message.java

用于传感器网络的节点操作系统 TinyOS 结构设计非常有意思

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 * Authors:  David Gay  <[e-mail]>
 *           Intel Research Berkeley Lab
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/**
 * Message class (encode/decode tinyos messages).<p>
 *
 * The base class for encoding and decoding tinyos messages.  Provides
 * methods to read and write bit fields at an offset for a particular bit
 * length.  Intended for use by the Java code generated by mig.
 *
 * @version	1, 15 Jul 2002
 * @author	David Gay
 */
package net.tinyos.message;

public class Message implements Cloneable {

    /**
     * The maximum number of characters read from an 8-bit array field
     * being converted into a Java String.
     */
    public static final int MAX_CONVERTED_STRING_LENGTH = 512;

    /** 
     * The underlying byte array storing the data for this message. 
     * This is private to enforce access to the data through the accessor
     * methods in this class, which do bounds checking and manage the
     * base_offset for embedded messages.
     */
    private byte[] data;

    /** 
     * The base offset into the data. This allows the message data to
     * exist at some non-zero offset into the actual data.
     */
    protected int base_offset;

    /**
     * The actual length of the message data. Must be less than or
     * equal to (data.length - base_offset).
     */
    protected int data_length;

    /** Private to prevent no-arg instantiation. */
    private Message() {
    }

    /**
     * Construct a new message of the given size.
     * @param data_length The size of the message to create.
     */
    protected Message(int data_length) {
      this(new byte[data_length]);
    }

    /**
     * Construct a new message of the given size and base offset.
     * Allocates a new byte array of size data_length+base_offset.
     * @param data_length The size of the message to create.
     * @param base_offset The base offset into the newly created message.
     */
    protected Message(int data_length, int base_offset) {
      this(new byte[data_length+base_offset], base_offset);
    }

    /**
     * Construct a message using data as the storage.
     * The length of data determines the length of this message.
     * @param data the storage for this message
     */
    protected Message(byte[] data) {
	this.data = data;
	this.base_offset = 0;
	this.data_length = data.length;
    }

    /**
     * Construct a message using data as the storage.
     * Use the given base_offset as the base offset into the 
     * data array. The data length will be (data.length - base_offset).
     * @param data the storage for this message
     * @param base_offset the base offset into the data array
     */
    protected Message(byte[] data, int base_offset) {
	this.data = data;
	this.base_offset = base_offset;
	this.data_length = data.length - base_offset;
    }

    /**
     * Construct a message using data as the storage.
     * Use the given base_offset as the base offset into the 
     * data array, and the specified data length.
     * @param data the storage for this message
     * @param base_offset the base offset into the data array
     * @param data_length the length of the message data
     */
    protected Message(byte[] data, int base_offset, int data_length) {
	this.data = data;
	this.base_offset = base_offset;
	this.data_length = data_length;
	if (base_offset + data_length > data.length) throw new ArrayIndexOutOfBoundsException("Cannot create Message with base_offset "+base_offset+", data_length "+data_length+" and data array size "+data.length);
    }

    /**
     * Construct an embedded message within the given 'msg'.
     * Use the given base_offset as the base offset into the 
     * data array, and the specified data length.
     * @param msg the message to embed this message into
     * @param base_offset the base offset into the data array
     * @param data_length the length of the message data
     */
    protected Message(Message msg, int base_offset, int data_length) {
      this(msg.dataGet(), msg.base_offset+base_offset, data_length);
    }

    private Message cloneself() {
	Message copy;

	try {
	    copy = (Message)super.clone();
	}
	catch (CloneNotSupportedException e) {
	    System.err.println("Message: WARNING: CloneNotSupportedException in cloneself(): "+e);
	    System.err.println("Message: This is a bug - please contact [e-mail]");
	    copy = null;
	    System.exit(2);
	}
	return copy;
    }

    /**
     * Clone this Message, including making a copy of its data
     */
    public Object clone() {
	Message copy = cloneself();
	copy.data = (byte[])data.clone();
	copy.base_offset = this.base_offset;
	copy.data_length = this.data_length;
	return copy;
    }

    /**
     * Clone this Message, but give it a new unitialised data array of size
     * size
     * @param size size of the new data array
     */
    public Message clone(int size) {
	Message copy = cloneself();
	copy.data = new byte[size];
	copy.base_offset = this.base_offset;
	copy.data_length = size;
	return copy;
    }

    /**
     * Copy new data for this message from 'data'. 
     * Copies min(data.length, this.data_length) bytes.
     * @param data the array containing the data to be copied
     * @exception ArrayIndexOutOfBoundsException if any of
     * data[0..getData().length - 1] are invalid
     */
    public void dataSet(byte[] data) {
	dataSet(data, 0, this.base_offset, Math.min(this.data_length, data.length));
    }

    /**
     * Copy new data for this message from offsetFrom in data to
     * offsetTo in this message. Copies a total of length bytes
     * @param data the array containing the data to be copied
     * @param offsetFrom the offset in data to start copying from
     * @param offsetTo the offset at which to start copying data into
     * this message.
     * @param length bytes are copied.
     * @exception ArrayIndexOutOfBoundsException if any of
     * the source or target indices are invalid
     */
    public void dataSet(byte[] data, int offsetFrom, int offsetTo, int length) {
      System.arraycopy(data, offsetFrom, this.data, offsetTo+base_offset, length);
    }

    /**
     * Return the raw byte array representing the data of this message.
     * Note that only indices in the range
     * (this.baseOffset(), this.baseOffset()+this.dataLength()) are
     * valid. 
     */
    public byte[] dataGet() {
	return data;
    }

    /**
     * Return the base offset into the data array for this message.
     */
    public int baseOffset() {
        return base_offset;
    }

