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package com.jme3.network.base.protocol;
import java.nio.ByteBuffer;
import java.util.LinkedList;
import com.jme3.network.Message;
import com.jme3.network.base.MessageBuffer;
import com.jme3.network.base.MessageProtocol;
/**
* A MessageBuffer implementation that will deserialize messages as they
* are returned instead of deserializing them as the data comes in. This
* allows the individual messages to be processed before later messages
* are deserialized, thus allowing the serialization process itself to be
* altered mid-stream.
*
* @author Paul Speed
*/
public class LazyMessageBuffer implements MessageBuffer {
private MessageProtocol protocol;
private final LinkedList messages = new LinkedList<>();
private ByteBuffer current;
private int size;
private Byte carry;
public LazyMessageBuffer( MessageProtocol protocol ) {
this.protocol = protocol;
}
/**
* Returns the next message in the buffer or null if there are no more
* messages in the buffer.
*/
@Override
public Message pollMessage() {
if( messages.isEmpty() ) {
return null;
}
ByteBuffer bytes = messages.removeFirst();
return protocol.toMessage(bytes);
}
/**
* Returns true if there is a message waiting in the buffer.
*/
@Override
public boolean hasMessages() {
return !messages.isEmpty();
}
/**
* Adds byte data to the message buffer. Returns true if there is
* a message waiting after this call.
*/
@Override
public boolean addBytes( ByteBuffer buffer ) {
// push the data from the buffer into as
// many messages as we can
while( buffer.remaining() > 0 ) {
if( current == null ) {
// If we have a leftover carry, then we need to
// do manual processing to get the short value.
if( carry != null ) {
byte high = carry;
byte low = buffer.get();
size = (high & 0xff) << 8 | (low & 0xff);
carry = null;
}
else if( buffer.remaining() < 2 ) {
// It's possible that the supplied buffer only has one
// byte in it... and in that case we will get an underflow
// when attempting to read the short below.
// It has to be 1 or we'd never get here. But one
// isn't enough, so we stash it away.
carry = buffer.get();
break;
} else {
// We are not currently reading an object, so
// grab the size.
// Note: this is somewhat limiting. int would
// be better.
size = buffer.getShort();
}
// Allocate the buffer into which we'll feed the
// data as we get it
current = ByteBuffer.allocate(size);
}
if( current.remaining() <= buffer.remaining() ) {
// We have at least one complete object so
// copy what we can into current, create a message,
// and then continue pulling from buffer.
// Artificially set the limit so we don't overflow
int extra = buffer.remaining() - current.remaining();
buffer.limit(buffer.position() + current.remaining());
// Now copy the data
current.put(buffer);
current.flip();
// Now set the limit back to a good value
buffer.limit(buffer.position() + extra);
// Just push the bytes and let the serialization happen later.
messages.add(current);
current = null;
// Note: I originally thought that lazy deserialization was
// going to be tricky/fancy because I'd imagined having to
// collect partial buffers, leave data in working buffers, etcetera.
// However, the buffer we are passed is reused by the caller
// (it's part of the API contract) and so we MUST copy the
// data into "something" before returning. We already know
// what size buffer the message is going to need. That can't
// change. We are already creating per-message byte buffers.
// ...so we might as well just buffer this in our queue instead.
// The alternative is to somehow have an open-ended working buffer
// that expands/shrinks as needed to accommodate the 'unknown' number
// of messages that must be buffered before the caller asks for
// one. Obviously, that's way more wasteful than just keeping
// per-message byte buffers around. We already had them anyway.
// So in the end, I probably could have just altered the original
// buffering code and called it a day... but I had to do the refactoring
// before I figured that out, and now we have the ability to more easily
// swap out protocol implementations. -pspeed:2019-09-08
} else {
// Not yet a complete object so just copy what we have
current.put(buffer);
}
}
return hasMessages();
}
}
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