src/java/org/apache/cassandra/db/AtomDeserializer.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.DataInput;
import java.io.IOException;

import org.apache.cassandra.db.composites.CellName;
import org.apache.cassandra.db.composites.CellNameType;
import org.apache.cassandra.db.composites.Composite;
import org.apache.cassandra.io.sstable.format.Version;

/**
 * Helper class to deserialize OnDiskAtom efficiently.
 *
 * More precisely, this class is used by the low-level readers
 * (IndexedSliceReader and SSTableNamesIterator) to ensure we don't
 * do more work than necessary (i.e. we don't allocate/deserialize
 * objects for things we don't care about).
 */
public class AtomDeserializer
{
    private final CellNameType type;
    private final CellNameType.Deserializer nameDeserializer;
    private final DataInput in;
    private final ColumnSerializer.Flag flag;
    private final int expireBefore;
    private final Version version;

    // The "flag" for the next name (which correspond to the "masks" in ColumnSerializer) if it has been
    // read already, Integer.MIN_VALUE otherwise;
    private int nextFlags = Integer.MIN_VALUE;

    public AtomDeserializer(CellNameType type, DataInput in, ColumnSerializer.Flag flag, int expireBefore, Version version)
    {
        this.type = type;
        this.nameDeserializer = type.newDeserializer(in);
        this.in = in;
        this.flag = flag;
        this.expireBefore = expireBefore;
        this.version = version;
    }

    /**
     * Whether or not there is more atom to read.
     */
    public boolean hasNext() throws IOException
    {
        return nameDeserializer.hasNext();
    }

    /**
     * Whether or not some atom has been read but not processed (neither readNext() nor
     * skipNext() has been called for that atom) yet.
     */
    public boolean hasUnprocessed() throws IOException
    {
        return nameDeserializer.hasUnprocessed();
    }

    /**
     * Compare the provided composite to the next atom to read on disk.
     *
     * This will not read/deserialize the whole atom but only what is necessary for the
     * comparison. Whenever we know what to do with this atom (read it or skip it),
     * readNext or skipNext should be called.
     */
    public int compareNextTo(Composite composite) throws IOException
    {
        return nameDeserializer.compareNextTo(composite);
    }

    /**
     * Returns whether the next atom is a range tombstone or not.
     *
     * Please note that this should only be called after compareNextTo() has been called.
     */
    public boolean nextIsRangeTombstone() throws IOException
    {
        nextFlags = in.readUnsignedByte();
        return (nextFlags & ColumnSerializer.RANGE_TOMBSTONE_MASK) != 0;
    }

    /**
     * Returns the next atom.
     */
    public OnDiskAtom readNext() throws IOException
    {
        Composite name = nameDeserializer.readNext();
        assert !name.isEmpty(); // This would imply hasNext() hasn't been called

        nextFlags = nextFlags == Integer.MIN_VALUE ? in.readUnsignedByte() : nextFlags;
        OnDiskAtom atom = (nextFlags & ColumnSerializer.RANGE_TOMBSTONE_MASK) != 0
                        ? type.rangeTombstoneSerializer().deserializeBody(in, name, version)
                        : type.columnSerializer().deserializeColumnBody(in, (CellName)name, nextFlags, flag, expireBefore);
        nextFlags = Integer.MIN_VALUE;
        return atom;
    }

    /**
     * Skips the next atom.
     */
    public void skipNext() throws IOException
    {
        nameDeserializer.skipNext();
        nextFlags = nextFlags == Integer.MIN_VALUE ? in.readUnsignedByte() : nextFlags;
        if ((nextFlags & ColumnSerializer.RANGE_TOMBSTONE_MASK) != 0)
            type.rangeTombstoneSerializer().skipBody(in, version);
        else
            type.columnSerializer().skipColumnBody(in, nextFlags);
        nextFlags = Integer.MIN_VALUE;
    }
}