content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.client.file;
  
  import alluxio.Seekable;
  import alluxio.client.BoundedStream;
  import alluxio.client.CanUnbuffer;
  import alluxio.client.PositionedReadable;
  import alluxio.exception.PreconditionMessage;
  import alluxio.util.io.BufferUtils;
  
  import com.google.common.base.Preconditions;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.nio.ByteBuffer;
  
  /**
   * A streaming API to read a file. This API represents a file as a stream of bytes and provides a
   * collection of {@link #read} methods to access this stream of bytes. In addition, one can seek
   * into a given offset of the stream to read.
   */
  public abstract class FileInStream extends InputStream
      implements BoundedStream, PositionedReadable, Seekable, CanUnbuffer {
    private final byte[] mSingleByte = new byte[1];
  
    @Override
    public int read() throws IOException {
      int bytesRead = read(mSingleByte);
      if (bytesRead == -1) {
        return -1;
      }
      Preconditions.checkState(bytesRead == 1);
      return BufferUtils.byteToInt(mSingleByte[0]);
    }
  
    @Override
    public int read(byte[] b) throws IOException {
      Preconditions.checkNotNull(b, PreconditionMessage.ERR_READ_BUFFER_NULL);
      return read(b, 0, b.length);
    }
  
    @Override
    public int read(byte[] b, int off, int len) throws IOException {
      Preconditions.checkNotNull(b, PreconditionMessage.ERR_READ_BUFFER_NULL);
      return read(ByteBuffer.wrap(b), off, len);
    }
  
    /**
     * Reads up to buf.remaining() bytes into buf. Callers should use
     * buf.limit(..) to control the size of the desired read.
     * <p>
     * After a successful call, buf.position() will be advanced by the number
     * of bytes read and buf.limit() should be unchanged.
     * <p>
     * In the case of an exception, the values of buf.position() and buf.limit()
     * are undefined, and callers should be prepared to recover from this eventually.
     * <p>
     * Implementations should treat 0-length requests as legitimate, and must not
     * signal an error upon their receipt.
     *
     * @param buf the ByteBuffer to receive the results of the read operation
     * @return the number of bytes read, possibly zero, or -1 if reach end-of-stream
     */
    public int read(ByteBuffer buf) throws IOException {
      return read(buf, buf.position(), buf.remaining());
    }
  
    /**
     * Reads up to len bytes of data from the input stream into the byte buffer.
     *
     * @param byteBuffer the buffer into which the data is read
     * @param off the start offset in the buffer at which the data is written
     * @param len the maximum number of bytes to read
     * @return the total number of bytes read into the buffer, or -1 if there is no more
     *         data because the end of the stream has been reached
     */
    public int read(ByteBuffer byteBuffer, int off, int len) throws IOException {
      int nread = 0;
      int rd = 0;
      final int sz = len;
      final byte[] dest = new byte[sz];
      while (rd >= 0 && nread < sz) {
        rd = read(dest, nread, sz - nread);
        if (rd >= 0) {
          nread += rd;
        }
      }
      if (nread == -1) { // EOF
        nread = 0;
      } else if (nread > 0) {
        byteBuffer.put(dest, 0, nread);
      }
      return nread;
    }
  
    @Override
    public void unbuffer() {
    }
  }
  