HDFS-12473. Change hosts JSON file format.

(cherry picked from commit 230b85d5865b7e08fb7aaeab45295b5b966011ef)

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileReader.java

@@ -19,58 +19,85 @@
 package org.apache.hadoop.hdfs.util;
 
 import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.databind.JsonMappingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.ObjectReader;
+
 import java.io.FileInputStream;
 import java.io.InputStreamReader;
 import java.io.IOException;
 import java.io.Reader;
+import java.util.ArrayList;
 import java.util.Iterator;
-import java.util.Set;
-import java.util.HashSet;
+import java.util.List;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
- * Reader support for JSON based datanode configuration, an alternative
+ * Reader support for JSON-based datanode configuration, an alternative format
  * to the exclude/include files configuration.
- * The JSON file format is the array of elements where each element
+ * The JSON file format defines the array of elements where each element
  * in the array describes the properties of a datanode. The properties of
- * a datanode is defined in {@link DatanodeAdminProperties}. For example,
+ * a datanode is defined by {@link DatanodeAdminProperties}. For example,
  *
- * {"hostName": "host1"}
- * {"hostName": "host2", "port": 50, "upgradeDomain": "ud0"}
- * {"hostName": "host3", "port": 0, "adminState": "DECOMMISSIONED"}
+ * [
+ *   {"hostName": "host1"},
+ *   {"hostName": "host2", "port": 50, "upgradeDomain": "ud0"},
+ *   {"hostName": "host3", "port": 0, "adminState": "DECOMMISSIONED"}
+ * ]
  */
 @InterfaceAudience.LimitedPrivate({"HDFS"})
 @InterfaceStability.Unstable
 public final class CombinedHostsFileReader {
-  private static final ObjectReader READER =
-      new ObjectMapper().readerFor(DatanodeAdminProperties.class);
-  private static final JsonFactory JSON_FACTORY = new JsonFactory();
+
+  public static final Logger LOG =
+      LoggerFactory.getLogger(CombinedHostsFileReader.class);
 
   private CombinedHostsFileReader() {
   }
 
   /**
    * Deserialize a set of DatanodeAdminProperties from a json file.
-   * @param hostsFile the input json file to read from.
+   * @param hostsFile the input json file to read from
    * @return the set of DatanodeAdminProperties
    * @throws IOException
    */
-  public static Set<DatanodeAdminProperties>
+  public static DatanodeAdminProperties[]
       readFile(final String hostsFile) throws IOException {
-    HashSet<DatanodeAdminProperties> allDNs = new HashSet<>();
+    DatanodeAdminProperties[] allDNs = new DatanodeAdminProperties[0];
+    ObjectMapper objectMapper = new ObjectMapper();
+    boolean tryOldFormat = false;
     try (Reader input =
-         new InputStreamReader(new FileInputStream(hostsFile), "UTF-8")) {
-      Iterator<DatanodeAdminProperties> iterator =
-          READER.readValues(JSON_FACTORY.createParser(input));
-      while (iterator.hasNext()) {
-        DatanodeAdminProperties properties = iterator.next();
-        allDNs.add(properties);
+        new InputStreamReader(new FileInputStream(hostsFile), "UTF-8")) {
+      allDNs = objectMapper.readValue(input, DatanodeAdminProperties[].class);
+    } catch (JsonMappingException jme) {
+      // The old format doesn't have json top-level token to enclose the array.
+      // For backward compatibility, try parsing the old format.
+      tryOldFormat = true;
+      LOG.warn("{} has invalid JSON format." +
+          "Try the old format without top-level token defined.", hostsFile);
+    }
+
+    if (tryOldFormat) {
+      ObjectReader objectReader =
+          objectMapper.readerFor(DatanodeAdminProperties.class);
+      JsonFactory jsonFactory = new JsonFactory();
+      List<DatanodeAdminProperties> all = new ArrayList<>();
+      try (Reader input =
+          new InputStreamReader(new FileInputStream(hostsFile), "UTF-8")) {
+        Iterator<DatanodeAdminProperties> iterator =
+            objectReader.readValues(jsonFactory.createParser(input));
+        while (iterator.hasNext()) {
+          DatanodeAdminProperties properties = iterator.next();
+          all.add(properties);
+        }
       }
+      allDNs = all.toArray(new DatanodeAdminProperties[all.size()]);
     }
     return allDNs;
   }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileWriter.java

