src/java/org/apache/cassandra/db/ReadResponse.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.cassandra.db;

import java.io.*;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

import org.apache.cassandra.io.IVersionedSerializer;
import org.apache.cassandra.io.util.DataOutputPlus;
import org.apache.cassandra.utils.ByteBufferUtil;

/*
 * The read response message is sent by the server when reading data
 * this encapsulates the keyspacename and the row that has been read.
 * The keyspace name is needed so that we can use it to create repairs.
 */
public class ReadResponse
{
    public static final IVersionedSerializer<ReadResponse> serializer = new ReadResponseSerializer();
    private static final AtomicReferenceFieldUpdater<ReadResponse, ByteBuffer> digestUpdater = AtomicReferenceFieldUpdater.newUpdater(ReadResponse.class, ByteBuffer.class, "digest");

    private final Row row;
    private volatile ByteBuffer digest;

    public ReadResponse(ByteBuffer digest)
    {
        this(null, digest);
        assert digest != null;
    }

    public ReadResponse(Row row)
    {
        this(row, null);
        assert row != null;
    }

    public ReadResponse(Row row, ByteBuffer digest)
    {
        this.row = row;
        this.digest = digest;
    }

    public Row row()
    {
        return row;
    }

    public ByteBuffer digest()
    {
        return digest;
    }

    public void setDigest(ByteBuffer digest)
    {
        ByteBuffer curr = this.digest;
        if (!digestUpdater.compareAndSet(this, curr, digest))
        {
            assert digest.equals(this.digest) :
                String.format("Digest mismatch : %s vs %s",
                              Arrays.toString(digest.array()),
                              Arrays.toString(this.digest.array()));
        }
    }

    public boolean isDigestQuery()
    {
        return digest != null && row == null;
    }
}

class ReadResponseSerializer implements IVersionedSerializer<ReadResponse>
{
    public void serialize(ReadResponse response, DataOutputPlus out, int version) throws IOException
    {
        out.writeInt(response.isDigestQuery() ? response.digest().remaining() : 0);
        ByteBuffer buffer = response.isDigestQuery() ? response.digest() : ByteBufferUtil.EMPTY_BYTE_BUFFER;
        out.write(buffer);
        out.writeBoolean(response.isDigestQuery());
        if (!response.isDigestQuery())
            Row.serializer.serialize(response.row(), out, version);
    }

    public ReadResponse deserialize(DataInput in, int version) throws IOException
    {
        byte[] digest = null;
        int digestSize = in.readInt();
        if (digestSize > 0)
        {
            digest = new byte[digestSize];
            in.readFully(digest, 0, digestSize);
        }
        boolean isDigest = in.readBoolean();
        assert isDigest == digestSize > 0;

        Row row = null;
        if (!isDigest)
        {
            // This is coming from a remote host
            row = Row.serializer.deserialize(in, version, ColumnSerializer.Flag.FROM_REMOTE);
        }

        return isDigest ? new ReadResponse(ByteBuffer.wrap(digest)) : new ReadResponse(row);
    }

    public long serializedSize(ReadResponse response, int version)
    {
        TypeSizes typeSizes = TypeSizes.NATIVE;
        ByteBuffer buffer = response.isDigestQuery() ? response.digest() : ByteBufferUtil.EMPTY_BYTE_BUFFER;
        int size = typeSizes.sizeof(buffer.remaining());
        size += buffer.remaining();
        size += typeSizes.sizeof(response.isDigestQuery());
        if (!response.isDigestQuery())
            size += Row.serializer.serializedSize(response.row(), version);
        return size;
    }
}