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This nifi-utils module should be a general purpose place to store widely and generally useful functions that any component might want to leverage. NO DEPENDENCIES should be added. This module is likely to be leveraged by every extension and should not bring along any other dependencies. The only dependency intended is the nifi-api and even this is expected to be already provided in any case where it would be used. The typical place this util would be found is within a nar and all nars already have nifi-api as a parent dependency. The nifi-api can be thought of as a NiFi Application Container level dependency.

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/*
 * 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.nifi.remote.io.socket;

import java.nio.ByteBuffer;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class BufferStateManager {

    private static final Logger logger = LoggerFactory.getLogger(BufferStateManager.class);

    private ByteBuffer buffer;
    private Direction direction = Direction.WRITE;

    public BufferStateManager(final ByteBuffer buffer) {
        this.buffer = buffer;
    }

    public BufferStateManager(final ByteBuffer buffer, final Direction direction) {
        this.buffer = buffer;
        this.direction = direction;
    }

    /**
     * Ensures that the buffer is at least as big as the size specified, resizing the buffer if necessary. This operation MAY change the direction of the buffer.
     *
     * @param requiredSize the desired size of the buffer
     */
    public void ensureSize(final int requiredSize) {
        if (buffer.capacity() < requiredSize) {
            final ByteBuffer newBuffer = ByteBuffer.allocate(requiredSize);

            // we have to read buffer so make sure the direction is correct.
            if (direction == Direction.WRITE) {
                buffer.flip();
            }

            // Copy from buffer to newBuffer
            newBuffer.put(buffer);

            // Swap the buffers
            buffer = newBuffer;

            // the new buffer is ready to be written to
            direction = Direction.WRITE;
        }
    }

    public ByteBuffer prepareForWrite(final int requiredSize) {
        ensureSize(requiredSize);

        if (direction == Direction.READ) {
            direction = Direction.WRITE;
            buffer.position(buffer.limit());
        }

        buffer.limit(buffer.capacity());
        return buffer;
    }

    public ByteBuffer prepareForRead(final int requiredSize) {
        ensureSize(requiredSize);

        if (direction == Direction.WRITE) {
            direction = Direction.READ;
            buffer.flip();
        }

        return buffer;
    }

    /**
     * Clears the contents of the buffer and sets direction to WRITE
     */
    public void clear() {
        logger.debug("Clearing {}", buffer);
        buffer.clear();
        direction = Direction.WRITE;
    }

    public void compact() {
        final String before = buffer.toString();
        buffer.compact();
        logger.debug("Before compact: {}, after: {}", before, buffer);
        direction = Direction.WRITE;
    }

    public static enum Direction {

        READ, WRITE;
    }

}