// 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

*/