case it returns C:\Users\andras.nemes\AppData\Local\Temp\ which is the same as the value of the TEMP environment variable at the user level on my PC.

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