/**
    *
    * 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.hbase.regionserver.wal;
  
  import java.io.EOFException;
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.FSDataInputStream;
  import org.apache.hadoop.hbase.codec.Codec;
  import org.apache.hadoop.hbase.io.LimitInputStream;
  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
  import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
  import org.apache.hadoop.hbase.protobuf.generated.WALProtos;
  import org.apache.hadoop.hbase.protobuf.generated.WALProtos.WALHeader.Builder;
  import org.apache.hadoop.hbase.protobuf.generated.WALProtos.WALKey;
  import org.apache.hadoop.hbase.protobuf.generated.WALProtos.WALTrailer;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.wal.WAL.Entry;
  
  import com.google.protobuf.CodedInputStream;
  
  /**
   * A Protobuf based WAL has the following structure:
   * <p>
   * &lt;PB_WAL_MAGIC&gt;&lt;WALHeader&gt;&lt;WALEdits&gt;...&lt;WALEdits&gt;&lt;Trailer&gt;
   * &lt;TrailerSize&gt; &lt;PB_WAL_COMPLETE_MAGIC&gt;
   * </p>
   * The Reader reads meta information (WAL Compression state, WALTrailer, etc) in
   * ProtobufLogReader#initReader(FSDataInputStream). A WALTrailer is an extensible structure
   * which is appended at the end of the WAL. This is empty for now; it can contain some meta
   * information such as Region level stats, etc in future.
   */
  @InterfaceAudience.LimitedPrivate({HBaseInterfaceAudience.COPROC, HBaseInterfaceAudience.PHOENIX,
    HBaseInterfaceAudience.CONFIG})
  public class ProtobufLogReader extends ReaderBase {
    private static final Log LOG = LogFactory.getLog(ProtobufLogReader.class);
    // public for WALFactory until we move everything to o.a.h.h.wal
    @InterfaceAudience.Private
    public static final byte[] PB_WAL_MAGIC = Bytes.toBytes("PWAL");
    // public for TestWALSplit
    @InterfaceAudience.Private
    public static final byte[] PB_WAL_COMPLETE_MAGIC = Bytes.toBytes("LAWP");
    /**
     * Configuration name of WAL Trailer's warning size. If a waltrailer's size is greater than the
     * configured size, providers should log a warning. e.g. this is used with Protobuf reader/writer.
     */
    static final String WAL_TRAILER_WARN_SIZE = "hbase.regionserver.waltrailer.warn.size";
    static final int DEFAULT_WAL_TRAILER_WARN_SIZE = 1024 * 1024; // 1MB
  
    protected FSDataInputStream inputStream;
    protected Codec.Decoder cellDecoder;
    protected WALCellCodec.ByteStringUncompressor byteStringUncompressor;
    protected boolean hasCompression = false;
    protected boolean hasTagCompression = false;
    // walEditsStopOffset is the position of the last byte to read. After reading the last WALEdit
    // entry in the wal, the inputstream's position is equal to walEditsStopOffset.
    private long walEditsStopOffset;
    private boolean trailerPresent;
    protected WALTrailer trailer;
    // maximum size of the wal Trailer in bytes. If a user writes/reads a trailer with size larger
    // than this size, it is written/read respectively, with a WARN message in the log.
    protected int trailerWarnSize;
    private static List<String> writerClsNames = new ArrayList<String>();
    static {
      writerClsNames.add(ProtobufLogWriter.class.getSimpleName());
    }
    
    // cell codec classname
    private String codecClsName = null;
  
    enum WALHdrResult {
      EOF,                   // stream is at EOF when method starts
     SUCCESS,
     UNKNOWN_WRITER_CLS     // name of writer class isn't recognized
   }
   
   // context for WALHdr carrying information such as Cell Codec classname
   static class WALHdrContext {
     WALHdrResult result;
     String cellCodecClsName;
     
