// 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:
// <hr>
// The Content Access Framework provides a common interface for applications to access content.
// In effect it behaves as a switch between different agents, known as Content Access Agents.
// Each agent is an ECOM plugin, which implements the Content Access Agent interface <code>0x10204740</code>. 
// This interface should be a static function that creates and returns an instance of a class derived 
// from <code>ContentAccess::CAgentFactory</code> (e.g. <code>ContentAccess::CF32AgentFactory</code>).
// <code>static CAgentFactory* AgentImplementationFunction();</code>
// for reading unprotected content files. If no other agent recognizes a file the F32 agent will be used
// to read it. In effect, this is the same as opening the file using an <code>RFile</code>, but allows the application
// to use the same code to read protected and unprotected content.
// The following diagram illustrates the implementation of CAF with two fictitious agents (OMA and MPEG).
// <hr>
// The problem with this implementation is that all three agents are loaded into the application's process space,
// which represents a security risk. The application could potentially access the key used to decrypt protected
// content.
// A better solution is to implement the parts of the agent that require access to encryption/decryption keys or
// rights in a separate server process. When platform security is enabled the server implementation also allows 
// the APIs to be policed by the agent server DLL to ensure only applcations with the right capabilities will 
// have access to the content.
// To improve performance any functionality that does not require access to keys or rights should be implemented
// in the client side DLL. Client side functionality reduces the number of context switches the processor needs 
// to perform resulting in improved performance from the agent.
// There is no need to implement the F32 agent in a server process since it is only used to access unprotected content.
// <hr>
// The following guidelines are suggested for implementing Client/Server agents, but may not be appropriate
// for all agents.
// <b> Client Side Functionality </b>
// - Implement the Content Access Agent ECOM interface
// - Browse the contents of files
// - Retrieve attributes or meta-data from a file
// - All functions requiring the agent to display a user interface or dialog
// - File recognition (for client applications and Apparc MIME types)
// - Marshall calls to the server side
// <b> Server Side Functionality </b>
// - Content Encryption (protecting plaintext)
// - Content Decryption (reading DRM content)
// - Manage, protect and store Rights
// - Any potentially destructive operation such as deleting content or rights
// - Notifications
// - Capability Enforcement
// <hr>
// The APIs provided in this document indicate the functions that are likely to require a client
// process to have DRM capability in order to use the functionality. The client process will only 
// need DRM capability if it attempts to read DRM content using an CAF agent that implements a DRM
// protection scheme. 
// The capability can only be enforced by the CAF agent running in a separate server process, so it is the responsibility
// of the agent to ensure the client process has the required capabilities.
// <b>There are no capabilities required to use unprotected content.</b>
// <hr>
// CAF is used to read unprotected or DRM protected content. It is a client side DLL that must be linked with
// the process using CAF. 
// The agents may run in separate processes and will not have the correct capabilities to open files in TCB or 
// server private directories using just a file name. These files must be opened by the process that owns the 
// file and an open \c RFile handle passed to CAF in order to read them.
// <hr>
// 
//

/**
 @page CAFArchitecture Architecture
 - @ref ArchOverview
 - @ref CAFClientServer
 - @ref ClientServerImplementation 
 - @ref CAFCapability
 - @ref UsingCAF
 @section ArchOverview Overview
 There is a special agent supplied by Symbian known as the @ref AboutF32Agent "F32Agent". This agent is used as a fallback 
 @image html Architecture1.gif
 @section CAFClientServer Client / Server Agents
 @image html Architecture2.gif
 @section ClientServerImplementation Client / Server implementation guidelines
 @section CAFCapability DRM Capability
 @section UsingCAF Using CAF to read from other server private directories
*/
