berdecoder.java

java1.6众多例子参考

/*
 * @(#)file      BerDecoder.java
 * @(#)author    Sun Microsystems, Inc.
 * @(#)version   4.21
 * @(#)date      08/07/21
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 */


package com.sun.jmx.snmp;




/**
 * The <CODE>BerDecoder</CODE> class is used for decoding 
 * BER-encoded data.
 *
 * A <CODE>BerDecoder</CODE> needs to be set up with the byte string containing
 * the encoding. It maintains a current position in the byte string.
 *
 * Methods allows to fetch integer, string, OID, etc., from the current
 * position. After a fetch the current position is moved forward.
 *
 * A fetch throws a <CODE>BerException</CODE> if the encoding is not of the
 * expected type.
 *
 * <p><b>This API is a Sun Microsystems internal API  and is subject 
 * to change without notice.</b></p>
 * @version     4.21     11/17/05
 * @author      Sun Microsystems, Inc
 *
 * @since 1.5
 */

public class BerDecoder {

  /**
  * Constructs a new decoder and attaches it to the specified byte string.
  * 
  * @param b The byte string containing the encoded data.
  */

  public BerDecoder(byte b[]) {
    bytes = b ;
    reset() ;
  }

  public void reset() {
    next = 0 ;
    stackTop = 0 ;
  }

  /**
  * Fetch an integer.
  * 
  * @return The decoded integer.
  *
  * @exception BerException Current position does not point to an integer.
  */

  public int fetchInteger() throws BerException {
    return fetchInteger(IntegerTag) ;
  }


  /**
  * Fetch an integer with the specified tag.
  * 
  * @param tag The expected tag.
  *
  * @return The decoded integer.
  *
  * @exception BerException Current position does not point to an integer
  *                         or the tag is not the expected one.
  */

  public int fetchInteger(int tag) throws BerException {
    int result = 0 ;
    final int backup = next ;
    try {
      if (fetchTag() != tag) {
        throw new BerException() ;
      }
      result = fetchIntegerValue() ;
    }
    catch(BerException e) {
      next = backup ;
      throw e ;
    }
    
    return result ;
  }



  /**
  * Fetch an integer and return a long value.
  * 
  * @return The decoded integer.
  *
  * @exception BerException Current position does not point to an integer.
  */

  public long fetchIntegerAsLong() throws BerException {
    return fetchIntegerAsLong(IntegerTag) ;
  }


  /**
  * Fetch an integer with the specified tag and return a long value.
  * 
  * @param tag The expected tag.
  *
  * @return The decoded integer.
  *
  * @exception BerException Current position does not point to an integer
  *                         or the tag is not the expected one.
  */

  public long fetchIntegerAsLong(int tag) throws BerException {
    long result = 0 ;
    final int backup = next ;
    try {
      if (fetchTag() != tag) {
        throw new BerException() ;
      }
      result = fetchIntegerValueAsLong() ;
    }
    catch(BerException e) {
      next = backup ;
      throw e ;
    }
    
    return result ;
  }



  /**
  * Fetch an octet string.
  * 
  * @return The decoded string.
  *
  * @exception BerException Current position does not point to an octet string.
  */

  public byte[] fetchOctetString() throws BerException {
    return fetchOctetString(OctetStringTag) ;
  }
  

  /**
  * Fetch an octet string with a specified tag.
  * 
  * @param tag The expected tag.
  *
  * @return The decoded string.
  *
  * @exception BerException Current position does not point to an octet string
  *                         or the tag is not the expected one.
  */

  public byte[] fetchOctetString(int tag) throws BerException {
    byte[] result = null ;
    final int backup = next ;
    try {
      if (fetchTag() != tag) {
        throw new BerException() ;
      }
      result = fetchStringValue() ;
    }
    catch(BerException e) {
      next = backup ;
      throw e ;
    }
    
    return result ;
  }


  /**
  * Fetch an object identifier.
  * 
  * @return The decoded object identifier as an array of long.
  */

  public long[] fetchOid() throws BerException {
    return fetchOid(OidTag) ;
  }
  

  /**
  * Fetch an object identifier with a specified tag.
  * 
  * @param tag The expected tag.
  *
  * @return The decoded object identifier as an array of long.
  *
  * @exception BerException Current position does not point to an oid
  *                         or the tag is not the expected one.
  */

