org.apache.flink.core.io.PostVersionedIOReadableWritable Maven / Gradle / Ivy
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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.flink.core.io;
import org.apache.flink.annotation.Internal;
import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataInputViewStreamWrapper;
import org.apache.flink.core.memory.DataOutputView;
import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;
import java.util.Arrays;
/**
* A {@link VersionedIOReadableWritable} which allows to differentiate whether the previous
* data was versioned with a {@link VersionedIOReadableWritable}. This can be used if previously
* written data was not versioned, and is to be migrated to a versioned format.
*/
@Internal
public abstract class PostVersionedIOReadableWritable extends VersionedIOReadableWritable {
/** NOTE: CANNOT CHANGE! */
private static final byte[] VERSIONED_IDENTIFIER = new byte[] {-15, -51, -123, -97};
/**
* Read from the provided {@link DataInputView in}. A flag {@code wasVersioned} can be
* used to determine whether or not the data to read was previously written
* by a {@link VersionedIOReadableWritable}.
*/
protected abstract void read(DataInputView in, boolean wasVersioned) throws IOException;
@Override
public void write(DataOutputView out) throws IOException {
out.write(VERSIONED_IDENTIFIER);
super.write(out);
}
/**
* This read attempts to first identify if the input view contains the special
* {@link #VERSIONED_IDENTIFIER} by reading and buffering the first few bytes.
* If identified to be versioned, the usual version resolution read path
* in {@link VersionedIOReadableWritable#read(DataInputView)} is invoked.
* Otherwise, we "reset" the input stream by pushing back the read buffered bytes
* into the stream.
*/
public final void read(InputStream inputStream) throws IOException {
byte[] tmp = new byte[VERSIONED_IDENTIFIER.length];
inputStream.read(tmp);
if (Arrays.equals(tmp, VERSIONED_IDENTIFIER)) {
DataInputView inputView = new DataInputViewStreamWrapper(inputStream);
super.read(inputView);
read(inputView, true);
} else {
PushbackInputStream resetStream = new PushbackInputStream(inputStream, VERSIONED_IDENTIFIER.length);
resetStream.unread(tmp);
read(new DataInputViewStreamWrapper(resetStream), false);
}
}
/**
* We do not support reading from a {@link DataInputView}, because it does not
* support pushing back already read bytes.
*/
@Override
public final void read(DataInputView in) throws IOException {
throw new UnsupportedOperationException("PostVersionedIOReadableWritable cannot read from a DataInputView.");
}
}