/* ServerStore.java -- 
   Copyright (C) 2003, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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USA

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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permission to link this library with independent modules to produce an
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package gnu.javax.crypto.sasl.srp;

import java.util.HashMap;

/**
 * The server-side implementation of the SRP security context store.
 */
public class ServerStore
{
  /** The underlying singleton. */
  private static ServerStore singleton = null;
  /** The map of sid --> Security Context record. */
  private static final HashMap sid2ssc = new HashMap();
  /** The map of sid --> Session timing record. */
  private static final HashMap sid2ttl = new HashMap();
  /** A synchronisation lock. */
  private static final Object lock = new Object();
  /** A counter to generate legible SIDs. */
  private static int counter = 0;

  /** Private constructor to enforce Singleton pattern. */
  private ServerStore()
  {
    super();

    // TODO: add a cleaning timer thread
  }

  /**
   * Returns the classloader Singleton.
   * 
   * @return the classloader Singleton instance.
   */
  static synchronized final ServerStore instance()
  {
    if (singleton == null)
      singleton = new ServerStore();
    return singleton;
  }

  /**
   * Returns a legible new session identifier.
   * 
   * @return a new session identifier.
   */
  static synchronized final byte[] getNewSessionID()
  {
    final String sid = String.valueOf(++counter);
    return new StringBuffer("SID-")
        .append("0000000000".substring(0, 10 - sid.length())).append(sid)
        .toString().getBytes();
  }

  /**
   * Returns a boolean flag indicating if the designated session is still alive
   * or not.
   * 
   * @param sid the identifier of the session to check.
   * @return <code>true</code> if the designated session is still alive.
   *         <code>false</code> otherwise.
   */
  boolean isAlive(final byte[] sid)
  {
    boolean result = false;
    if (sid != null && sid.length != 0)
      {
        synchronized (lock)
          {
            final String key = new String(sid);
            final StoreEntry ctx = (StoreEntry) sid2ttl.get(key);
            if (ctx != null)
              {
                result = ctx.isAlive();
                if (! result) // invalidate it en-passant
                  {
                    sid2ssc.remove(key);
                    sid2ttl.remove(key);
                  }
              }
          }
      }
    return result;
  }

  /**
   * Records a mapping between a session identifier and the Security Context of
   * the designated SRP server mechanism instance.
   * 
   * @param ttl the session's Time-To-Live indicator (in seconds).
   * @param ctx the server's security context.
   */
  void cacheSession(final int ttl, final SecurityContext ctx)
  {
    synchronized (lock)
      {
        final String key = new String(ctx.getSID());
        sid2ssc.put(key, ctx);
        sid2ttl.put(key, new StoreEntry(ttl));
      }
  }

  /**
   * Updates the mapping between the designated session identifier and the
   * designated server's SASL Security Context. In the process, computes and
   * return the underlying mechanism server's evidence that shall be returned to
   * the client in a session re-use exchange.
   * 
   * @param sid the identifier of the session to restore.
   * @return an SRP server's security context.
   */
  SecurityContext restoreSession(final byte[] sid)
  {
    final String key = new String(sid);
    final SecurityContext result;
    synchronized (lock)
      {
        result = (SecurityContext) sid2ssc.remove(key);
        sid2ttl.remove(key);
      }
    return result;
  }

  /**
   * Removes all information related to the designated session ID.
   * 
   * @param sid the identifier of the seesion to invalidate.
   */
  void invalidateSession(final byte[] sid)
  {
    final String key = new String(sid);
    synchronized (lock)
      {
        sid2ssc.remove(key);
        sid2ttl.remove(key);
      }
  }
}