/*
* Copyright © 2003 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package javax.microedition.io;
import java.io.*;
/**
* This class defines an abstract interface for datagram packets.
* The implementations of this interface hold data to be
* sent or received from a <code>DatagramConnection</code> object.
* <p>
* Since this is an interface class, the internal structure
* of the datagram packets is not defined here. However, it is
* assumed that each implementation of this interface will
* provide the following fields / state variables (the actual
* implementation and the names of these fields may vary):
* <ul>
* <li><i>buffer</i>: the internal buffer in which data is stored
* <li><i>offset</i>: the read/write offset for the internal buffer
* <li><i>length</i>: the length of the data in datagram packet
* <li><i>address</i>: the destination or source address
* <li><i>read/write pointer</i>: a pointer that is added to the
* <i>offset</i> to point to the current data location during a
* read or write operation
* </ul>
* <p>
* <strong>Reading and Writing</strong>
* <p>
* The <code>Datagram</code> interface extends interfaces
* <code>DataInput</code> and <code>DataOutput</code> in order
* to provide a simple way to read and write binary data in and out of
* the datagram buffer instead of using <code>getData</code> and
* <code>setData</code> methods. Writing automatically increments
* <i>length</i> and reading will continue while the <i>read/write pointer</i>
* is less than <i>length</i>. Before any writing is done reset must be called.
* If <code>setData()</code> is to be used when reading or writing, any value
* for the <code>offset</code> parameter other than 0 is not supported.
* <p>
* For example to write to datagram:
* <pre>
* datagram = connection.newDatagram(max);
*
* // Reset prepares the datagram for writing new message.
* datagram.reset();
*
* // writeUTF automatically increases the datagram length.
* datagram.writeUTF("hello world");
*
* connection.send(datagram);
* </pre>
* For example to read from a datagram (single use only):
* <pre>
* datagram = connection.newDatagram(max);
*
* connection.receive(datagram);
*
* message = datagram.readUTF();
* </pre>
* <strong>Reusing Datagrams</strong>
* <p>
* It should be noted the <i>length</i> above is returned
* from <code>getLength</code> and can have different meanings at different
* times. When sending <i>length</i> is the number of bytes to send. Before
* receiving <i>length</i> is the maximum number of bytes to receive.
* After receiving <i>length</i> is the number of bytes that were received.
* So when reusing a datagram to receive after sending or receiving, length
* must be set back to the maximum using <code>setLength</code>.
* <pre>
* datagram = connection.newDatagram(max);
*
* while (notDone) {
*
* // The last receive in the loop changed the length
* // so put it back to the maximum length.
* datagram.setLength(max);
* connection.receive(datagram);
*
* data = datagram.getData();
* bytesReceived = datagram.getLength();
*
* // process datagram ...
* }
* </pre>
* When reading instead of using <code>getData</code> the <code>reset</code>
* method must be used.
* <pre>
* datagram = connection.newDatagram(max);
*
* while (notDone) {
*
* // The last read in the loop changed the read pointer
* // so reset the pointer.
* datagram.reset();
* datagram.setLength(max);
* connection.receive(datagram);
*
* message = datagram.readUTF(message);
*
* // process message ...
* }
* </pre>
* For example to reread a datagram:
* <pre>
* connection.receive(datagram);
*
* message = datagram.readUTF(message);
*
* len = datagram.getLength();
*
* datagram.reset();
*
* datagram.setLength(len);
*
* copy = datagram.readUTF(message);
* </pre>
*
* @author Brian Modra, Nik Shaylor, Stephen Flores
* @version 12/17/01 (CLDC 1.1)
* @since CLDC 1.0
*/
public interface Datagram extends DataInput, DataOutput {
/**
* Get the address of the datagram.
*
* @return the address in string form, or null if no address was set
*
* @see #setAddress
*/
public String getAddress();
/**
* Get the contents of the data buffer.
* <p>
* Depending on the implementation, this operation may return
* the internal buffer or a copy of it. However, the user
* must not assume that the contents of the internal data
* buffer can be manipulated by modifying the data returned by
* this operation. Rather, the <code>setData</code> operation
* should be used for changing the contents of the internal
* buffer.
*
* @return the data buffer as a byte array
*
* @see #setData
*/
public byte[] getData();
/**
* Get the length of the datagram.
*
* @return the length state variable
*
* @see #setLength
*/
public int getLength();
/**
* Get the offset.
*
* @return the offset state variable
*/
public int getOffset();
/**
* Set datagram address.
* <p>
* The actual addressing scheme is implementation-dependent.
* Please read the general comments on datagram addressing
* in <code>DatagramConnection.java</code>.
* <p>
* Note that if the address of a datagram is not specified, then
* it defaults to that of the connection.
*
* @param addr the new target address as a URL
* @exception IllegalArgumentException if the address is not valid
* @exception IOException if a some kind of I/O error occurs
*
* @see #getAddress
*/
public void setAddress(String addr) throws IOException;
/**
* Set datagram address, copying the address from another datagram.
*
* @param reference to the datagram whose address will be copied as
* the new target address for this datagram.
* @exception IllegalArgumentException if the address is not valid
*
* @see #getAddress
*/
public void setAddress(Datagram reference);
/**
* Set the <code>length</code> state variable.
*
* @param len the new length of the datagram
* @exception IllegalArgumentException if the length or length plus offset
* fall outside the buffer
*
* @see #getLength
*/
public void setLength(int len);
/**
* Set the <code>buffer</code>, <code>offset</code> and <code>length</code>
* state variables. Depending on the implementation, this operation may
* copy the buffer or just set the state variable <code>buffer</code>
* to the value of the <code>buffer</code> argument. However,
* the user must not assume that the contents of the internal data
* buffer can be manipulated by modifying the buffer passed on to
* this operation.
*
* @param buffer the data buffer
* @param offset the offset into the data buffer
* @param len the length of the data in the buffer
* @exception IllegalArgumentException if the length or offset
* or offset plus length fall outside the
* buffer, or if the buffer parameter is invalid
* @see #getData
*/
public void setData(byte[] buffer, int offset, int len);
/**
* Zero the <code>read/write pointer</code> as well as the
* <code>offset</code> and <code>length</code> state variables.
*/
public void reset();
}
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