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
   *
   *     https://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.avro.util;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.nio.ByteBuffer;
  import java.util.List;
  
  /** Utility to present {@link ByteBuffer} data as an {@link InputStream}. */
  public class ByteBufferInputStream extends InputStream {
    private final List<ByteBuffer> buffers;
    private int current;
  
    public ByteBufferInputStream(List<ByteBuffer> buffers) {
      this.buffers = buffers;
    }
  
    /**
     * @see InputStream#read()
     */
    @Override
    public int read() throws IOException {
      ByteBuffer buffer = getBuffer();
      if (buffer == null) {
        return -1;
      }
      return buffer.get() & 0xff;
    }
  
    /**
     * @see InputStream#read(byte[], int, int)
     */
    @Override
    public int read(byte[] b, int off, int len) throws IOException {
      if (len == 0)
        return 0;
      ByteBuffer buffer = getBuffer();
      if (buffer == null) {
        return -1;
      }
      int remaining = buffer.remaining();
      if (len > remaining) {
        buffer.get(b, off, remaining);
        return remaining;
      } else {
        buffer.get(b, off, len);
        return len;
      }
    }
  
    /**
     * Read a buffer from the input without copying, if possible.
     */
    public ByteBuffer readBuffer(int length) throws IOException {
      if (length == 0)
        return ByteBuffer.allocate(0);
      ByteBuffer buffer = getBuffer();
      if (buffer == null) {
        return ByteBuffer.allocate(0);
      }
      if (buffer.remaining() == length) { // can return current as-is?
        current++;
        return buffer; // return w/o copying
      }
      // punt: allocate a new buffer & copy into it
      ByteBuffer result = ByteBuffer.allocate(length);
      int start = 0;
      while (start < length)
        start += read(result.array(), start, length - start);
      return result;
    }
  
    /**
     * Returns the next non-empty buffer.
     */
    private ByteBuffer getBuffer() {
      while (current < buffers.size()) {
        ByteBuffer buffer = buffers.get(current);
        if (buffer.hasRemaining())
          return buffer;
        current++;
      }
      return null;
    }
  }
  