/**
 * 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.hadoop.hdfs;

import static org.apache.hadoop.hdfs.protocol.HdfsProtoUtil.vintPrefixed;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.ByteBuffer;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.fs.FSInputChecker;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
import org.apache.hadoop.hdfs.protocol.datatransfer.PacketHeader;
import org.apache.hadoop.hdfs.protocol.datatransfer.Sender;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseProto;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ClientReadStatusProto;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status;
import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
import org.apache.hadoop.hdfs.security.token.block.InvalidBlockTokenException;
import org.apache.hadoop.hdfs.server.common.HdfsConstants;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.net.NetUtils;
import org.apache.hadoop.security.token.Token;
import org.apache.hadoop.util.DataChecksum;


/** This is a wrapper around connection to datanode
 * and understands checksum, offset etc.
 *
 * Terminology:
 * <dl>
 * <dt>block</dt>
 *   <dd>The hdfs block, typically large (~64MB).
 *   </dd>
 * <dt>chunk</dt>
 *   <dd>A block is divided into chunks, each comes with a checksum.
 *       We want transfers to be chunk-aligned, to be able to
 *       verify checksums.
 *   </dd>
 * <dt>packet</dt>
 *   <dd>A grouping of chunks used for transport. It contains a
 *       header, followed by checksum data, followed by real data.
 *   </dd>
 * </dl>
 * Please see DataNode for the RPC specification.
 */
@InterfaceAudience.Private
public class BlockReader extends FSInputChecker {

  Socket dnSock; //for now just sending the status code (e.g. checksumOk) after the read.
  private DataInputStream in;
  private DataChecksum checksum;

  /** offset in block of the last chunk received */
  private long lastChunkOffset = -1;
  private long lastChunkLen = -1;
  private long lastSeqNo = -1;

  /** offset in block where reader wants to actually read */
  private long startOffset;

  /** offset in block of of first chunk - may be less than startOffset
      if startOffset is not chunk-aligned */
  private final long firstChunkOffset;

  private int bytesPerChecksum;
  private int checksumSize;

  /**
   * The total number of bytes we need to transfer from the DN.
   * This is the amount that the user has requested plus some padding
   * at the beginning so that the read can begin on a chunk boundary.
   */
  private final long bytesNeededToFinish;

  private boolean eos = false;
  private boolean sentStatusCode = false;
  
  byte[] skipBuf = null;
  ByteBuffer checksumBytes = null;
  /** Amount of unread data in the current received packet */
  int dataLeft = 0;
  
  /* FSInputChecker interface */
  
  /* same interface as inputStream java.io.InputStream#read()
   * used by DFSInputStream#read()
   * This violates one rule when there is a checksum error:
   * "Read should not modify user buffer before successful read"
   * because it first reads the data to user buffer and then checks
   * the checksum.
   */
  @Override
  public synchronized int read(byte[] buf, int off, int len) 
                               throws IOException {
    
    // This has to be set here, *before* the skip, since we can
    // hit EOS during the skip, in the case that our entire read
    // is smaller than the checksum chunk.
    boolean eosBefore = eos;

    //for the first read, skip the extra bytes at the front.
    if (lastChunkLen < 0 && startOffset > firstChunkOffset && len > 0) {
      // Skip these bytes. But don't call this.skip()!
      int toSkip = (int)(startOffset - firstChunkOffset);
      if ( skipBuf == null ) {
        skipBuf = new byte[bytesPerChecksum];
      }
      if ( super.read(skipBuf, 0, toSkip) != toSkip ) {
        // should never happen
        throw new IOException("Could not skip required number of bytes");
      }
    }
    
    int nRead = super.read(buf, off, len);

    // if eos was set in the previous read, send a status code to the DN
    if (eos && !eosBefore && nRead >= 0) {
      if (needChecksum()) {
        sendReadResult(dnSock, Status.CHECKSUM_OK);
      } else {
        sendReadResult(dnSock, Status.SUCCESS);
      }
    }
    return nRead;
  }

  @Override
  public synchronized long skip(long n) throws IOException {
    /* How can we make sure we don't throw a ChecksumException, at least
     * in majority of the cases?. This one throws. */  
    if ( skipBuf == null ) {
      skipBuf = new byte[bytesPerChecksum]; 
    }

    long nSkipped = 0;
    while ( nSkipped < n ) {
      int toSkip = (int)Math.min(n-nSkipped, skipBuf.length);
      int ret = read(skipBuf, 0, toSkip);
      if ( ret <= 0 ) {
        return nSkipped;
      }
      nSkipped += ret;
    }
    return nSkipped;
  }

