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/*
* Copyright 2014-2017 Real Logic Ltd.
*
* 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 io.aeron;
import io.aeron.logbuffer.FragmentHandler;
import io.aeron.logbuffer.Header;
import org.agrona.DirectBuffer;
import org.agrona.collections.Int2ObjectHashMap;
import static io.aeron.logbuffer.FrameDescriptor.*;
/**
* A {@link FragmentHandler} that sits in a chain-of-responsibility pattern that reassembles fragmented messages
* so that the next handler in the chain only sees whole messages.
*
* Unfragmented messages are delegated without copy. Fragmented messages are copied to a temporary
* buffer for reassembly before delegation.
*
* The {@link Header} passed to the delegate on assembling a message will be that of the last fragment.
*
* Session based buffers will be allocated and grown as necessary based on the length of messages to be assembled.
* When sessions go inactive see {@link UnavailableImageHandler}, it is possible to free the buffer by calling
* {@link #freeSessionBuffer(int)}.
*
* @see Subscription#poll(FragmentHandler, int)
* @see Image#poll(FragmentHandler, int)
*/
public class FragmentAssembler implements FragmentHandler
{
private final boolean isDirectByteBuffer;
private final int initialBufferLength;
private final FragmentHandler delegate;
private final Int2ObjectHashMap builderBySessionIdMap = new Int2ObjectHashMap<>();
/**
* Construct an adapter to reassemble message fragments and delegate on whole messages.
*
* @param delegate onto which whole messages are forwarded.
*/
public FragmentAssembler(final FragmentHandler delegate)
{
this(delegate, 0, false);
}
/**
* Construct an adapter to reassemble message fragments and delegate on whole messages.
*
* @param delegate onto which whole messages are forwarded.
* @param initialBufferLength to be used for each session.
*/
public FragmentAssembler(final FragmentHandler delegate, final int initialBufferLength)
{
this(delegate, initialBufferLength, false);
}
/**
* Construct an adapter to reassemble message fragments and delegate on whole messages.
*
* @param delegate onto which whole messages are forwarded.
* @param initialBufferLength to be used for each session.
* @param isDirectByteBuffer is the underlying buffer to be a direct {@link java.nio.ByteBuffer}?
*/
public FragmentAssembler(
final FragmentHandler delegate, final int initialBufferLength, final boolean isDirectByteBuffer)
{
this.initialBufferLength = initialBufferLength;
this.delegate = delegate;
this.isDirectByteBuffer = isDirectByteBuffer;
}
/**
* Get the delegate unto which assembled messages are delegated.
*
* @return the delegate unto which assembled messages are delegated.
*/
public FragmentHandler delegate()
{
return delegate;
}
/**
* Is the underlying buffer used to assemble fragments a direct {@link java.nio.ByteBuffer}?
*
* @return true if the underlying buffer used to assemble fragments is a direct {@link java.nio.ByteBuffer}
*/
public boolean isDirectByteBuffer()
{
return isDirectByteBuffer;
}
/**
* The implementation of {@link FragmentHandler} that reassembles and forwards whole messages.
*
* @param buffer containing the data.
* @param offset at which the data begins.
* @param length of the data in bytes.
* @param header representing the meta data for the data.
*/
public void onFragment(final DirectBuffer buffer, final int offset, final int length, final Header header)
{
final byte flags = header.flags();
if ((flags & UNFRAGMENTED) == UNFRAGMENTED)
{
delegate.onFragment(buffer, offset, length, header);
}
else
{
handleFragment(buffer, offset, length, header, flags);
}
}
private void handleFragment(
final DirectBuffer buffer, final int offset, final int length, final Header header, final byte flags)
{
if ((flags & BEGIN_FRAG_FLAG) == BEGIN_FRAG_FLAG)
{
final BufferBuilder builder = getBufferBuilder(header.sessionId());
builder.reset().append(buffer, offset, length);
}
else
{
final BufferBuilder builder = builderBySessionIdMap.get(header.sessionId());
if (null != builder && builder.limit() != 0)
{
builder.append(buffer, offset, length);
if ((flags & END_FRAG_FLAG) == END_FRAG_FLAG)
{
final int msgLength = builder.limit();
delegate.onFragment(builder.buffer(), 0, msgLength, header);
builder.reset();
}
}
}
}
/**
* Free an existing session buffer to reduce memory pressure when an image goes inactive or no more
* large messages are expected.
*
* @param sessionId to have its buffer freed
* @return true if a buffer has been freed otherwise false.
*/
public boolean freeSessionBuffer(final int sessionId)
{
return null != builderBySessionIdMap.remove(sessionId);
}
/**
* Clear down the cache of buffers by session for reassembling messages.
*/
public void clear()
{
builderBySessionIdMap.clear();
}
private BufferBuilder getBufferBuilder(final int sessionId)
{
BufferBuilder bufferBuilder = builderBySessionIdMap.get(sessionId);
if (null == bufferBuilder)
{
bufferBuilder = new BufferBuilder(initialBufferLength, isDirectByteBuffer);
builderBySessionIdMap.put(sessionId, bufferBuilder);
}
return bufferBuilder;
}
}