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/*
* Packet.java February 2008
*
* Copyright (C) 2008, Niall Gallagher
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
* implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
package org.simpleframework.transport;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ByteChannel;
/**
* The Packet object is used to represent a collection
* of bytes that can be written to a byte channel. The packet is used
* to provide a uniform interface to byte sequences that need to be
* transferred to the connected client. It ensures that regardless of
* the backing memory store the transport can deal with the packets
* transparently. In particular packets provide a means to ensure the
* order requested is the order delivered. It uses sequence numbers
* to ensure that the delivery is performed in an orderly manner.
*
* When using a packet it is important to note that they must always
* be closed with the close method when finished with.
* This ensures any occupied resource is released. Resources such as
* buffers can be placed back in to a pool and locks released when a
* packet is closed. Failure to close can lead to a leak in resources.
*
* @author Niall Gallagher
*
* @param org.simpleframework.transport.Writer
*/
interface Packet extends Comparable {
/**
* This is used to determine how many bytes remain within this
* packet. It represents the number of write ready bytes, so if
* the length is greater than zero the packet can be written to
* a byte channel. When length is zero the packet can be closed.
*
* @return this is the number of bytes remaining in this packet
*/
int length();
/**
* This represents the capacity of the backing store. The buffer
* is full when length is equal to capacity and it can typically
* be appended to when the length is less than the capacity. The
* only exception is when space returns zero, which
* means that the packet can not have bytes appended to it.
*
* @return this is the capacity of other backing byte storage
*/
int capacity();
/**
* This is used to determine how much space is left to append
* data to this packet. This is typically equivelant to capacity
* minus the length. However in the event that the packet uses
* a private memory store that can not be written to then this
* can return zero regardless of the capacity and length.
*
* @return the space left within the buffer to append data to
*/
int space();
/**
* The sequence number represents the order with which this is
* to be delivered to the underlying network. This allows safer
* transfer of packets in an asynchronous environment where it may
* be possible for a packet to be written out of sequence. The
* sequence number also determines the order of closure.
*
* @return this returns an increasing packet sequence number
*/
long sequence();
/**
* This method is used to determine if the buffer is a reference
* to a byte buffer rather than a copy. It is important to know if
* a packet is shared as it tells the writer whether it needs to
* block the writing thread while the packet is pending a write
* to the socket channel.
*
* @return true if the packet is a reference to the byte buffer
*/
boolean isReference();
/**
* This is used to that packets can be entered in to a priority
* queue such that they are ordered based on their sequence
* numbers. Ordering based on sequence numbers ensures that
* packets can be removed and inserted back in to the queue
* without concern for the order of their insertion.
*
* @param packet this is the packet that is to be compared
*
* @return this is negative is less than otherwise its positive
*/
int compareTo(Packet packet);
/**
* This method is used to extract the contents of the packet in
* to a duplicate packet. The purpose of this is to ensure that
* when a packet wraps a shared buffer the contents of that
* buffer can be drained in to an allocated buffer, resulting
* in a packet that can be used without read write conflicts.
*
* @return this returns the packets contents in a new buffer
*/
Packet extract() throws IOException;
/**
* This is used to encode the underlying byte sequence to text.
* Converting the byte sequence to text can be useful when either
* debugging what exactly is being sent. Also, for transports
* that require string delivery of packets this can be used.
*
* @return this returns the bytes sequence as a string object
*/
String encode() throws IOException;
/**
* This is used to encode the underlying byte sequence to text.
* Converting the byte sequence to text can be useful when either
* debugging what exactly is being sent. Also, for transports
* that require string delivery of packets this can be used.
*
* @param charset this is the character set to use for encoding
*
* @return this returns the bytes sequence as a string object
*/
String encode(String charset) throws IOException;
/**
* This will append bytes within the given buffer to the packet.
* Once invoked the packet will contain the buffer bytes, which
* will have been drained from the buffer. This effectively moves
* the bytes in the buffer to the end of the packet instance.
*
* @param buffer this is the buffer containing the bytes
*
* @return returns the number of bytes that have been moved
*/
int append(ByteBuffer buffer) throws IOException;
/**
* This will append bytes within the given buffer to the packet.
* Once invoked the packet will contain the buffer bytes, which
* will have been drained from the buffer. This effectively moves
* the bytes in the buffer to the end of the packet instance.
*
* @param buffer this is the buffer containing the bytes
* @param count this is the number of bytes that should be used
*
* @return returns the number of bytes that have been moved
*/
int append(ByteBuffer buffer, int count) throws IOException;
/**
* This write method will write the contents of the packet to the
* provided byte channel. If the whole packet can be be written
* then this will simply return the number of bytes that have.
* The number of bytes remaining within the packet after a write
* can be acquired from the length method. Once all
* of the bytes are written the packet must be closed.
*
* @param channel this is the channel to write the packet to
*
* @return this returns the number of bytes that were written
*/
int write(ByteChannel channel) throws IOException;
/**
* This write method will write the contents of the packet to the
* provided byte channel. If the whole packet can be be written
* then this will simply return the number of bytes that have.
* The number of bytes remaining within the packet after a write
* can be acquired from the length method. Once all
* of the bytes are written the packet must be closed.
*
* @param channel this is the channel to write the packet to
* @param count the number of bytes to write to the channel
*
* @return this returns the number of bytes that were written
*/
int write(ByteChannel channel, int count) throws IOException;
/**
* The close method for the packet is used to ensure
* that any resources occupied by the packet are released. These
* could be anything from internally pooled buffers to locks. If
* the packet is not closed on completion then this can result in
* a leak of resources within the associated transport.
*/
void close() throws IOException;
/**
* Provides a string representation of the state of the packet.
* This can be useful for debugging the state transitions that a
* packet will go through when being written and appended to.
*
* @return this returns a string representation for the packet
*/
String toString();
}