clients/src/main/java/org/apache/kafka/common/record/LogInputStream.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.kafka.common.record;

import java.io.IOException;

/**
 * An abstraction between an underlying input stream and record iterators, a {@link LogInputStream} only returns
 * the batches at one level. For magic values 0 and 1, this means that it can either handle  iteration
 * at the top level of the log or deep iteration within the payload of a single message, but it does not attempt
 * to handle both. For magic value 2, this is only used for iterating over the top-level record batches (inner
 * records do not follow the {@link RecordBatch} interface.
 *
 * The generic typing allows for implementations which present only a view of the log entries, which enables more
 * efficient iteration when the record data is not actually needed. See for example
 * {@link FileLogInputStream.FileChannelRecordBatch} in which the record is not brought into memory until needed.
 *
 * @param <T> Type parameter of the log entry
 */
interface LogInputStream<T extends RecordBatch> {

    /**
     * Get the next record batch from the underlying input stream.
     *
     * @return The next record batch or null if there is none
     * @throws IOException for any IO errors
     */
    T nextBatch() throws IOException;
}