HDFS-6874. Add GETFILEBLOCKLOCATIONS operation to HttpFS (#4750)

Co-authored-by: Ashutosh Gupta <ashugpt@amazon.com>

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

@@ -18,6 +18,7 @@
 
 package org.apache.hadoop.hdfs;
 
+import org.apache.hadoop.hdfs.protocol.LocatedBlocks;
 import org.apache.hadoop.security.AccessControlException;
 import org.apache.hadoop.classification.VisibleForTesting;
 import org.apache.hadoop.util.Preconditions;
@@ -3898,4 +3899,36 @@ public class DistributedFileSystem extends FileSystem
     return dfs.slowDatanodeReport();
   }
 
+  /**
+   * Returns LocatedBlocks of the corresponding HDFS file p from offset start
+   * for length len.
+   * This is similar to {@link #getFileBlockLocations(Path, long, long)} except
+   * that it returns LocatedBlocks rather than BlockLocation array.
+   * @param p path representing the file of interest.
+   * @param start offset
+   * @param len length
+   * @return a LocatedBlocks object
+   * @throws IOException
+   */
+  public LocatedBlocks getLocatedBlocks(Path p, long start, long len)
+      throws IOException {
+    final Path absF = fixRelativePart(p);
+    return new FileSystemLinkResolver<LocatedBlocks>() {
+      @Override
+      public LocatedBlocks doCall(final Path p) throws IOException {
+        return dfs.getLocatedBlocks(getPathName(p), start, len);
+      }
+      @Override
+      public LocatedBlocks next(final FileSystem fs, final Path p)
+          throws IOException {
+        if (fs instanceof DistributedFileSystem) {
+          DistributedFileSystem myDfs = (DistributedFileSystem)fs;
+          return myDfs.getLocatedBlocks(p, start, len);
+        }
+        throw new UnsupportedOperationException("Cannot getLocatedBlocks " +
+            "through a symlink to a non-DistributedFileSystem: " + fs + " -> "+
+            p);
+      }
+    }.resolve(this, absF);
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/JsonUtilClient.java

@@ -19,6 +19,9 @@ package org.apache.hadoop.hdfs.web;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.ObjectReader;
+
+import org.apache.hadoop.classification.VisibleForTesting;
+import org.apache.hadoop.fs.BlockLocation;
 import org.apache.hadoop.util.Preconditions;
 import org.apache.hadoop.thirdparty.com.google.common.collect.Maps;
 import org.apache.hadoop.fs.ContentSummary;
@@ -965,4 +968,53 @@ public class JsonUtilClient {
                 SnapshotStatus.getParentPath(fullPath)));
     return snapshotStatus;
   }
+
+  @VisibleForTesting
+  public static BlockLocation[] toBlockLocationArray(Map<?, ?> json)
+      throws IOException {
+    final Map<?, ?> rootmap =
+        (Map<?, ?>) json.get(BlockLocation.class.getSimpleName() + "s");
+    final List<?> array =
+        JsonUtilClient.getList(rootmap, BlockLocation.class.getSimpleName());
+    Preconditions.checkNotNull(array);
+    final BlockLocation[] locations = new BlockLocation[array.size()];
+    int i = 0;
+    for (Object object : array) {
+      final Map<?, ?> m = (Map<?, ?>) object;
+      locations[i++] = JsonUtilClient.toBlockLocation(m);
+    }
+    return locations;
+  }
+
+  /** Convert a Json map to BlockLocation. **/
+  private static BlockLocation toBlockLocation(Map<?, ?> m) throws IOException {
+    if (m == null) {
+      return null;
+    }
+    long length = ((Number) m.get("length")).longValue();
+    long offset = ((Number) m.get("offset")).longValue();
+    boolean corrupt = Boolean.getBoolean(m.get("corrupt").toString());
+    String[] storageIds = toStringArray(getList(m, "storageIds"));
+    String[] cachedHosts = toStringArray(getList(m, "cachedHosts"));
+    String[] hosts = toStringArray(getList(m, "hosts"));
+    String[] names = toStringArray(getList(m, "names"));
+    String[] topologyPaths = toStringArray(getList(m, "topologyPaths"));
+    StorageType[] storageTypes = toStorageTypeArray(getList(m, "storageTypes"));
+    return new BlockLocation(names, hosts, cachedHosts, topologyPaths,
+        storageIds, storageTypes, offset, length, corrupt);
+  }
+
+  @VisibleForTesting
+  static String[] toStringArray(List<?> list) {
+    if (list == null) {
+      return null;
+    } else {
+      final String[] array = new String[list.size()];
+      int i = 0;
+      for (Object object : list) {
+        array[i++] = object.toString();
+      }
+      return array;
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/WebHdfsFileSystem.java

@@ -183,6 +183,8 @@ public class WebHdfsFileSystem extends FileSystem
   private KeyProvider testProvider;
   private boolean isTLSKrb;
 
+  private boolean isServerHCFSCompatible = true;
+
   /**
    * Return the protocol scheme for the FileSystem.
    *
@@ -1882,18 +1884,51 @@ public class WebHdfsFileSystem extends FileSystem
   }
 