     WALHdrContext(WALHdrResult result, String cellCodecClsName) {
       this.result = result;
       this.cellCodecClsName = cellCodecClsName;
     }
     WALHdrResult getResult() {
       return result;
     }
     String getCellCodecClsName() {
       return cellCodecClsName;
     }
   }
 
   public ProtobufLogReader() {
     super();
   }
 
   @Override
   public void close() throws IOException {
     if (this.inputStream != null) {
       this.inputStream.close();
       this.inputStream = null;
     }
   }
 
   @Override
   public long getPosition() throws IOException {
     return inputStream.getPos();
   }
 
   @Override
   public void reset() throws IOException {
     String clsName = initInternal(null, false);
     initAfterCompression(clsName); // We need a new decoder (at least).
   }
 
   @Override
   public void init(FileSystem fs, Path path, Configuration conf, FSDataInputStream stream)
       throws IOException {
     this.trailerWarnSize = conf.getInt(WAL_TRAILER_WARN_SIZE, DEFAULT_WAL_TRAILER_WARN_SIZE);
     super.init(fs, path, conf, stream);
   }
 
   @Override
   protected String initReader(FSDataInputStream stream) throws IOException {
     return initInternal(stream, true);
   }
 
   /*
    * Returns names of the accepted writer classes
    */
   public List<String> getWriterClsNames() {
     return writerClsNames;
   }
   
   /*
    * Returns the cell codec classname
    */
   public String getCodecClsName() {
       return codecClsName;
   }
 
   protected WALHdrContext readHeader(Builder builder, FSDataInputStream stream)
       throws IOException {
      boolean res = builder.mergeDelimitedFrom(stream);
      if (!res) return new WALHdrContext(WALHdrResult.EOF, null);
      if (builder.hasWriterClsName() &&
          !getWriterClsNames().contains(builder.getWriterClsName())) {
        return new WALHdrContext(WALHdrResult.UNKNOWN_WRITER_CLS, null);
      }
      String clsName = null;
      if (builder.hasCellCodecClsName()) {
        clsName = builder.getCellCodecClsName();
      }
      return new WALHdrContext(WALHdrResult.SUCCESS, clsName);
   }
 
   private String initInternal(FSDataInputStream stream, boolean isFirst)
       throws IOException {
     close();
     long expectedPos = PB_WAL_MAGIC.length;
     if (stream == null) {
       stream = fs.open(path);
       stream.seek(expectedPos);
     }
     if (stream.getPos() != expectedPos) {
       throw new IOException("The stream is at invalid position: " + stream.getPos());
     }
     // Initialize metadata or, when we reset, just skip the header.
     WALProtos.WALHeader.Builder builder = WALProtos.WALHeader.newBuilder();
     WALHdrContext hdrCtxt = readHeader(builder, stream);
     WALHdrResult walHdrRes = hdrCtxt.getResult();
     if (walHdrRes == WALHdrResult.EOF) {
       throw new EOFException("Couldn't read WAL PB header");
     }
     if (walHdrRes == WALHdrResult.UNKNOWN_WRITER_CLS) {
       throw new IOException("Got unknown writer class: " + builder.getWriterClsName());
     }
     if (isFirst) {
       WALProtos.WALHeader header = builder.build();
       this.hasCompression = header.hasHasCompression() && header.getHasCompression();
       this.hasTagCompression = header.hasHasTagCompression() && header.getHasTagCompression();
     }
     this.inputStream = stream;
     this.walEditsStopOffset = this.fileLength;
     long currentPosition = stream.getPos();
     trailerPresent = setTrailerIfPresent();
     this.seekOnFs(currentPosition);
     if (LOG.isTraceEnabled()) {
       LOG.trace("After reading the trailer: walEditsStopOffset: " + this.walEditsStopOffset
           + ", fileLength: " + this.fileLength + ", " + "trailerPresent: " + trailerPresent);
     }
     
     codecClsName = hdrCtxt.getCellCodecClsName();
     