  @Override
  public int read() throws IOException {
    throw new IOException("read() is not expected to be invoked. " +
                          "Use read(buf, off, len) instead.");
  }
  
  @Override
  public boolean seekToNewSource(long targetPos) throws IOException {
    /* Checksum errors are handled outside the BlockReader. 
     * DFSInputStream does not always call 'seekToNewSource'. In the 
     * case of pread(), it just tries a different replica without seeking.
     */ 
    return false;
  }
  
  @Override
  public void seek(long pos) throws IOException {
    throw new IOException("Seek() is not supported in BlockInputChecker");
  }

  @Override
  protected long getChunkPosition(long pos) {
    throw new RuntimeException("getChunkPosition() is not supported, " +
                               "since seek is not required");
  }
  
  /**
   * Makes sure that checksumBytes has enough capacity 
   * and limit is set to the number of checksum bytes needed 
   * to be read.
   */
  private void adjustChecksumBytes(int dataLen) {
    int requiredSize = 
      ((dataLen + bytesPerChecksum - 1)/bytesPerChecksum)*checksumSize;
    if (checksumBytes == null || requiredSize > checksumBytes.capacity()) {
      checksumBytes =  ByteBuffer.wrap(new byte[requiredSize]);
    } else {
      checksumBytes.clear();
    }
    checksumBytes.limit(requiredSize);
  }
  
  @Override
  protected synchronized int readChunk(long pos, byte[] buf, int offset, 
                                       int len, byte[] checksumBuf) 
                                       throws IOException {
    // Read one chunk.
    if (eos) {
      // Already hit EOF
      return -1;
    }
    
    // Read one DATA_CHUNK.
    long chunkOffset = lastChunkOffset;
    if ( lastChunkLen > 0 ) {
      chunkOffset += lastChunkLen;
    }
    
    // pos is relative to the start of the first chunk of the read.
    // chunkOffset is relative to the start of the block.
    // This makes sure that the read passed from FSInputChecker is the
    // for the same chunk we expect to be reading from the DN.
    if ( (pos + firstChunkOffset) != chunkOffset ) {
      throw new IOException("Mismatch in pos : " + pos + " + " + 
                            firstChunkOffset + " != " + chunkOffset);
    }

    // Read next packet if the previous packet has been read completely.
    if (dataLeft <= 0) {
      //Read packet headers.
      PacketHeader header = new PacketHeader();
      header.readFields(in);

      if (LOG.isDebugEnabled()) {
        LOG.debug("DFSClient readChunk got header " + header);
      }

      // Sanity check the lengths
      if (!header.sanityCheck(lastSeqNo)) {
           throw new IOException("BlockReader: error in packet header " +
                                 header);
      }

      lastSeqNo = header.getSeqno();
      dataLeft = header.getDataLen();
      adjustChecksumBytes(header.getDataLen());
      if (header.getDataLen() > 0) {
        IOUtils.readFully(in, checksumBytes.array(), 0,
                          checksumBytes.limit());
      }
    }

    // Sanity checks
    assert len >= bytesPerChecksum;
    assert checksum != null;
    assert checksumSize == 0 || (checksumBuf.length % checksumSize == 0);


    int checksumsToRead, bytesToRead;

    if (checksumSize > 0) {

      // How many chunks left in our packet - this is a ceiling
      // since we may have a partial chunk at the end of the file
      int chunksLeft = (dataLeft - 1) / bytesPerChecksum + 1;

      // How many chunks we can fit in databuffer
      //  - note this is a floor since we always read full chunks
      int chunksCanFit = Math.min(len / bytesPerChecksum,
                                  checksumBuf.length / checksumSize);