@@ -32,20 +32,21 @@ import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
 
 /**
- * Writer support for JSON based datanode configuration, an alternative
+ * Writer support for JSON-based datanode configuration, an alternative format
  * to the exclude/include files configuration.
- * The JSON file format is the array of elements where each element
+ * The JSON file format defines the array of elements where each element
  * in the array describes the properties of a datanode. The properties of
- * a datanode is defined in {@link DatanodeAdminProperties}. For example,
+ * a datanode is defined by {@link DatanodeAdminProperties}. For example,
  *
- * {"hostName": "host1"}
- * {"hostName": "host2", "port": 50, "upgradeDomain": "ud0"}
- * {"hostName": "host3", "port": 0, "adminState": "DECOMMISSIONED"}
+ * [
+ *   {"hostName": "host1"},
+ *   {"hostName": "host2", "port": 50, "upgradeDomain": "ud0"},
+ *   {"hostName": "host3", "port": 0, "adminState": "DECOMMISSIONED"}
+ * ]
  */
 @InterfaceAudience.LimitedPrivate({"HDFS"})
 @InterfaceStability.Unstable
 public final class CombinedHostsFileWriter {
-  private static final ObjectMapper MAPPER = new ObjectMapper();
   private CombinedHostsFileWriter() {
   }
 
@@ -57,13 +58,11 @@ public final class CombinedHostsFileWriter {
    */
   public static void writeFile(final String hostsFile,
       final Set<DatanodeAdminProperties> allDNs) throws IOException {
-    StringBuilder configs = new StringBuilder();
+    final ObjectMapper objectMapper = new ObjectMapper();
+
     try (Writer output =
        new OutputStreamWriter(new FileOutputStream(hostsFile), "UTF-8")) {
-      for (DatanodeAdminProperties datanodeAdminProperties: allDNs) {
-        configs.append(MAPPER.writeValueAsString(datanodeAdminProperties));
-      }
-      output.write(configs.toString());
+      objectMapper.writeValue(output, allDNs);
     }
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CombinedHostFileManager.java

@@ -39,7 +39,6 @@ import java.net.InetSocketAddress;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.Map;
-import java.util.Set;
 
 import com.google.common.base.Predicate;
 
@@ -212,7 +211,7 @@ public class CombinedHostFileManager extends HostConfigManager {
   }
   private void refresh(final String hostsFile) throws IOException {
     HostProperties hostProps = new HostProperties();
-    Set<DatanodeAdminProperties> all =
+    DatanodeAdminProperties[] all =
         CombinedHostsFileReader.readFile(hostsFile);
     for(DatanodeAdminProperties properties : all) {
       InetSocketAddress addr = parseEntry(hostsFile,

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestCombinedHostsFileReader.java

@@ -20,8 +20,6 @@ package org.apache.hadoop.hdfs.util;
 import java.io.File;
 import java.io.FileWriter;
 
-import java.util.Set;
-
 import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
 import org.apache.hadoop.test.GenericTestUtils;
 import org.junit.Before;
@@ -30,19 +28,21 @@ import org.junit.Test;
 
 import static org.junit.Assert.assertEquals;
 
-/*
- * Test for JSON based HostsFileReader
+/**
+ * Test for JSON based HostsFileReader.
  */
 public class TestCombinedHostsFileReader {
 
   // Using /test/build/data/tmp directory to store temporary files
-  static final String HOSTS_TEST_DIR = GenericTestUtils.getTestDir()
+  static final String HOSTSTESTDIR = GenericTestUtils.getTestDir()
       .getAbsolutePath();
-  File NEW_FILE = new File(HOSTS_TEST_DIR, "dfs.hosts.new.json");
+  private final File newFile = new File(HOSTSTESTDIR, "dfs.hosts.new.json");
 