     return hdrCtxt.getCellCodecClsName();
   }
 
   /**
    * To check whether a trailer is present in a WAL, it seeks to position (fileLength -
    * PB_WAL_COMPLETE_MAGIC.size() - Bytes.SIZEOF_INT). It reads the int value to know the size of
    * the trailer, and checks whether the trailer is present at the end or not by comparing the last
    * PB_WAL_COMPLETE_MAGIC.size() bytes. In case trailer is not present, it returns false;
    * otherwise, sets the trailer and sets this.walEditsStopOffset variable up to the point just
    * before the trailer.
    * <ul>
    * The trailer is ignored in case:
    * <li>fileLength is 0 or not correct (when file is under recovery, etc).
    * <li>the trailer size is negative.
    * </ul>
    * <p>
    * In case the trailer size > this.trailerMaxSize, it is read after a WARN message.
    * @return true if a valid trailer is present
    * @throws IOException
    */
   private boolean setTrailerIfPresent() {
     try {
       long trailerSizeOffset = this.fileLength - (PB_WAL_COMPLETE_MAGIC.length + Bytes.SIZEOF_INT);
       if (trailerSizeOffset <= 0) return false;// no trailer possible.
       this.seekOnFs(trailerSizeOffset);
       // read the int as trailer size.
       int trailerSize = this.inputStream.readInt();
       ByteBuffer buf = ByteBuffer.allocate(ProtobufLogReader.PB_WAL_COMPLETE_MAGIC.length);
       this.inputStream.readFully(buf.array(), buf.arrayOffset(), buf.capacity());
       if (!Arrays.equals(buf.array(), PB_WAL_COMPLETE_MAGIC)) {
         LOG.trace("No trailer found.");
         return false;
       }
       if (trailerSize < 0) {
         LOG.warn("Invalid trailer Size " + trailerSize + ", ignoring the trailer");
         return false;
       } else if (trailerSize > this.trailerWarnSize) {
         // continue reading after warning the user.
         LOG.warn("Please investigate WALTrailer usage. Trailer size > maximum configured size : "
           + trailerSize + " > " + this.trailerWarnSize);
       }
       // seek to the position where trailer starts.
       long positionOfTrailer = trailerSizeOffset - trailerSize;
       this.seekOnFs(positionOfTrailer);
       // read the trailer.
       buf = ByteBuffer.allocate(trailerSize);// for trailer.
       this.inputStream.readFully(buf.array(), buf.arrayOffset(), buf.capacity());
       trailer = WALTrailer.parseFrom(buf.array());
       this.walEditsStopOffset = positionOfTrailer;
       return true;
     } catch (IOException ioe) {
       LOG.warn("Got IOE while reading the trailer. Continuing as if no trailer is present.", ioe);
     }
     return false;
   }
 
   protected WALCellCodec getCodec(Configuration conf, String cellCodecClsName,
       CompressionContext compressionContext) throws IOException {
     return WALCellCodec.create(conf, cellCodecClsName, compressionContext);
   }
 
   @Override
   protected void initAfterCompression() throws IOException {
     initAfterCompression(null);
   }
   
   @Override
   protected void initAfterCompression(String cellCodecClsName) throws IOException {
     WALCellCodec codec = getCodec(this.conf, cellCodecClsName, this.compressionContext);
     this.cellDecoder = codec.getDecoder(this.inputStream);
     if (this.hasCompression) {
       this.byteStringUncompressor = codec.getByteStringUncompressor();
     }
   }
 
   @Override
   protected boolean hasCompression() {
     return this.hasCompression;
   }
 
   @Override
   protected boolean hasTagCompression() {
     return this.hasTagCompression;
   }
 
