[HUDI-757] Added hudi-cli command to export metadata of Instants.

Example:
hudi:db.table-> export instants --localFolder /tmp/ --limit 5 --actions clean,rollback,commit --desc false

hudi-cli/src/main/java/org/apache/hudi/cli/commands/ExportCommand.java

@@ -0,0 +1,231 @@
+/*
+ * 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.hudi.cli.commands;
+
+import org.apache.hudi.avro.HoodieAvroUtils;
+import org.apache.hudi.avro.model.HoodieArchivedMetaEntry;
+import org.apache.hudi.avro.model.HoodieCleanMetadata;
+import org.apache.hudi.avro.model.HoodieRollbackMetadata;
+import org.apache.hudi.avro.model.HoodieSavepointMetadata;
+import org.apache.hudi.cli.HoodieCLI;
+import org.apache.hudi.common.fs.FSUtils;
+import org.apache.hudi.common.model.HoodieLogFile;
+import org.apache.hudi.common.table.HoodieTableMetaClient;
+import org.apache.hudi.common.table.log.HoodieLogFormat;
+import org.apache.hudi.common.table.log.HoodieLogFormat.Reader;
+import org.apache.hudi.common.table.log.block.HoodieAvroDataBlock;
+import org.apache.hudi.common.table.timeline.HoodieActiveTimeline;
+import org.apache.hudi.common.table.timeline.HoodieInstant;
+import org.apache.hudi.common.table.timeline.HoodieTimeline;
+import org.apache.hudi.common.table.timeline.TimelineMetadataUtils;
+import org.apache.hudi.exception.HoodieException;
+import org.apache.log4j.LogManager;
+import org.apache.log4j.Logger;
+import org.apache.avro.generic.GenericRecord;
+import org.apache.avro.generic.IndexedRecord;
+import org.apache.avro.specific.SpecificData;
+import org.apache.hadoop.fs.FileStatus;
+import org.apache.hadoop.fs.Path;
+import org.springframework.shell.core.CommandMarker;
+import org.springframework.shell.core.annotation.CliCommand;
+import org.springframework.shell.core.annotation.CliOption;
+import org.springframework.stereotype.Component;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/**
+ * CLI commands to export various information from a HUDI dataset.
+ *
+ * "export instants": Export Instants and their metadata from the Timeline to a local
+ *                    directory specified by the parameter --localFolder
+ *      The instants are exported in the json format.
+ */
+@Component
+public class ExportCommand implements CommandMarker {
+
+  @CliCommand(value = "export instants", help = "Export Instants and their metadata from the Timeline")
+  public String exportInstants(
+      @CliOption(key = {"limit"}, help = "Limit Instants", unspecifiedDefaultValue = "-1") final Integer limit,
+      @CliOption(key = {"actions"}, help = "Comma seperated list of Instant actions to export",
+        unspecifiedDefaultValue = "clean,commit,deltacommit,rollback,savepoint,restore") final String filter,
+      @CliOption(key = {"desc"}, help = "Ordering", unspecifiedDefaultValue = "false") final boolean descending,
+      @CliOption(key = {"localFolder"}, help = "Local Folder to export to", mandatory = true) String localFolder)
+      throws Exception {
+
+    final String basePath = HoodieCLI.getTableMetaClient().getBasePath();
+    final Path archivePath = new Path(basePath + "/.hoodie/.commits_.archive*");
+    final Set<String> actionSet = new HashSet<String>(Arrays.asList(filter.split(",")));
+    int numExports = limit == -1 ? Integer.MAX_VALUE : limit;
+    int numCopied = 0;
+
+    if (! new File(localFolder).isDirectory()) {
+      throw new HoodieException(localFolder + " is not a valid local directory");
+    }
+
+    // The non archived instants can be listed from the Timeline.
+    HoodieTimeline timeline = HoodieCLI.getTableMetaClient().getActiveTimeline().filterCompletedInstants()
+        .filter(i -> actionSet.contains(i.getAction()));
+    List<HoodieInstant> nonArchivedInstants = timeline.getInstants().collect(Collectors.toList());
+
+    // Archived instants are in the commit archive files
+    FileStatus[] statuses = FSUtils.getFs(basePath, HoodieCLI.conf).globStatus(archivePath);
+    List<FileStatus> archivedStatuses = Arrays.stream(statuses).sorted((f1, f2) -> (int)(f1.getModificationTime() - f2.getModificationTime())).collect(Collectors.toList());
+
+    if (descending) {
+      Collections.reverse(nonArchivedInstants);
+      numCopied = copyNonArchivedInstants(nonArchivedInstants, numExports, localFolder);
+      if (numCopied < numExports) {
+        Collections.reverse(archivedStatuses);
+        numCopied += copyArchivedInstants(archivedStatuses, actionSet, numExports - numCopied, localFolder);
+      }
+    } else {
+      numCopied = copyArchivedInstants(archivedStatuses, actionSet, numExports, localFolder);
+      if (numCopied < numExports) {
+        numCopied += copyNonArchivedInstants(nonArchivedInstants, numExports - numCopied, localFolder);
+      }
+    }
+
+    return "Exported " + numCopied + " Instants to " + localFolder;