  public long[] fetchOid(int tag) throws BerException {
    long[] result = null ;
    final int backup = next ;
    try {
      if (fetchTag() != tag) {
        throw new BerException() ;
      }
      result = fetchOidValue() ;
    }
    catch(BerException e) {
      next = backup ;
      throw e ;
    }
    
    return result ;
  }


  /**
  * Fetch a <CODE>NULL</CODE> value.
  *
  * @exception BerException Current position does not point to <CODE>NULL</CODE> value.
  */

  public void fetchNull() throws BerException {
    fetchNull(NullTag) ;
  }


  /**
  * Fetch a <CODE>NULL</CODE> value with a specified tag.
  * 
  * @param tag The expected tag.
  *
  * @exception BerException Current position does not point to 
  *            <CODE>NULL</CODE> value or the tag is not the expected one.
  */

  public void fetchNull(int tag) throws BerException {
    final int backup = next ;
    try {
      if (fetchTag() != tag) {
        throw new BerException() ;
      }
      final int length = fetchLength();
      if (length != 0) throw new BerException();
    }
    catch(BerException e) {
      next = backup ;
      throw e ;
    }
  }
  
  

  /**
  * Fetch an <CODE>ANY</CODE> value. In fact, this method does not decode anything
  * it simply returns the next TLV as an array of bytes.
  * 
  * @return The TLV as a byte array.
  *
  * @exception BerException The next TLV is really badly encoded...
  */

  public byte[] fetchAny() throws BerException {
    byte[] result = null ;
    final int backup = next ;
    try {
      final int tag = fetchTag() ;
      final int contentLength = fetchLength() ;
      if (contentLength < 0) throw new BerException() ;
      final int tlvLength = next + contentLength - backup ;
      if (contentLength > (bytes.length - next)) 
	  throw new IndexOutOfBoundsException("Decoded length exceeds buffer");
      final byte[] data = new byte[tlvLength] ;
      java.lang.System.arraycopy(bytes,backup,data,0,tlvLength);
      // for (int i = 0 ; i < tlvLength ; i++) {
      //  data[i] = bytes[backup + i] ;
      // }
      next = next + contentLength ;
      result = data;
    }
    catch(IndexOutOfBoundsException e) {
      next = backup ;
      throw new BerException() ;
    } 
    // catch(Error e) {
    //    debug("fetchAny: Error decoding BER: " + e);
    //    throw e;
    // }
    
    return result ;
  }


  /**
  * Fetch an <CODE>ANY</CODE> value with a specific tag.
  * 
  * @param tag The expected tag.
  *
  * @return The TLV as a byte array.
  *
  * @exception BerException The next TLV is really badly encoded...
  */

  public byte[] fetchAny(int tag) throws BerException {
    if (getTag() != tag) {
      throw new BerException() ;
    }
    return fetchAny() ;
  }
  
  

  /**
  * Fetch a sequence header.
  * The decoder computes the end position of the sequence and push it
  * on its stack.
  * 
  * @exception BerException Current position does not point to a sequence header.
  */

  public void openSequence() throws BerException {
    openSequence(SequenceTag) ;
  }


  /**
  * Fetch a sequence header with a specific tag.
  * 
  * @param tag The expected tag.
  *
  * @exception BerException Current position does not point to a sequence header
  *                         or the tag is not the expected one.
  */

  public void openSequence(int tag) throws BerException {
    final int backup = next ;
    try {
      if (fetchTag() != tag) {
        throw new BerException() ;
      }
      final int l = fetchLength() ;
      if (l < 0) throw new BerException();
      if (l > (bytes.length - next)) throw new BerException();
      stackBuf[stackTop++] = next + l ;
    }
    catch(BerException e) {
      next = backup ;
      throw e ;
    }
  }


  /**
  * Close a sequence.
  * The decode pull the stack and verifies that the current position
  * matches with the calculated end of the sequence. If not it throws
  * an exception.
  * 
  * @exception BerException The sequence is not expected to finish here.
  */

  public void closeSequence() throws BerException {
    if (stackBuf[stackTop - 1] == next) {
      stackTop-- ;
    }
    else {