// Copyright (c) 2004-2009 Nokia Corporation and/or its subsidiary(-ies).

// All rights reserved.

// This component and the accompanying materials are made available

// under the terms of "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:

// cache.h - the record cache

//

#ifndef __CACHE_H__

#define __CACHE_H__

/**

@file cache.h

DNS cache

@internalComponent	Domain Name Resolver

*/

#include "record.h"		// ...for TDndRecordLRU (and indirectly class, type symbols and TInetAddr)

const TInt KDndMaxRecords = 100;	//< Maximum mumber of records allowed in the cache.

class CDndNameSpace;

class CDndEngine;

/**

// The cache maintains a collection of (question, answer) pairs.

//

// The question (= the search key for the cache) has the

// following components:

//

// @li namespace id

// @li domain-name (dotted notation)

// @li DNS query type (EDnsQType)

// @li DNS query class (EDnsQClass)

//

// The answer is contained within CDndRecord class. Among other

// things, it contains the full original reply from some DNS server

// for the question.

//

// The cache is implemented as a forest of trees, one tree

// for each name space. Each component of the domain-name

// becomes a node in the tree. A node at any non-leaf level can have

// zero or more answers attached (for. example, the domain name "nokia.fi"

// can have both "A" (address) and "NS" (name server) answers

// associated it.

//

// The leaf nodes must have at least one answer. When

// the last answer is expired or otherwise removed from a leaf node,

// the node itself is also removed. A tree containing no answers

// consists just of the root node (name space node).

//

// For example, if in the below example, the "A" answer associated with

// query (namespace=\\<global\\>, domain-name="www.nokia.com", query=A, class=IN)

// is removed, then also the nodes for "www" and "nokia" are pruned away.

@verbatim

                      cache

                  .............

              <global>          <local>

                / |              /  \

              fi com            |    |

             /    |  \         muu  foo

            /     |    \        |  /   \ 

        nokia  symbian nokia  ..A.A....AAAA... (lru)

       / |  \     |      |   .

    ..A..NS www  www    www .

           . |    |      | .

            .A....A......A

@endverbatim

// The tree implementation is not directly visible outside the cache

// implementation. The CDndCache::FindL returns only a pointer to the

// answer (CDndRecord).

//

// There is a limit to the number of answers (KDndMaxRecords) that

// can be stored. If this limit is reached, the <b>least recently used</b>

// answers are deleted, if possible. An answer cannot be deleted

// is it is currently being used (locked) by some resolver.

*/

class CDndCache : public CBase

	{

	// See implementation for methods comments!

public:

	CDndCache();

	void ConstructL();

	~CDndCache();

	TInt GetServerAddress(const TUint32 aNameSpace, TInetAddr &aAddr);

	void SetServerAddress(const TUint32 aNameSpace, const TInetAddr &aAddr, const TInt aState);

	CDndRecord *FindL(const TUint32 aNameSpace, const TDesC8 &aName, const EDnsQType aType, const EDnsQClass aClass, 

						const TTime &aReqTime);		

	void Dump(CDndEngine &aControl);

	void Flush();

private:

	CDndNameSpace *GetNameSpace(const TUint32 aNameSpace);

	// The roots of the name-spaces

	CDndNameSpace *iRootList;

	// The LRU list of cache records

	TDndRecordLRU iRecordList;

	};

#endif