/*
* Segment.java February 2008
*
* Copyright (C) 2008, Niall Gallagher <niallg@users.sf.net>
*
* 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;
import java.util.Queue;
/**
* The <code>Segment</code> object is used to provide a means to remove a packet
* from an segment builder when closed. This can be used to wrap an existing
* packet and add functionality to it. Once closed this segment should no longer
* be used.
*
* @author Niall Gallagher
*/
class Segment implements Packet {
/**
* This is the packet that is being wrapped by this instance.
*/
private final Packet packet;
/**
* This is the queue that the packet is to be removed from.
*/
private final Queue queue;
/**
* Constructor for the <code>Segment</code> object. This is used to create a
* packet that wraps another packet, and removes that packet from the head
* of a given queue when it is closed.
*
* @param packet
* this is the packet that is to be wrapped
* @param queue
* this is the queue to remove the packet from
*/
public Segment(Packet packet, Queue queue) {
this.packet = packet;
this.queue = queue;
}
/**
* This is used to determine how much space is left to append data to this
* packet. This is typically equivalent 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
*/
@Override
public int space() {
return this.packet.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
*/
@Override
public long sequence() {
return this.packet.sequence();
}
/**
* 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
* <code>space</code> returns zero, which means that the packet can not have
* bytes appended to it.
*
* @return this is the capacity of other backing byte storage
*/
@Override
public int capacity() {
return this.packet.capacity();
}
/**
* 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
*/
@Override
public int length() {
return this.packet.length();
}
/**
* 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 remove and inserted back in
* to the equeue without concern for othe order of their insertion.
*
* @param other
* this is the packet that is to be compared
*
* @return this is negative is less than otherwise its positive
*/
@Override
public int compareTo(Packet other) {
return this.packet.compareTo(other);
}
/**
* 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
*/
@Override
public Packet extract() throws IOException {
return this.packet.extract();
}
/**
* 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
*/
@Override
public String encode() throws IOException {
return this.packet.encode();
}
/**
* 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 encoding
* this is the character set to use for encoding
*
* @return this returns the bytes sequence as a string object
*/
@Override
public String encode(String encoding) throws IOException {
return this.packet.encode(encoding);
}
/**
* 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
*/
@Override
public int append(ByteBuffer buffer) throws IOException {
return this.packet.append(buffer);
}
/**
* 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
*/
@Override
public int append(ByteBuffer buffer, int count) throws IOException {
return this.packet.append(buffer, count);
}
/**
* 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
* <code>length</code> 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
*/
@Override
public int write(ByteChannel channel) throws IOException {
return this.packet.write(channel);
}
/**
* 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
* <code>length</code> 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
*/
@Override
public int write(ByteChannel channel, int count) throws IOException {
return this.packet.write(channel, count);
}
/**
* This method is used to determine if the buffer is shared with another
* thread or service. It is important to know whether 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 buffer is shared with another service
*/
@Override
public boolean isReference() {
return this.packet.isReference();
}
/**
* The <code>close</code> method for the packet is used to ensure that any
* resources occupied by the packet are released. The resources held by this
* instance include pooled buffers. If the packet is not closed on
* completion then this can result in a leak of resources within the
* associated transport.
*/
@Override
public void close() throws IOException {
Object top = this.queue.peek();
if (top != this.packet)
throw new PacketException("Close out of sequence");
this.packet.close();
this.queue.poll();
}
/**
* 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
*/
@Override
public String toString() {
return this.packet.toString();
}
}