icmpheader.java

来自「This a java ICMP JNI interface」· Java 代码 · 共 566 行 · 第 1/2 页

     * decoded.
     * </P>
     * 
     * <P>
     * If there is an insufficent amount of data to decode a header then an
     * exception is thrown.
     * </P>
     * 
     * @param data
     *            The data buffer containing the header
     * @param offset
     *            The offset of the header in the buffer
     * 
     * @exception java.lang.IndexOutOfBoundsException
     *                Thrown if there is not enough data to construct the
     *                header.
     * 
     */
    public ICMPHeader(byte[] data, int offset) {
        if ((data.length - offset) < getNetworkSize())
            throw new IndexOutOfBoundsException("Insufficient number of bytes available to construct the ICMP header");

        m_type = data[offset++];
        m_code = data[offset++];
        m_checksum = (short) (byteToShort(data[offset++]) << 8 | byteToShort(data[offset++]));
        m_sequence = (short) (byteToShort(data[offset++]) << 8 | byteToShort(data[offset++]));
        m_ident = (short) (byteToShort(data[offset++]) << 8 | byteToShort(data[offset++]));
    }

    /**
     * Returns the 8-bit type code for the ICMP packet.
     * 
     * @return The ICMP type.
     */
    public final byte getType() {
        return m_type;
    }

    /**
     * Sets the 8-bit type code for the packet.
     * 
     * @param type
     *            The new ICMP type.
     * 
     */
    protected void setType(byte type) {
        m_type = type;
    }

    /**
     * Returns the 8-bit code for the ICMP packet.
     * 
     * @return The ICMP code.
     * 
     */
    public final byte getCode() {
        return m_code;
    }

    /**
     * Sets the 8-bit code for the ICMP packet
     * 
     * @param code
     *            The new ICMP code.
     * 
     */
    public final void setCode(byte code) {
        m_code = code;
    }

    /**
     * Returns the sequence identifier for the ICMP header.
     * 
     * @return The 16-bit sequence identifier.
     * 
     */
    public final short getSequenceId() {
        return m_sequence;
    }

    /**
     * Gets the next global identifier and sets the value in the object. In
     * addition the new sequence identifier is returned.
     * 
     * @return The new 16-bit sequence identifier.
     * 
     */
    public final short setNextSequenceId() {
        m_sequence = nextSequenceId();
        return m_sequence;
    }

    /**
     * Sets the headers 16-bit sequence identifier.
     * 
     * @param id
     *            The new 16-bit sequence id.
     * 
     */
    public final void setSequenceId(short id) {
        m_sequence = id;
    }

    /**
     * Used to get the headers user defined identity.
     * 
     * @return The 16-bit identity.
     * 
     */
    public final short getIdentity() {
        return m_ident;
    }

    /**
     * Sets the header's 16-bit user defined identity value.
     * 
     * @param identity
     *            The header's new identity.
     * 
     */
    public final void setIdentity(short identity) {
        m_ident = identity;
    }

    /**
     * Used to retrieve the current checksum for the header. This is the last
     * checksum computed for the header (or it's derived classes). To compute
     * the new checksum a call to the method computeChecksum() must be called.
     * 
     * @return The 16-bit one's compliment checksum.
     * 
     */
    public final short getChecksum() {
        return m_checksum;
    }

    protected void setChecksum(short sum) {
        m_checksum = sum;
    }

    /**
     * Provides the default checksum implementation for the ICMP header. It MUST
     * be overriden by any derived classes to ensure that the checksum includes
     * the dervived class data. Once the checksum is calculated, a call to the
     * method getChecksum() will return the calculated sum.
     */
    public void computeChecksum() {
        OC16ChecksumProducer summer = new OC16ChecksumProducer();
        computeChecksum(summer);
        m_checksum = summer.getChecksum();
    }

