DEROid.java

/*
 * Copyright (C) 2006-2008 Alfresco Software Limited.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 * As a special exception to the terms and conditions of version 2.0 of 
 * the GPL, you may redistribute this Program in connection with Free/Libre 
 * and Open Source Software ("FLOSS") applications as described in Alfresco's 
 * FLOSS exception.  You should have recieved a copy of the text describing 
 * the FLOSS exception, and it is also available here: 
 * http://www.alfresco.com/legal/licensing"
 */

package org.alfresco.jlan.server.auth.asn;

import java.io.IOException;
import java.util.StringTokenizer;

/**
 * DER Object Identifier Class
 * 
 *
 * @author gkspencer
 */
public class DEROid extends DERObject {

  // Object identifier string
  
  private String m_oid;
  
  /**
   * Default constructor
   */
  public DEROid() {
  }
  
  /**
   * Class constructor
   * 
   * @param oid String
   */
  public DEROid(String oid) {
    m_oid = oid;
  }
  
  /**
   * Return the object identifier string
   * 
   * @return String
   */
  public final String getOid() {
    return m_oid;
  }
  
  /**
   * DER encode the object
   * 
   * @param buf DERBuffer
   */
  public void derDecode(DERBuffer buf)
    throws IOException {
    
    // Make sure the object type is an Oid
    
    if ( buf.unpackType() == DER.ObjectIdentifier) {
      
      // Get the Oid length
      
      int len = buf.unpackLength();
      
      long oidVal = 0L;
      StringBuffer oidStr = new StringBuffer();
      
      for (int i = 0; i < len; i++) {
        
        // Get a byte from the Oid data, and add the bottom 7 bits to the current value
        
        int byt = buf.unpackByte();

        oidVal = (oidVal << 7) + (byt & 0x7F);

        // Check if this is the last byte for the current value
        
        if ((byt & 0x80) == 0) {
          
          // Add the prefix for the first value
          
          if ( oidStr.length() == 0) {
            switch ((int) (oidVal/40)) {
              case 0:
                oidStr.append("0");
                break;
              case 1:
                oidStr.append("1");
                oidVal -= 40;
                break;
              default:
                oidStr.append("2");
                oidVal -= 80;
                break;
            }
          }
            
          // Append the current value
            
          oidStr.append(".");
          oidStr.append( Long.toString(oidVal));
            
          // Reset the current Oid value
            
          oidVal = 0L;
        }
      }

      // Set the Oid string
      
      m_oid = oidStr.toString();
    }
    else
      throw new IOException("Invalid type in buffer, not ObjectIdentifier");
  }
  
  /**
   * DER encode the object
   * 
   * @param buf DERBuffer
   */
  public void derEncode( DERBuffer buf)
    throws IOException {
    
    // Pack the data type and skip the length, save the buffer position for the length
    
    buf.packByte( DER.ObjectIdentifier);
    
    int lenPos = buf.getPosition();
    buf.packByte( 0);
    
    // Split the OID into seperate fields and encode
    
    StringTokenizer tok = new StringTokenizer( m_oid, ".");
    
    packOidField( buf, (Integer.parseInt(tok.nextToken()) * 40) + Integer.parseInt(tok.nextToken()));
    
    while ( tok.hasMoreTokens()) {
      packOidField( buf, Integer.parseInt(tok.nextToken()));
    }
    
    // Pack the length
    
    int len = buf.getPosition() - (lenPos + 1);
    buf.packByteAt( lenPos, len);
  }
  
  /**
   * Pack an OID field value in ASN.1 format
   * 
   * @param buf DERBuffer
   * @param oidVal long
   * @throws IOException
   */
  private void packOidField( DERBuffer buf, long oidVal)
    throws IOException
  {
    int fieldShift = 56;
    
    while ( fieldShift > 0) {
      if ( oidVal > (1L << fieldShift))
        buf.packByte((int) ( oidVal >> fieldShift) | 0x80);
      fieldShift -= 7;
    }
    buf.packByte((int) ( oidVal & 0x7F));
  }
  
  /**
   * Return the OID as a string
   * 
   * @return String
   */
  public String toString() {
    StringBuffer str = new StringBuffer();
    
    str.append("[Oid:");
    str.append(m_oid);
    str.append("]");
    
    return str.toString();
  }
}