// Copyright (c) 2006-2009 Nokia Corporation and/or its subsidiary(-ies).

 // All rights reserved.

 // This component and the accompanying materials are made available

 // under the terms of the License "Eclipse Public License v1.0"

 // which accompanies this distribution, and is available

 // at the URL "http://www.eclipse.org/legal/epl-v10.html".

 //

 // Initial Contributors:

 // Nokia Corporation - initial contribution.

 //

 // Contributors:

 //

 // Description:

 // An application can explore the content objects inside a file using the <code>ContentAccess::CContent</code> class.

 // <hr>

 // The Content Access Framework provides a generic mechanism for exploring files that contain multiple

 // content objects. These files are often referred to as archive files. This could

 // be anything from a .ZIP compression archive to a DRM protected archive such as an OMA .DCF file.

 // Inside an archive file, and in addition to the content objects, there will be meta-data or information 

 // associated with the content. This meta-data could include information such as the MIME type of the content, 

 // encryption algorithm, compressed size of the content etc.. This information can be retrieved from the attributes

 // The content and meta-data may also be arranged in a heirachy with container objects grouping 

 // content objects together. A typical archive could have a complex structure like the example shown below:

 // In this situation the file itself can be considered as the top level container. All other content, containers and

 // meta-data are nested inside. 

 // In an archive file applications can quickly search for the content objects they are interested in by using 

 // <code>ContentAccess::CContent::Search()</code>.

 // <hr>

 // Archive files containing several content objects cannot be referred to using just the URI of the file. The Content Access

 // Framework uses a concept of virtual paths to identify content objects within a file. The virtual path is a combination

 // of the file URI and a unique identifier supplied by the agent: 

 // A content file is only ever handled by the agent that recognises it. The unique identifier will never need to be 

 // decoded by anyone other that the agent that generated it, so the format is left for the agent to implement as it sees

 // fit. For instance an OMA DRM agent may put the Content ID (CID) in the \c UniqueId field.

 // The only constraint is that the \c UniqueId must be unique within the file. An application must be able to directly

 // reference a content object just using the <code>UniqueId</code>. 

 // <hr>

 // <b> Virtual Path pointer objects on the Stack </b>

 // The <code>ContentAccess::TVirtualPathPtr</code> is used to point to two descriptors holding the URI 

 // of a file and the <code>UniqueId</code> of a content object within the file. It can also be used to 

 // point to another <code>TVirtualPathPtr</code>. Since it is only a pointer, the original descriptors 

 // used to initalise the <code>TVirtualPathPtr</code> should not be destroyed or modified while the 

 // <code>TVirtualPathPtr</code> is still in use.

 // <b> Virtual Path objects on the heap </b>

 // The <code>ContentAccess::CVirtualPath</code> class stores the file URI and content object <code>UniqueId</code> in its own 

 // descriptors. There is a cast operator that allows the <code>CVirtualPath</code> to be used as 

 // if it were a <code>TVirtualPathPtr</code>.

 // <b> Examples </b>

 // // Open a CContent object to browse the objects inside a file

 // CContent *c = CContent::NewL(_L("C:\file.dcf"));

 // CleanupStack::PushL(c);

 // // Create an array to store the embedded objects

 // RStreamablePtrArray<CEmbeddedObject> myArray;

 // CleanupClosePushL(myArray);

 // // Get an array of the embedded objects within the current container in the file

 // c->GetEmbeddedObjectsL(myArray);

 // // If necessary we can get a "mangled" version of the URI that 

 // // references the particular object within the file

 // // ie. "C:\file.dcf\\OBJECT1"

 // TPtrC aURI = *myArray[0];

 // // Now we can use our TPtrC later to create a TVirtualPath object from a URI

 // TVirtualPathPtr aPtr = aURI;

 // // print the file URI  "C:\file.dcf"

 // printf(aPtr.URI());

 // // print the content object's UniqueId "OBJECT1"

 // printf(aPtr.UniqueId());

 // // Create a copy of aVirtualPath on the heap so we don't have any ownership problems

 // CVirtualPath *myVirtualpath = CVirtualPath::NewL(aPtr);

 // // Can now delete the CContent object without loosing our VirtualPath

 // CleanupStack::PopAndDestroy(2);	// c, myArray

 // <hr>

 // <b><code>KNullDesC16() -  ""</code></b>

 // A zero length \c UniqueId is used to refer to the entire file. If a file is opened this way no translation of the contents will be

 // performed. The ability to open the file with no translation is required for example to attach the file to an outgoing message.

 // As with any other function in CAF access to the file is at the agents discretion.

 // <b><code>KDefaultContentObject() - "DEFAULT"</code></b>

 // Allows an application to refer to the default content object within a file. In the case of an unprotected file handled

 // by the \c F32Agent this will be the entire file, the same as if the <code>UniqueId ""</code> was used. Other agents, particularly those

 // with a single content object embedded within the file, use <code>"DEFAULT"</code> to refer to their only content object.

 // Even though the DEFAULT content object is supported, it is recommended that agents always use \c CContent to enumerate the 

 // objects within the file.

 // <hr>

 // 

 //

 /**

  @page FileOverview Files containing multiple content objects 

  - @ref FileOverviewDescription

  - @ref VirtualPaths

  - @ref VirtualPathObjects

  - @ref SpecialUniqueIds

  @section FileOverviewDescription Structure of a file containing multiple content objects

  related to a content object, see @ref ContentAttributes "Content Object Attributes".

  @image html "multiple DRM file2.gif"

  @section VirtualPaths Identifying a content object within a File

  @li \c URI      - The location of the file

  @li \c UniqueId - The content object inside the file.

  @section VirtualPathObjects Objects used to identify a content object within a File

  @code

  @endcode

  @section SpecialUniqueIds Special Cases for the UniqueId field

 */