-  static final String TEST_CACHE_DATA_DIR =
+  static final String TESTCACHEDATADIR =
       System.getProperty("test.cache.data", "build/test/cache");
-  File EXISTING_FILE = new File(TEST_CACHE_DATA_DIR, "dfs.hosts.json");
+  private final File jsonFile = new File(TESTCACHEDATADIR, "dfs.hosts.json");
+  private final File legacyFile =
+      new File(TESTCACHEDATADIR, "legacy.dfs.hosts.json");
 
   @Before
   public void setUp() throws Exception {
@@ -51,18 +51,28 @@ public class TestCombinedHostsFileReader {
   @After
   public void tearDown() throws Exception {
     // Delete test file after running tests
-    NEW_FILE.delete();
+    newFile.delete();
+
+  }
 
+  /*
+   * Load the legacy test json file
+   */
+  @Test
+  public void testLoadLegacyJsonFile() throws Exception {
+    DatanodeAdminProperties[] all =
+        CombinedHostsFileReader.readFile(legacyFile.getAbsolutePath());
+    assertEquals(7, all.length);
   }
 
   /*
-   * Load the existing test json file
+   * Load the test json file
    */
   @Test
   public void testLoadExistingJsonFile() throws Exception {
-    Set<DatanodeAdminProperties> all =
-        CombinedHostsFileReader.readFile(EXISTING_FILE.getAbsolutePath());
-    assertEquals(7, all.size());
+    DatanodeAdminProperties[] all =
+        CombinedHostsFileReader.readFile(jsonFile.getAbsolutePath());
+    assertEquals(7, all.length);
   }
 
   /*
@@ -70,11 +80,11 @@ public class TestCombinedHostsFileReader {
    */
   @Test
   public void testEmptyCombinedHostsFileReader() throws Exception {
-    FileWriter hosts = new FileWriter(NEW_FILE);
+    FileWriter hosts = new FileWriter(newFile);
     hosts.write("");
     hosts.close();
-    Set<DatanodeAdminProperties> all =
-        CombinedHostsFileReader.readFile(NEW_FILE.getAbsolutePath());
-    assertEquals(0, all.size());
+    DatanodeAdminProperties[] all =
+        CombinedHostsFileReader.readFile(newFile.getAbsolutePath());
+    assertEquals(0, all.length);
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/resources/dfs.hosts.json

@@ -1,7 +1,9 @@
-{"hostName": "host1"}
-{"hostName": "host2", "upgradeDomain": "ud0"}
-{"hostName": "host3", "adminState": "DECOMMISSIONED"}
-{"hostName": "host4", "upgradeDomain": "ud2", "adminState": "DECOMMISSIONED"}
-{"hostName": "host5", "port": 8090}
-{"hostName": "host6", "adminState": "IN_MAINTENANCE"}
-{"hostName": "host7", "adminState": "IN_MAINTENANCE", "maintenanceExpireTimeInMS": "112233"}
+[
+  {"hostName": "host1"},
+  {"hostName": "host2", "upgradeDomain": "ud0"},
+  {"hostName": "host3", "adminState": "DECOMMISSIONED"},
+  {"hostName": "host4", "upgradeDomain": "ud2", "adminState": "DECOMMISSIONED"},
+  {"hostName": "host5", "port": 8090},
+  {"hostName": "host6", "adminState": "IN_MAINTENANCE"},
+  {"hostName": "host7", "adminState": "IN_MAINTENANCE", "maintenanceExpireTimeInMS": "112233"}
+]

hadoop-hdfs-project/hadoop-hdfs/src/test/resources/legacy.dfs.hosts.json

@@ -0,0 +1,7 @@
+{"hostName": "host1"}
+{"hostName": "host2", "upgradeDomain": "ud0"}
+{"hostName": "host3", "adminState": "DECOMMISSIONED"}
+{"hostName": "host4", "upgradeDomain": "ud2", "adminState": "DECOMMISSIONED"}
+{"hostName": "host5", "port": 8090}
+{"hostName": "host6", "adminState": "IN_MAINTENANCE"}
+{"hostName": "host7", "adminState": "IN_MAINTENANCE", "maintenanceExpireTimeInMS": "112233"}