    /**
     * Return the length of the data (in bytes) contained in this message.
     */
    public int dataLength() {
        return data_length;
    }

    /**
     * Return the active message type of this message (-1 if unknown)
     */
    public int amType() {
	return -1;
    }

    // ASSUMES: little endian bits & bytes

    // Check that length bits from offset are in bounds
    private void checkBounds(int offset, int length) {
	if (offset < 0 || length <= 0 || offset + length > (data_length * 8))
	    throw new ArrayIndexOutOfBoundsException("Message.checkBounds: bad offset ("+offset+") or length ("+length+"), for data_length "+data_length);
    }

    // Check that value is valid for a bitfield of length length
    private void checkValue(int length, long value) {
	if (length != 64 && (value < 0 || value >= 1L << length))
	    throw new IllegalArgumentException("Message.checkValue: bad length ("+length+" or value ("+value+")");
    }

    // Unsigned byte read
    private int ubyte(int offset) {
	int val = data[base_offset+offset];

	if (val < 0) return val + 256;
	else return val;
    }

    /**
     * Read the length bit unsigned int at offset
     * @param offset bit offset where the unsigned int starts
     * @param length bit length of the unsigned int
     * @exception ArrayIndexOutOfBoundsException for invalid offset, length
     */
    protected long getUIntElement(int offset, int length) {
	checkBounds(offset, length);

	int byteOffset = offset >> 3;
	int bitOffset = offset & 7;
	int shift = 0;
	long val = 0;

	// all in one byte case
	if (length + bitOffset <= 8)
	    return (ubyte(byteOffset) >> bitOffset) & ((1 << length) - 1);

	// get some high order bits
	if (bitOffset > 0) {
	    val = ubyte(byteOffset) >> bitOffset;
	    byteOffset++;
	    shift += 8 - bitOffset;
	    length -= 8 - bitOffset;
	}

	while (length >= 8) {
	    val |= (long)ubyte(byteOffset++) << shift;
	    shift += 8;
	    length -= 8;
	}

	// data from last byte
	if (length > 0)
	    val |= (long)(ubyte(byteOffset) & ((1 << length) - 1)) << shift;

	return val;
    }

    /**
     * Set the length bit unsigned int at offset to val
     * @param offset bit offset where the unsigned int starts
     * @param length bit length of the unsigned int
     * @param val value to set the bit field to
     * @exception ArrayIndexOutOfBoundsException for invalid offset, length
     * @exception IllegalArgumentException if val is an out-of-range value
     * for this bitfield
     */
    protected void setUIntElement(int offset, int length, long val) {
	checkBounds(offset, length);
	//checkValue(length, val);

	int byteOffset = offset >> 3;
	int bitOffset = offset & 7;
	int shift = 0;

	// all in one byte case
	if (length + bitOffset <= 8) {
	    data[base_offset+byteOffset] = (byte)
		((ubyte(byteOffset) & ~(((1 << length) - 1) << bitOffset))
		 | val << bitOffset);
	    return;
	}

	// set some high order bits
	if (bitOffset > 0) {
	    data[base_offset+byteOffset] = (byte)
		((ubyte(byteOffset) & ((1 << bitOffset) - 1)) | val << bitOffset);
	    byteOffset++;
	    shift += 8 - bitOffset;
	    length -= 8 - bitOffset;
	}

	while (length >= 8) {
	    data[base_offset+(byteOffset++)] = (byte)(val >> shift);
	    shift += 8;
	    length -= 8;
	}

	// data for last byte
	if (length > 0)
	    data[base_offset+byteOffset] = (byte)
		((ubyte(byteOffset) & ~((1 << length) - 1)) | val >> shift);
    }

    /**
     * Read the length bit signed int at offset
     * @param offset bit offset where the signed int starts
     * @param length bit length of the signed int
     * @exception ArrayIndexOutOfBoundsException for invalid offset, length
     */
    protected long getSIntElement(int offset, int length)
	throws ArrayIndexOutOfBoundsException {
	long val = getUIntElement(offset, length);

	if (length == 64)
	    return val;

	if ((val & 1L << (length - 1)) != 0)
	    return val - (1L << length);

	return val;
    }

    /**
     * Set the length bit signed int at offset to val
     * @param offset bit offset where the signed int starts
     * @param length bit length of the signed int
     * @param val value to set the bit field to
     * @exception ArrayIndexOutOfBoundsException for invalid offset, length
     * @exception IllegalArgumentException if val is an out-of-range value
     * for this bitfield
     */ 
   protected void setSIntElement(int offset, int length, long value)
	throws ArrayIndexOutOfBoundsException {
	if (length != 64 && value >= 1L << (length - 1))
	    throw new IllegalArgumentException();

	if (length != 64 && value < 0)
	    value += 1L << length;

	setUIntElement(offset, length, value);
    }

    /**
     * Read the 32 bit IEEE float at offset
     * @param offset bit offset where the float starts
     * @param length is ignored
     * @exception ArrayIndexOutOfBoundsException for invalid offset
     */
    protected float getFloatElement(int offset, int length)
	throws ArrayIndexOutOfBoundsException {

	return Float.intBitsToFloat((int)getUIntElement(offset, 32));
    }

    /**
     * Set the 32 bit IEEE float at offset to value
     * @param offset bit offset where the float starts
     * @param length is ignored
     * @parem value value to store in bitfield
     * @exception ArrayIndexOutOfBoundsException for invalid offset
     */
    protected void setFloatElement(int offset, int length, float value)
	throws ArrayIndexOutOfBoundsException {

	// using SInt because floatToRawIntBits might return a negative value
	setSIntElement(offset, 32, Float.floatToRawIntBits(value));
    }
}