    /**
     * Used by derived classes to begin the checksum process. The process
     * involves setting the checksum to zero and then performing the checksum
     * over the various values.
     * 
     * @param summer
     *            The checksum builder object.
     */
    protected void computeChecksum(OC16ChecksumProducer summer) {
        summer.reset();
        summer.add(m_type, m_code);

        // adding zero has should no effect....
        // m_checksum = 0;
        summer.add((short) 0);

        summer.add(m_sequence);
        summer.add(m_ident);
    }

    /**
     * Writes the ICMP header out to the specified buffer at the starting
     * offset. If the buffer does not have sufficent data to store the
     * information then an IndexOutOfBoundsException is thrown.
     * 
     * @param buf
     *            The storage buffer.
     * @param offset
     *            The location to start in buf.
     * 
     * @return The new offset after storing to the buffer.
     * 
     * @exception IndexOutOfBoundsException
     *                Thrown if the buffer does not have enough storage space.
     * 
     */
    protected int storeToBuffer(byte[] buf, int offset) {
        if (buf.length < (offset + 8))
            throw new IndexOutOfBoundsException("Array index overflow in buffer");

        buf[offset++] = (byte) (m_type);
        buf[offset++] = (byte) (m_code);
        buf[offset++] = (byte) ((m_checksum >>> 8) & 0xff);
        buf[offset++] = (byte) (m_checksum & 0xff);
        buf[offset++] = (byte) ((m_ident >>> 8) & 0xff);
        buf[offset++] = (byte) (m_ident & 0xff);
        buf[offset++] = (byte) ((m_sequence >>> 8) & 0xff);
        buf[offset++] = (byte) (m_sequence & 0xff);

        return offset;
    }

    /**
     * Reads the ICMP header from the specified buffer and sets the internal
     * fields equal to the data. If the buffer does not have sufficent data to
     * restore the header then an IndexOutOfBoundsExceptoin is thrown by the
     * method.
     * 
     * @param buf
     *            The buffer to read the data from.
     * @param offset
     *            The offset to start reading data.
     * 
     * @return The new offset after reading the data.
     * 
     * @exception IndexOutOfBoundsException
     *                is thrown if there is not sufficent data in the buffer.
     * 
     */
    protected int loadFromBuffer(byte[] buf, int offset) {
        if (buf.length < (offset + 8))
            throw new IndexOutOfBoundsException("Insufficient data to load ICMP header");

        m_type = (byte) (buf[offset++]);
        m_code = (byte) (buf[offset++]);
        m_checksum = (short) (byteToShort(buf[offset++]) << 8 | byteToShort(buf[offset++]));

        m_ident = (short) (byteToShort(buf[offset++]) << 8 | byteToShort(buf[offset++]));

        m_sequence = (short) (byteToShort(buf[offset++]) << 8 | byteToShort(buf[offset++]));

        return offset;
    }

    /**
     * Returns the number of bytes required to read/write an icmp header. A
     * header is composed of a fixed size number of byte. This is not expected
     * to change, but this method allows derived classes to query the number of
     * bytes for reading/writing an icmp header. Thus should the standard ever
     * change, the derived class should be able to dynamically handle the
     * change.
     * 
     * @return The number of bytes required to read/write an icmp header.
     * 
     */
    public static int getNetworkSize() {
        return 8;
    }

    /**
     * Used to test to see if the header is an echo reply message. If it is an
     * echo reply message then true is returned.
     * 
     * @return True if the header marks an echo reply.
     * 
     */
    public final boolean isEchoReply() {
        return (m_type == TYPE_ECHO_REPLY);
    }

    /**
     * Used to test to see if the header is an echo request message. If it is an
     * echo request message then true is returned.
     * 
     * @return True if the header marks an echo request.
     * 
     */
    public final boolean isEchoRequest() {
        return (m_type == TYPE_ECHO_REQUEST);
    }

    /**
     * Converts the object to a string of bytes.
     */
    public byte[] toBytes() {
        byte[] b = new byte[8];
        storeToBuffer(b, 0);
        return b;
    }
}