   @Override
   protected boolean readNext(Entry entry) throws IOException {
     while (true) {
       // OriginalPosition might be < 0 on local fs; if so, it is useless to us.
       long originalPosition = this.inputStream.getPos();
       if (trailerPresent && originalPosition > 0 && originalPosition == this.walEditsStopOffset) {
         return false;
       }
       WALKey.Builder builder = WALKey.newBuilder();
       long size = 0;
       try {
         long available = -1;
         try {
           int firstByte = this.inputStream.read();
           if (firstByte == -1) {
             throw new EOFException("First byte is negative");
           }
           size = CodedInputStream.readRawVarint32(firstByte, this.inputStream);
           // available may be < 0 on local fs for instance.  If so, can't depend on it.
           available = this.inputStream.available();
           if (available > 0 && available < size) {
             throw new EOFException("Available stream not enough for edit, " +
                 "inputStream.available()= " + this.inputStream.available() + ", " +
                 "entry size= " + size);
           }
           ProtobufUtil.mergeFrom(builder, new LimitInputStream(this.inputStream, size),
             (int)size);
         } catch (IOException ipbe) {
           throw (EOFException) new EOFException("Invalid PB, EOF? Ignoring; originalPosition=" +
             originalPosition + ", currentPosition=" + this.inputStream.getPos() +
             ", messageSize=" + size + ", currentAvailable=" + available).initCause(ipbe);
         }
         if (!builder.isInitialized()) {
           // TODO: not clear if we should try to recover from corrupt PB that looks semi-legit.
           //       If we can get the KV count, we could, theoretically, try to get next record.
           throw new EOFException("Partial PB while reading WAL, " +
               "probably an unexpected EOF, ignoring");
         }
         WALKey walKey = builder.build();
         entry.getKey().readFieldsFromPb(walKey, this.byteStringUncompressor);
         if (!walKey.hasFollowingKvCount() || 0 == walKey.getFollowingKvCount()) {
           LOG.trace("WALKey has no KVs that follow it; trying the next one");
           continue;
         }
         int expectedCells = walKey.getFollowingKvCount();
         long posBefore = this.inputStream.getPos();
         try {
           int actualCells = entry.getEdit().readFromCells(cellDecoder, expectedCells);
           if (expectedCells != actualCells) {
             throw new EOFException("Only read " + actualCells); // other info added in catch
           }
         } catch (Exception ex) {
           String posAfterStr = "<unknown>";
           try {
             posAfterStr = this.inputStream.getPos() + "";
           } catch (Throwable t) {
             LOG.trace("Error getting pos for error message - ignoring", t);
           }
           String message = " while reading " + expectedCells + " WAL KVs; started reading at "
               + posBefore + " and read up to " + posAfterStr;
           IOException realEofEx = extractHiddenEof(ex);
           throw (EOFException) new EOFException("EOF " + message).
               initCause(realEofEx != null ? realEofEx : ex);
         }
         if (trailerPresent && this.inputStream.getPos() > this.walEditsStopOffset) {
           LOG.error("Read WALTrailer while reading WALEdits. wal: " + this.path
               + ", inputStream.getPos(): " + this.inputStream.getPos() + ", walEditsStopOffset: "
               + this.walEditsStopOffset);
           throw new EOFException("Read WALTrailer while reading WALEdits");
         }
       } catch (EOFException eof) {
         LOG.trace("Encountered a malformed edit, seeking back to last good position in file", eof);
         // If originalPosition is < 0, it is rubbish and we cannot use it (probably local fs)
         if (originalPosition < 0) throw eof;
         // Else restore our position to original location in hope that next time through we will
         // read successfully.
         seekOnFs(originalPosition);
         return false;
       }
       return true;
     }
   }
 
   private IOException extractHiddenEof(Exception ex) {
     // There are two problems we are dealing with here. Hadoop stream throws generic exception
     // for EOF, not EOFException; and scanner further hides it inside RuntimeException.
     IOException ioEx = null;
     if (ex instanceof EOFException) {
       return (EOFException)ex;
     } else if (ex instanceof IOException) {
       ioEx = (IOException)ex;
     } else if (ex instanceof RuntimeException
         && ex.getCause() != null && ex.getCause() instanceof IOException) {
       ioEx = (IOException)ex.getCause();
     }
     if (ioEx != null) {
       if (ioEx.getMessage().contains("EOF")) return ioEx;
       return null;
     }
     return null;
   }
 
   @Override
   protected void seekOnFs(long pos) throws IOException {
     this.inputStream.seek(pos);
   }
 }