10.4 Isolated Storage

The .NET Framework's isolated storage classes create and manipulate data compartments that are unique to a user and an assembly. For example, suppose that the user joe runs the .NET application someapp.exe. If someapp.exe uses isolated storage to create directories and files, the .NET runtime guarantees that another program (such as anotherapp.exe) cannot access those files, even if joe runs anotherapp.exe. Further, if another user, bob, runs someapp.exe, he won't be able to access the files that someapp.exe created when joe ran it.

Isolated storage is limited by a quota, so even if it's manipulated by untrusted mobile code, you don't need to worry about that code performing a denial-of-service attack by filling your disk with useless data.

Where does isolated storage live? This depends on your operating system, but in Windows 2000 and XP, it is either found in \Documents and Settings\<username>\Local Settings\Application Data\Microsoft\IsolatedStorage (the nonroaming profile) or in \Documents and Settings\<username>\Application Data\Microsoft\IsolatedStorage (the roaming profile). For other operating systems, such as Windows NT 4.0 or Windows 98, see Introduction to Isolated Storage in the .NET Framework SDK documentation.

10.4.1 Reading and Writing Isolated Storage

To create or access a file in isolated storage, create an instance of IsolatedStorageFileStream (pass in the desired filename and combination of FileMode constants). If your assembly doesn't currently have an area of isolated storage set up, .NET creates it at this time. The following example creates a new file in isolated storage, writes some data to it, and then displays the contents of that file:

using System;
using System.IO;
using System.IO.IsolatedStorage;
class Isolated {
  static void WriteToIS( ) {
    // Create a file in isolated storage
    IsolatedStorageFileStream stm =
      new IsolatedStorageFileStream("test.txt", FileMode.Create);
    // Write some text to the stream
    StreamWriter sw = new StreamWriter(stm);
    sw.WriteLine("Hello, World");
    sw.Close( );
    stm.Close( );
  }
  static void ReadFromIS( ) {
    // Open an existing file in isolated storage
    IsolatedStorageFileStream stm =
      new IsolatedStorageFileStream("test.txt", FileMode.Open);
    // Read the file
    StreamReader sr = new StreamReader(stm);
    string s = sr.ReadToEnd( );
    sr.Close( );
    stm.Close( );
    Console.WriteLine(s);
  }
  static void Main( ) {
    WriteToIS( );
    ReadFromIS( );
  }
}

After running this sample you will find the resulting file in the appropriate IsolatedStorage folder for your operating system, as described in the previous section.

10.4.2 Enumerating the Contents of Isolated Storage

The .NET Framework includes the storadm.exe utility for listing (/LIST) the current user's isolated storage or for removing (/REMOVE) all of the user's isolated storage.

You can also access the current user's stores using IsolatedStorageFile. Use the static IsolatedStorageFile.GetEnumerator( ) method with an argument of IsolatedStorageScope.User to enumerate all the isolated storage for the current user. Once you have a store, you can inspect it or modify it, or open one of the files it contains by passing the store to the IsolatedStorageFileStream constructor.

using System;
using System.Collections;
using System.IO;
using System.IO.IsolatedStorage;
using System.Security.Policy;
class EnumIsolated {
  static void Main( ) {
    // Get all the current user's isolated stores
    IEnumerator ie =
      IsolatedStorageFile.GetEnumerator(IsolatedStorageScope.User);
    while (ie.MoveNext( )) {
      IsolatedStorageFile isf = (IsolatedStorageFile) e.Current;
      // Find the location of the associated assembly
      Url url = (Url)isf.AssemblyIdentity;
      Console.WriteLine("Assembly: {0}", url.Value);
      Console.WriteLine("Size: {0}", isf.CurrentSize);
      // List all the files in the store
      Console.WriteLine("Files:");
      string[ ] files = isf.GetFileNames("*");
      foreach (string file in files) {
        IsolatedStorageFileStream isfs = 
          new IsolatedStorageFileStream(file, FileMode.Open, isf);
        Console.WriteLine(" {0}\t{1} bytes", file, isfs.Length);
      }
    }
  }
}