+  }
+
+  private int copyArchivedInstants(List<FileStatus> statuses, Set<String> actionSet, int limit, String localFolder) throws Exception {
+    int copyCount = 0;
+
+    for (FileStatus fs : statuses) {
+      // read the archived file
+      Reader reader = HoodieLogFormat.newReader(FSUtils.getFs(HoodieCLI.getTableMetaClient().getBasePath(), HoodieCLI.conf),
+          new HoodieLogFile(fs.getPath()), HoodieArchivedMetaEntry.getClassSchema());
+
+      // read the avro blocks
+      while (reader.hasNext() && copyCount < limit) {
+        HoodieAvroDataBlock blk = (HoodieAvroDataBlock) reader.next();
+        for (IndexedRecord ir : blk.getRecords()) {
+          // Archived instants are saved as arvo encoded HoodieArchivedMetaEntry records. We need to get the
+          // metadata record from the entry and convert it to json.
+          HoodieArchivedMetaEntry archiveEntryRecord = (HoodieArchivedMetaEntry) SpecificData.get()
+              .deepCopy(HoodieArchivedMetaEntry.SCHEMA$, ir);
+
+          final String action = archiveEntryRecord.get("actionType").toString();
+          if (!actionSet.contains(action)) {
+            continue;
+          }
+
+          GenericRecord metadata = null;
+          switch (action) {
+            case HoodieTimeline.CLEAN_ACTION:
+              metadata = archiveEntryRecord.getHoodieCleanMetadata();
+              break;
+            case HoodieTimeline.COMMIT_ACTION:
+            case HoodieTimeline.DELTA_COMMIT_ACTION:
+              metadata = archiveEntryRecord.getHoodieCommitMetadata();
+              break;
+            case HoodieTimeline.ROLLBACK_ACTION:
+              metadata = archiveEntryRecord.getHoodieRollbackMetadata();
+              break;
+            case HoodieTimeline.SAVEPOINT_ACTION:
+              metadata = archiveEntryRecord.getHoodieSavePointMetadata();
+              break;
+            case HoodieTimeline.COMPACTION_ACTION:
+              metadata = archiveEntryRecord.getHoodieCompactionMetadata();
+              break;
+            default:
+              throw new HoodieException("Unknown type of action " + action);
+          }
+
+          final String instantTime = archiveEntryRecord.get("commitTime").toString();
+          final String outPath = localFolder + Path.SEPARATOR + instantTime + "." + action;
+          writeToFile(outPath, HoodieAvroUtils.avroToJson(metadata, true));
+          if (++copyCount == limit) {
+            break;
+          }
+        }
+      }
+
+      reader.close();
+    }
+
+    return copyCount;
+  }
+
+  private int copyNonArchivedInstants(List<HoodieInstant> instants, int limit, String localFolder) throws Exception {
+    int copyCount = 0;
+
+    if (instants.isEmpty()) {
+      return limit;
+    }
+    final Logger LOG = LogManager.getLogger(ExportCommand.class);
+
+    final HoodieTableMetaClient metaClient = HoodieCLI.getTableMetaClient();
+    final HoodieActiveTimeline timeline = metaClient.getActiveTimeline();
+    for (HoodieInstant instant : instants) {
+      String localPath = localFolder + File.separator + instant.getFileName();
+
+      byte[] data = null;
+      switch (instant.getAction()) {
+        case HoodieTimeline.CLEAN_ACTION: {
+          HoodieCleanMetadata metadata = TimelineMetadataUtils.deserializeHoodieCleanMetadata(
+              timeline.getInstantDetails(instant).get());
+          data = HoodieAvroUtils.avroToJson(metadata, true);
+          break;
+        }
+        case HoodieTimeline.DELTA_COMMIT_ACTION:
+        case HoodieTimeline.COMMIT_ACTION:
+        case HoodieTimeline.COMPACTION_ACTION: {
+          // Already in json format
+          data = timeline.getInstantDetails(instant).get();
+          break;
+        }
+        case HoodieTimeline.ROLLBACK_ACTION: {
+          HoodieRollbackMetadata metadata = TimelineMetadataUtils.deserializeHoodieRollbackMetadata(
+              timeline.getInstantDetails(instant).get());
+          data = HoodieAvroUtils.avroToJson(metadata, true);
+          break;
+        }
+        case HoodieTimeline.SAVEPOINT_ACTION: {
+          HoodieSavepointMetadata metadata = TimelineMetadataUtils.deserializeHoodieSavepointMetadata(
+              timeline.getInstantDetails(instant).get());
+          data = HoodieAvroUtils.avroToJson(metadata, true);
+          break;
+        }
+        default: {
+          throw new HoodieException("Unknown type of action " + instant.getAction());
+        }
+      }
+
+      if (data != null) {
+        writeToFile(localPath, data);
+      }
+    }
+
+    return copyCount;
+  }
+
+  private void writeToFile(String path, byte[] data) throws Exception {
+    FileOutputStream writer = new FileOutputStream(path);
+    writer.write(data);
+    writer.close();
+  }
+}