      // How many chunks should we read
      checksumsToRead = Math.min(chunksLeft, chunksCanFit);
      // How many bytes should we actually read
      bytesToRead = Math.min(
        checksumsToRead * bytesPerChecksum, // full chunks
        dataLeft); // in case we have a partial
    } else {
      // no checksum
      bytesToRead = Math.min(dataLeft, len);
      checksumsToRead = 0;
    }

    if ( bytesToRead > 0 ) {
      // Assert we have enough space
      assert bytesToRead <= len;
      assert checksumBytes.remaining() >= checksumSize * checksumsToRead;
      assert checksumBuf.length >= checksumSize * checksumsToRead;
      IOUtils.readFully(in, buf, offset, bytesToRead);
      checksumBytes.get(checksumBuf, 0, checksumSize * checksumsToRead);
    }

    dataLeft -= bytesToRead;
    assert dataLeft >= 0;

    lastChunkOffset = chunkOffset;
    lastChunkLen = bytesToRead;

    // If there's no data left in the current packet after satisfying
    // this read, and we have satisfied the client read, we expect
    // an empty packet header from the DN to signify this.
    // Note that pos + bytesToRead may in fact be greater since the
    // DN finishes off the entire last chunk.
    if (dataLeft == 0 &&
        pos + bytesToRead >= bytesNeededToFinish) {

      // Read header
      PacketHeader hdr = new PacketHeader();
      hdr.readFields(in);

      if (!hdr.isLastPacketInBlock() ||
          hdr.getDataLen() != 0) {
        throw new IOException("Expected empty end-of-read packet! Header: " +
                              hdr);
      }

      eos = true;
    }

    if ( bytesToRead == 0 ) {
      return -1;
    }

    return bytesToRead;
  }
  
  private BlockReader(String file, String bpid, long blockId,
      DataInputStream in, DataChecksum checksum, boolean verifyChecksum,
      long startOffset, long firstChunkOffset, long bytesToRead, Socket dnSock) {
    // Path is used only for printing block and file information in debug
    super(new Path("/blk_" + blockId + ":" + bpid + ":of:"+ file)/*too non path-like?*/,
          1, verifyChecksum,
          checksum.getChecksumSize() > 0? checksum : null, 
          checksum.getBytesPerChecksum(),
          checksum.getChecksumSize());
    
    this.dnSock = dnSock;
    this.in = in;
    this.checksum = checksum;
    this.startOffset = Math.max( startOffset, 0 );

    // The total number of bytes that we need to transfer from the DN is
    // the amount that the user wants (bytesToRead), plus the padding at
    // the beginning in order to chunk-align. Note that the DN may elect
    // to send more than this amount if the read starts/ends mid-chunk.
    this.bytesNeededToFinish = bytesToRead + (startOffset - firstChunkOffset);

    this.firstChunkOffset = firstChunkOffset;
    lastChunkOffset = firstChunkOffset;
    lastChunkLen = -1;

    bytesPerChecksum = this.checksum.getBytesPerChecksum();
    checksumSize = this.checksum.getChecksumSize();
  }

  public static BlockReader newBlockReader(Socket sock, String file,
      ExtendedBlock block, Token<BlockTokenIdentifier> blockToken, 
      long startOffset, long len, int bufferSize) throws IOException {
    return newBlockReader(sock, file, block, blockToken, startOffset, len, bufferSize,
        true);
  }

  /** Java Doc required */
  public static BlockReader newBlockReader( Socket sock, String file, 
                                     ExtendedBlock block, 
                                     Token<BlockTokenIdentifier> blockToken,
                                     long startOffset, long len,
                                     int bufferSize, boolean verifyChecksum)
                                     throws IOException {
    return newBlockReader(sock, file, block, blockToken, startOffset,
                          len, bufferSize, verifyChecksum, "");
  }

  /**
   * Create a new BlockReader specifically to satisfy a read.
   * This method also sends the OP_READ_BLOCK request.
   *
   * @param sock  An established Socket to the DN. The BlockReader will not close it normally
   * @param file  File location
   * @param block  The block object
   * @param blockToken  The block token for security
   * @param startOffset  The read offset, relative to block head
   * @param len  The number of bytes to read
   * @param bufferSize  The IO buffer size (not the client buffer size)
   * @param verifyChecksum  Whether to verify checksum
   * @param clientName  Client name
   * @return New BlockReader instance, or null on error.
   */
  public static BlockReader newBlockReader( Socket sock, String file,
                                     ExtendedBlock block, 
                                     Token<BlockTokenIdentifier> blockToken,
                                     long startOffset, long len,
                                     int bufferSize, boolean verifyChecksum,
                                     String clientName)
                                     throws IOException {
    // in and out will be closed when sock is closed (by the caller)
    Sender.opReadBlock(
        new DataOutputStream(new BufferedOutputStream(
            NetUtils.getOutputStream(sock,HdfsConstants.WRITE_TIMEOUT))),
        block, startOffset, len, clientName, blockToken);
    
