// $Id: PacketSource.java,v 1.4 2006/12/12 18:23:00 vlahan Exp $

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/** This interface specifies the generic behaviour of a packet mediator.
    The read and write operations are blocking. 
    Reads and writes may fail (e.g., for communications failure), which
    implicitly closes the mediator. It is not possible to reopen a mediator
    after it is closed (instead, a new mediator should be created).

    The packet byte array must be at least 1 byte long - the first byte
    indicates the type of packet and is used to dispatch to upper layers.

    PacketSources are point-to-point and have "at most once" semantics.
    writePacket should return true only if the packet has been received
    Note that checking this is not possible with some of our broken,
    legacy protocols, and that we will optimistically assume that packets
    sent over reliable links (e.g., tcp/ip socket to a serial forwarder)
    will be reliably delivered by tcp/ip.
 */
package net.tinyos.packet;

import java.io.*;
import net.tinyos.util.*;

public interface PacketSource
{
    /**
     * Get PacketSource name
     * @return the name of this packet source, valid for use with
     * <code>BuildSource.makeSource</code>.
     */
    public String getName();

    /**
     * Open a packet source
     * @param messages A destination for informative messages from the
     *   packet source, or null to discard these.
     * @exception IOException If the source could not be opened
     */
    public void open(Messenger messages) throws IOException;

    /**
     * Close a packet source. Closing a source must force any 
     * running <code>readPacket</code> and <code>writePacket</code>
     * operations to terminate with an IOException
     * @exception IOException Thrown if a problem occured during closing.
     *   The source is considered closed even if thos occurs.
     *   Closing a closed source does not cause this exception
     */
    public void close() throws IOException;

    /**
     * Read a packet
     * @return The packet read (newly allocated). The format is described
     *   above
     * @exception IOException If the source detected a problem. The source
     *   is automatically closed.
     */
    public byte[] readPacket() throws IOException;

    /**
     * Write a packet
     * @param packet The packet to write. The format is decribed above.
     * @return Some packet sources will return false if the packet
     *   could not be written.
     */
    public boolean writePacket(byte[] packet) throws IOException;
}
