content: /*
   * 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.beam.sdk.coders;
  
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
  
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.util.List;
  import org.apache.beam.sdk.util.VarInt;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.io.ByteStreams;
  
  /**
   * A {@link Coder} which is able to take any existing coder and wrap it such that it is only invoked
   * in the {@link org.apache.beam.sdk.coders.Coder.Context#OUTER outer context}. The data
   * representing the element is prefixed with a length using a variable integer encoding.
   *
   * @param <T> the type of the values being transcoded
   */
  public class LengthPrefixCoder<T> extends StructuredCoder<T> {
  
    public static <T> LengthPrefixCoder<T> of(Coder<T> valueCoder) {
      checkNotNull(valueCoder, "Coder not expected to be null");
      return new LengthPrefixCoder<>(valueCoder);
    }
  
    /////////////////////////////////////////////////////////////////////////////
  
    private final Coder<T> valueCoder;
  
    private LengthPrefixCoder(Coder<T> valueCoder) {
      this.valueCoder = valueCoder;
    }
  
    @Override
    public void encode(T value, OutputStream outStream) throws CoderException, IOException {
      ByteArrayOutputStream bos = new ByteArrayOutputStream();
      valueCoder.encode(value, bos, Context.OUTER);
      VarInt.encode(bos.size(), outStream);
      bos.writeTo(outStream);
    }
  
    @Override
    public T decode(InputStream inStream) throws CoderException, IOException {
      long size = VarInt.decodeLong(inStream);
      return valueCoder.decode(ByteStreams.limit(inStream, size), Context.OUTER);
    }
  
    @Override
    public List<? extends Coder<?>> getCoderArguments() {
      return ImmutableList.of(valueCoder);
    }
  
    /** Gets the value coder that will be prefixed by the length. */
    public Coder<T> getValueCoder() {
      return valueCoder;
    }
  
    /**
     * {@code LengthPrefixCoder} is deterministic if the nested {@code Coder} is.
     *
     * <p>{@inheritDoc}
     */
    @Override
    public void verifyDeterministic() throws NonDeterministicException {
      valueCoder.verifyDeterministic();
    }
  
    /**
     * {@code LengthPrefixCoder} is consistent with equals if the nested {@code Coder} is.
     *
     * <p>{@inheritDoc}
     */
    @Override
    public boolean consistentWithEquals() {
      return valueCoder.consistentWithEquals();
    }
  
    /**
     * Overridden to short-circuit the default {@code StructuredCoder} behavior of encoding and
     * counting the bytes. The size is known to be the size of the value plus the number of bytes
     * required to prefix the length.
     *
     * <p>{@inheritDoc}
     */
    @Override
    protected long getEncodedElementByteSize(T value) throws Exception {
      long valueSize = valueCoder.getEncodedElementByteSize(value);
      return VarInt.getLength(valueSize) + valueSize;
    }
  
    /**
     * {@code LengthPrefixCoder} is cheap if {@code valueCoder} is cheap.
     *
     * <p>{@inheritDoc}
     */
    @Override
    public boolean isRegisterByteSizeObserverCheap(T value) {
      return valueCoder.isRegisterByteSizeObserverCheap(value);
    }
  }
  