    //
    // Get bytes in block, set streams
    //

    DataInputStream in = new DataInputStream(
        new BufferedInputStream(NetUtils.getInputStream(sock), 
                                bufferSize));
    
    BlockOpResponseProto status = BlockOpResponseProto.parseFrom(
        vintPrefixed(in));
    if (status.getStatus() != Status.SUCCESS) {
      if (status.getStatus() == Status.ERROR_ACCESS_TOKEN) {
        throw new InvalidBlockTokenException(
            "Got access token error for OP_READ_BLOCK, self="
                + sock.getLocalSocketAddress() + ", remote="
                + sock.getRemoteSocketAddress() + ", for file " + file
                + ", for pool " + block.getBlockPoolId() + " block " 
                + block.getBlockId() + "_" + block.getGenerationStamp());
      } else {
        throw new IOException("Got error for OP_READ_BLOCK, self="
            + sock.getLocalSocketAddress() + ", remote="
            + sock.getRemoteSocketAddress() + ", for file " + file
            + ", for pool " + block.getBlockPoolId() + " block " 
            + block.getBlockId() + "_" + block.getGenerationStamp());
      }
    }
    DataChecksum checksum = DataChecksum.newDataChecksum( in );
    //Warning when we get CHECKSUM_NULL?
    
    // Read the first chunk offset.
    long firstChunkOffset = in.readLong();
    
    if ( firstChunkOffset < 0 || firstChunkOffset > startOffset ||
        firstChunkOffset >= (startOffset + checksum.getBytesPerChecksum())) {
      throw new IOException("BlockReader: error in first chunk offset (" +
                            firstChunkOffset + ") startOffset is " + 
                            startOffset + " for file " + file);
    }

    return new BlockReader(file, block.getBlockPoolId(), block.getBlockId(),
        in, checksum, verifyChecksum, startOffset, firstChunkOffset, len, sock);
  }

  @Override
  public synchronized void close() throws IOException {
    startOffset = -1;
    checksum = null;
    if (dnSock != null) {
      dnSock.close();
    }

    // in will be closed when its Socket is closed.
  }
  
  /** kind of like readFully(). Only reads as much as possible.
   * And allows use of protected readFully().
   */
  public int readAll(byte[] buf, int offset, int len) throws IOException {
    return readFully(this, buf, offset, len);
  }

  /**
   * Take the socket used to talk to the DN.
   */
  public Socket takeSocket() {
    assert hasSentStatusCode() :
      "BlockReader shouldn't give back sockets mid-read";
    Socket res = dnSock;
    dnSock = null;
    return res;
  }

  /**
   * Whether the BlockReader has reached the end of its input stream
   * and successfully sent a status code back to the datanode.
   */
  public boolean hasSentStatusCode() {
    return sentStatusCode;
  }

  /**
   * When the reader reaches end of the read, it sends a status response
   * (e.g. CHECKSUM_OK) to the DN. Failure to do so could lead to the DN
   * closing our connection (which we will re-open), but won't affect
   * data correctness.
   */
  void sendReadResult(Socket sock, Status statusCode) {
    assert !sentStatusCode : "already sent status code to " + sock;
    try {
      OutputStream out = NetUtils.getOutputStream(sock, HdfsConstants.WRITE_TIMEOUT);
      
      ClientReadStatusProto.newBuilder()
        .setStatus(statusCode)
        .build()
        .writeDelimitedTo(out);

      out.flush();
      sentStatusCode = true;
    } catch (IOException e) {
      // It's ok not to be able to send this. But something is probably wrong.
      LOG.info("Could not send read status (" + statusCode + ") to datanode " +
               sock.getInetAddress() + ": " + e.getMessage());
    }
  }
  
  /**
   * File name to print when accessing a block directly (from servlets)
   * @param s Address of the block location
   * @param poolId Block pool ID of the block
   * @param blockId Block ID of the block
   * @return string that has a file name for debug purposes
   */
  public static String getFileName(final InetSocketAddress s,
      final String poolId, final long blockId) {
    return s.toString() + ":" + poolId + ":" + blockId;
  }
}