ISOLATED STORAGE

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ISOLATED STORAGE

• by
• Santosh Reddy Vuppala

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OUTLINE

• Introduction
• Need for Isolated Storage
• Levels of Isolation
• Implementation
• Limitations
• Conclusion

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Introduction

• Many applications need to write User preferences
  and Application State to a persistent store so
  that it's available each time the application
  runs.
• Potential Stumble blocks
• Your code might lack permission to write to an
  arbitrary file.
• The user may lack permission to write data to an
  arbitrary file.
• Past Approaches .INI file, Windows Registry and
  the Config file.
• .INI file Limitations
• INI files had no way to represent hierarchical
  information.
• There was no standardized and safe place to keep
  INI files.
• INI files had a size limitation.

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Introduction

• Windows Registry Limitations
• Because the registry is globally accessible, a
  carelessly written install routine or
  application can bollix up the registry data for
  other applications and render them unstable or
  unusable.
• The registry tends to swell to a huge size
  with duplicated and unneeded information, and a
  large registry slows down the entire system.
• It's difficult to find or edit information
  in the registry.
• Config File Limitations
• Is that these config files are intended for
  read-only information.

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Need For Isolated Storage

• Isolated storage provides a controlled and
  structured mechanism through which code can write
  data to the hard drive in a way that prevents
  access by other users and managed applications.
• Isolated storage provides a more secure data
  storage alternative than granting code direct
  access to selected areas of the hard drive .
• In addition, isolated storage can leverage the
  capabilities of Windows-roaming user profiles,
  ensuring that a user's data is available to them
  regardless of which machine they use.

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What is a Store?

• A store is a compartment within isolated storage
  that has an identity derived from the identity of
  the user and code that created it.
• Before managed code can save data to isolated
  storage, it must obtain a store.
• The use of stores means that each time code runs,
  it has access to any data that it previously
  saved to isolated storage. Because different
  applications run by the same user have different
  identities, they each obtain unique stores.

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• A store acts as a complete virtual file system.
  You can create and delete directories and files
  within a store, and read and write data to the
  files in the store.

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Levels of Isolation

• Isolation by user and assembly
• --With user and assembly isolation, one piece
  of evidence from the assembly is used.
• Isolation by user, assembly, and application
  domain
• --When isolating by user, assembly, and
  application domain, isolated storage uses one
  piece, of evidence from the assembly and one from
  the application domain for the stores identity

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Isolation by User and Assembly

• When code obtains a store isolated by user and
  assembly, isolated storage returns a store with
  an identity based on the current user and the
  assembly that made the call to obtain the store.
• Isolation by user and assembly enables an
  assembly used in multiple applications to share
  data across those applications.
• Used inappropriately, isolation by user and
  assembly can cause data leaks between
  applications.

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Isolation by User, Assembly and Application Domain

• When code obtains a store isolated by user,
  assembly, and application domain, isolated
  storage returns a store with an identity based on
  the current user, the assembly that made the call
  to obtain the store, and the application domain
  in which the assembly is loaded .
• Isolation by user, assembly, and application
  domain limits the ability of an assembly to share
  or leak data across multiple applications .

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Obtaining a Store

• Two static methods of the IsolatedStorageFile
  class provide the simplest and most common way of
  obtaining a store
• GetUserStoreForAssembly ,
  GetUserStoreForDomain
• // Obtain a store isolated by user and assembly
• IsolateStorageFile iso1 IsolatedStorageFile.Get
  UserStoreForAssembly( )
• // Obtain a store isolated by user, assembly, and
  application domain IsolateStorageFile iso2
  IsolatedStorageFile.GetUserStoreForDomain( )

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Obtaining a Store

• The static IsolatedStorageFile.GetStore method
  also obtains a store, but allows the caller to
  specify the scope and identity of the store to
  obtain.
• User Assembly ? Requests a store isolated by
  user and assembly, the same as that returned by
  the GetUserStoreForAssembly method.
• User Assembly Domain ? Requests a store
  isolated by user, assembly, and application
  domain, the same as that returned by the
  GetUserStoreForDomain method.
• Roaming User Assembly ? Requests a roaming
  store isolated by user and assembly.
• Roaming User Assembly Domain ? Requests a
  roaming store isolated by user, assembly, and
  application domain

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• // GetStore equivalent of GetUserStoreForAssembly
  
• IsolatedStorageFile iso1 IsolatedStorageFile.Ge
  tStore( IsolatedStorageScope.User
  IsolatedStorageScope. Assembly, null, null )
• // GetStore equivalent of GetUserStoreForDomain
• IsolatedStorageFile iso2 IsolatedStorageFile.Ge
  tStore( IsolatedStorageScope.User
  IsolatedStorageScope.Assembly
  IsolatedStorageScope.Domain, null, null )
• // Get a roaming store isolated by user and
  assembly. Specify new Url evidence for the
  assembly identity
• IsolatedStorageFile iso3 IsolatedStorageFile.Ge
  tStore( IsolatedStorageScope.User
  IsolatedStorageScope.Assembly
  IsolatedStorageScope.Roaming, null, new
  Url(_at_"http//test.com") )

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Creating Directories

• The basic way of doing it
• public void CreateDirectory( string dir )
• To create more than one level of the directory
  hierarchy in a single call.
• IsolatedStorageFile iso IsolatedStorageFile.GetU
  serStoreForDomain( ) iso.CreateDirectory(_at_"Dir1\D
  ir2")
• iso.CreateDirectory("Dir1/Dir3")

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Creating, Reading and Writing Files

• The IsolatedStorageFileStream class represents a
  file in a store
• public IsolatedStorageFileStream(
• string path,
• FileMode mode,
• FileAccess access,
• FileShare share,
• int bufferSize,
• IsolatedStorageFile isf )
• mode represents either open or create
• access represents either read or write
• The isf argument is a reference to the
  IsolatedStorageFile in which to create or open
  the file.

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Deleting Files and Directories

• The files and directories from a store can be
  deleted through the methods of the
  IsolatedStorageFile object that represents the
  containing store.
• Both the DeleteDirectory and DeleteFile methods
  take a single String argument that specifies the
  fully qualified name of the file to delete .
• public void DeleteDirectory( string dir )
• public void DeleteFile( string file )

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Delete Stores

• To delete a store, we use the Remove method of
  the IsolatedStorageFile class.
• Remove has two overloads, with the signatures
  shown here
• public override void Remove( )
• public static void Remove(
  IsolatedStorageScope scope )
• The scope argument can take any of these
  values
• User ? Removes all nonroaming stores for
  the current user
• Roaming User ? Removes all roaming stores
  for the current user

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Limitations of Isolated Storage

• Here are some situations when the use of isolated
  storage is inappropriate
• When valuable or secret data is used
• When data between users is shared
• When managed and nonmanaged code need application
  access
• When there is no roaming-profile support
• When used as a primary file store
• When large amounts of data are used

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References

• http//www.codeproject.com/dotnet/IsolatedStorage.
  asp
• http//www.dotnetdevs.com/articles/IsolatedStorage
  .aspx
• http//www.codeguru.com/csharp/csharp/cs_data/arti
  cle.php/c4225/

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• Questions?