// 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 "Symbian Foundation License v1.0"
// which accompanies this distribution, and is available
// at the URL "http://www.symbianfoundation.org/legal/sfl-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
*/