hudi-common/src/main/java/org/apache/hudi/avro/HoodieAvroUtils.java

@@ -30,8 +30,11 @@ import org.apache.avro.generic.GenericDatumWriter;
 import org.apache.avro.generic.GenericRecord;
 import org.apache.avro.io.BinaryDecoder;
 import org.apache.avro.io.BinaryEncoder;
+import org.apache.avro.io.DatumWriter;
 import org.apache.avro.io.DecoderFactory;
 import org.apache.avro.io.EncoderFactory;
+import org.apache.avro.io.JsonDecoder;
+import org.apache.avro.io.JsonEncoder;
 import org.codehaus.jackson.node.NullNode;
 
 import java.io.ByteArrayInputStream;
@@ -79,6 +82,22 @@ public class HoodieAvroUtils {
     return out.toByteArray();
   }
 
+  /**
+   * Convert a given avro record to json and return the encoded bytes.
+   *
+   * @param record The GenericRecord to convert
+   * @param pretty Whether to pretty-print the json output
+   */
+  public static byte[] avroToJson(GenericRecord record, boolean pretty) throws IOException {
+    DatumWriter<Object> writer = new GenericDatumWriter<>(record.getSchema());
+    ByteArrayOutputStream out = new ByteArrayOutputStream();
+    JsonEncoder jsonEncoder = EncoderFactory.get().jsonEncoder(record.getSchema(), out, pretty);
+    writer.write(record, jsonEncoder);
+    jsonEncoder.flush();
+    return out.toByteArray();
+    //metadata.toJsonString().getBytes(StandardCharsets.UTF_8));
+  }
+
   /**
    * Convert serialized bytes back into avro record.
    */
@@ -89,6 +108,16 @@ public class HoodieAvroUtils {
     return reader.read(null, decoder);
   }
 
+  /**
+   * Convert json bytes back into avro record.
+   */
+  public static GenericRecord jsonBytesToAvro(byte[] bytes, Schema schema) throws IOException {
+    ByteArrayInputStream bio = new ByteArrayInputStream(bytes);
+    JsonDecoder jsonDecoder = DecoderFactory.get().jsonDecoder(schema, bio);
+    GenericDatumReader<GenericRecord> reader = new GenericDatumReader<>(schema);
+    return reader.read(null, jsonDecoder);
+  }
+
   public static boolean isMetadataField(String fieldName) {
     return HoodieRecord.COMMIT_TIME_METADATA_FIELD.equals(fieldName)
         || HoodieRecord.COMMIT_SEQNO_METADATA_FIELD.equals(fieldName)

hudi-common/src/main/java/org/apache/hudi/common/table/timeline/TimelineMetadataUtils.java

@@ -132,6 +132,10 @@ public class TimelineMetadataUtils {
     return deserializeAvroMetadata(bytes, HoodieCleanMetadata.class);
   }
 
+  public static HoodieRollbackMetadata deserializeHoodieRollbackMetadata(byte[] bytes) throws IOException {
+    return deserializeAvroMetadata(bytes, HoodieRollbackMetadata.class);
+  }
+
   public static HoodieSavepointMetadata deserializeHoodieSavepointMetadata(byte[] bytes) throws IOException {
     return deserializeAvroMetadata(bytes, HoodieSavepointMetadata.class);
   }