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/**
 * 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.master.snapshot;

import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.classification.InterfaceStability;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.HRegionInfo;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.catalog.MetaReader;
import org.apache.hadoop.hbase.master.MasterServices;
import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos.SnapshotDescription;
import org.apache.hadoop.hbase.protobuf.generated.SnapshotProtos.SnapshotRegionManifest;
import org.apache.hadoop.hbase.snapshot.ClientSnapshotDescriptionUtils;
import org.apache.hadoop.hbase.snapshot.CorruptedSnapshotException;
import org.apache.hadoop.hbase.snapshot.SnapshotDescriptionUtils;
import org.apache.hadoop.hbase.snapshot.SnapshotManifest;
import org.apache.hadoop.hbase.snapshot.SnapshotReferenceUtil;

/**
 * General snapshot verification on the master.
 * 
 * This is a light-weight verification mechanism for all the files in a snapshot. It doesn't
 * attempt to verify that the files are exact copies (that would be paramount to taking the
 * snapshot again!), but instead just attempts to ensure that the files match the expected
 * files and are the same length.
 * 

 * Taking an online snapshots can race against other operations and this is an last line of
 * defense.  For example, if meta changes between when snapshots are taken not all regions of a
 * table may be present.  This can be caused by a region split (daughters present on this scan,
 * but snapshot took parent), or move (snapshots only checks lists of region servers, a move could
 * have caused a region to be skipped or done twice).
 * 

 * Current snapshot files checked:
 * 

 * SnapshotDescription is readable
 * Table info is readable
 * Regions
 * 
 * Matching regions in the snapshot as currently in the table
 * {@link HRegionInfo} matches the current and stored regions
 * All referenced hfiles have valid names
 * All the hfiles are present (either in .archive directory in the region)
 * All recovered.edits files are present (by name) and have the correct file size
 * 
 * 
 */
@InterfaceAudience.Private
@InterfaceStability.Unstable
public final class MasterSnapshotVerifier {
  private static final Log LOG = LogFactory.getLog(MasterSnapshotVerifier.class);

  private SnapshotDescription snapshot;
  private FileSystem fs;
  private Path rootDir;
  private TableName tableName;
  private MasterServices services;

  /**
   * @param services services for the master
   * @param snapshot snapshot to check
   * @param rootDir root directory of the hbase installation.
   */
  public MasterSnapshotVerifier(MasterServices services, SnapshotDescription snapshot, Path rootDir) {
    this.fs = services.getMasterFileSystem().getFileSystem();
    this.services = services;
    this.snapshot = snapshot;
    this.rootDir = rootDir;
    this.tableName = TableName.valueOf(snapshot.getTable());
  }

  /**
   * Verify that the snapshot in the directory is a valid snapshot
   * @param snapshotDir snapshot directory to check
   * @param snapshotServers {@link ServerName} of the servers that are involved in the snapshot
   * @throws CorruptedSnapshotException if the snapshot is invalid
   * @throws IOException if there is an unexpected connection issue to the filesystem
   */
  public void verifySnapshot(Path snapshotDir, Set snapshotServers)
      throws CorruptedSnapshotException, IOException {
    SnapshotManifest manifest = SnapshotManifest.open(services.getConfiguration(), fs,
                                                      snapshotDir, snapshot);
    // verify snapshot info matches
    verifySnapshotDescription(snapshotDir);

    // check that tableinfo is a valid table description
    verifyTableInfo(manifest);

    // check that each region is valid
    verifyRegions(manifest);
  }

  /**
   * Check that the snapshot description written in the filesystem matches the current snapshot
   * @param snapshotDir snapshot directory to check
   */
  private void verifySnapshotDescription(Path snapshotDir) throws CorruptedSnapshotException {
    SnapshotDescription found = SnapshotDescriptionUtils.readSnapshotInfo(fs, snapshotDir);
    if (!this.snapshot.equals(found)) {
      throw new CorruptedSnapshotException("Snapshot read (" + found
          + ") doesn't equal snapshot we ran (" + snapshot + ").", snapshot);
    }
  }

  /**
   * Check that the table descriptor for the snapshot is a valid table descriptor
   * @param manifest snapshot manifest to inspect
   */
  private void verifyTableInfo(final SnapshotManifest manifest) throws IOException {
    HTableDescriptor htd = manifest.getTableDescriptor();
    if (htd == null) {
      throw new CorruptedSnapshotException("Missing Table Descriptor", snapshot);
    }

    if (!htd.getNameAsString().equals(snapshot.getTable())) {
      throw new CorruptedSnapshotException("Invalid Table Descriptor. Expected "
        + snapshot.getTable() + " name, got " + htd.getNameAsString(), snapshot);
    }
  }

  /**
   * Check that all the regions in the snapshot are valid, and accounted for.
   * @param manifest snapshot manifest to inspect
   * @throws IOException if we can't reach hbase:meta or read the files from the FS
   */
  private void verifyRegions(final SnapshotManifest manifest) throws IOException {
    List regions = MetaReader.getTableRegions(this.services.getCatalogTracker(),
        tableName);

    Map regionManifests = manifest.getRegionManifestsMap();
    if (regionManifests == null) {
      String msg = "Snapshot " + ClientSnapshotDescriptionUtils.toString(snapshot) + " looks empty";
      LOG.error(msg);
      throw new CorruptedSnapshotException(msg);
    }

    String errorMsg = "";
    if (regionManifests.size() != regions.size()) {
      errorMsg = "Regions moved during the snapshot '" +
                   ClientSnapshotDescriptionUtils.toString(snapshot) + "'. expected=" +
                   regions.size() + " snapshotted=" + regionManifests.size() + ".";
      LOG.error(errorMsg);
    }

    // Verify HRegionInfo
    for (HRegionInfo region : regions) {
      SnapshotRegionManifest regionManifest = regionManifests.get(region.getEncodedName());
      if (regionManifest == null) {
        // could happen due to a move or split race.
        String mesg = " No snapshot region directory found for region:" + region;
        if (errorMsg.isEmpty()) errorMsg = mesg;
        LOG.error(mesg);
        continue;
      }

      verifyRegionInfo(region, regionManifest);
    }

    if (!errorMsg.isEmpty()) {
      throw new CorruptedSnapshotException(errorMsg);
    }

    // Verify Snapshot HFiles
    SnapshotReferenceUtil.verifySnapshot(services.getConfiguration(), fs, manifest);
  }

  /**
   * Verify that the regionInfo is valid
   * @param region the region to check
   * @param manifest snapshot manifest to inspect
   */
  private void verifyRegionInfo(final HRegionInfo region,
      final SnapshotRegionManifest manifest) throws IOException {
    HRegionInfo manifestRegionInfo = HRegionInfo.convert(manifest.getRegionInfo());
    if (!region.equals(manifestRegionInfo)) {
      String msg = "Manifest region info " + manifestRegionInfo +
                   "doesn't match expected region:" + region;
      throw new CorruptedSnapshotException(msg, snapshot);
    }
  }
}