   @Override
-  public BlockLocation[] getFileBlockLocations(final Path p,
-      final long offset, final long length) throws IOException {
+  public BlockLocation[] getFileBlockLocations(final Path p, final long offset,
+      final long length) throws IOException {
     statistics.incrementReadOps(1);
     storageStatistics.incrementOpCounter(OpType.GET_FILE_BLOCK_LOCATIONS);
+    BlockLocation[] locations;
+    try {
+      if (isServerHCFSCompatible) {
+        locations = getFileBlockLocations(GetOpParam.Op.GETFILEBLOCKLOCATIONS, p, offset, length);
+      } else {
+        locations = getFileBlockLocations(GetOpParam.Op.GET_BLOCK_LOCATIONS, p, offset, length);
+      }
+    } catch (RemoteException e) {
+      // parsing the exception is needed only if the client thinks the service is compatible
+      if (isServerHCFSCompatible && isGetFileBlockLocationsException(e)) {
+        LOG.warn("Server does not appear to support GETFILEBLOCKLOCATIONS." +
+                "Fallback to the old GET_BLOCK_LOCATIONS. Exception: {}",
+            e.getMessage());
+        isServerHCFSCompatible = false;
+        locations = getFileBlockLocations(GetOpParam.Op.GET_BLOCK_LOCATIONS, p, offset, length);
+      } else {
+        throw e;
+      }
+    }
+    return locations;
+  }
 
-    final HttpOpParam.Op op = GetOpParam.Op.GET_BLOCK_LOCATIONS;
-    return new FsPathResponseRunner<BlockLocation[]>(op, p,
+  private boolean isGetFileBlockLocationsException(RemoteException e) {
+    return e.getMessage() != null && e.getMessage().contains("Invalid value for webhdfs parameter")
+        && e.getMessage().contains(GetOpParam.Op.GETFILEBLOCKLOCATIONS.toString());
+  }
+
+  private BlockLocation[] getFileBlockLocations(final GetOpParam.Op operation,
+      final Path p, final long offset, final long length) throws IOException {
+    return new FsPathResponseRunner<BlockLocation[]>(operation, p,
         new OffsetParam(offset), new LengthParam(length)) {
       @Override
-      BlockLocation[] decodeResponse(Map<?,?> json) throws IOException {
-        return DFSUtilClient.locatedBlocks2Locations(
-            JsonUtilClient.toLocatedBlocks(json));
+      BlockLocation[] decodeResponse(Map<?, ?> json) throws IOException {
+        switch (operation) {
+        case GETFILEBLOCKLOCATIONS:
+          return JsonUtilClient.toBlockLocationArray(json);
+        case GET_BLOCK_LOCATIONS:
+          return DFSUtilClient.locatedBlocks2Locations(JsonUtilClient.toLocatedBlocks(json));
+        default:
+          throw new IOException("Unknown operation " + operation.name());
+        }
       }
     }.run();
   }

hadoop-hdfs-project/hadoop-hdfs-httpfs/pom.xml

@@ -199,6 +199,16 @@
       <artifactId>bcprov-jdk15on</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>com.squareup.okhttp3</groupId>
+      <artifactId>mockwebserver</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.squareup.okhttp3</groupId>
+      <artifactId>okhttp</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <build>

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/client/HttpFSFileSystem.java

@@ -24,8 +24,12 @@ import java.util.EnumSet;
 import java.util.List;
 
 import org.apache.hadoop.thirdparty.com.google.common.base.Charsets;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.type.MapType;
 import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.VisibleForTesting;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.BlockLocation;
 import org.apache.hadoop.fs.CommonPathCapabilities;
 import org.apache.hadoop.fs.ContentSummary;
 import org.apache.hadoop.fs.DelegationTokenRenewer;
@@ -140,6 +144,8 @@ public class HttpFSFileSystem extends FileSystem
   public static final String SNAPSHOT_DIFF_INDEX = "snapshotdiffindex";
   public static final String FSACTION_MODE_PARAM = "fsaction";
   public static final String EC_POLICY_NAME_PARAM = "ecpolicy";
+  public static final String OFFSET_PARAM = "offset";
+  public static final String LENGTH_PARAM = "length";
 
   public static final Short DEFAULT_PERMISSION = 0755;
   public static final String ACLSPEC_DEFAULT = "";
@@ -239,6 +245,7 @@ public class HttpFSFileSystem extends FileSystem
 
   public static final String STORAGE_POLICIES_JSON = "BlockStoragePolicies";
   public static final String STORAGE_POLICY_JSON = "BlockStoragePolicy";
+  public static final String BLOCK_LOCATIONS_JSON = "BlockLocations";
 
   public static final int HTTP_TEMPORARY_REDIRECT = 307;
 
@@ -269,7 +276,8 @@ public class HttpFSFileSystem extends FileSystem
     GETSNAPSHOTTABLEDIRECTORYLIST(HTTP_GET), GETSNAPSHOTLIST(HTTP_GET),
     GETSERVERDEFAULTS(HTTP_GET),
     CHECKACCESS(HTTP_GET), SETECPOLICY(HTTP_PUT), GETECPOLICY(HTTP_GET), UNSETECPOLICY(
-        HTTP_POST), SATISFYSTORAGEPOLICY(HTTP_PUT), GETSNAPSHOTDIFFLISTING(HTTP_GET);
+        HTTP_POST), SATISFYSTORAGEPOLICY(HTTP_PUT), GETSNAPSHOTDIFFLISTING(HTTP_GET),
+    GET_BLOCK_LOCATIONS(HTTP_GET);
 
     private String httpMethod;
 
@@ -1710,4 +1718,41 @@ public class HttpFSFileSystem extends FileSystem
         Operation.SATISFYSTORAGEPOLICY.getMethod(), params, path, true);
     HttpExceptionUtils.validateResponse(conn, HttpURLConnection.HTTP_OK);
   }
-}
+
+  @Override
+  public BlockLocation[] getFileBlockLocations(Path path, long start, long len)
+      throws IOException {
+    Map<String, String> params = new HashMap<>();
+    params.put(OP_PARAM, Operation.GETFILEBLOCKLOCATIONS.toString());
+    params.put(OFFSET_PARAM, Long.toString(start));
+    params.put(LENGTH_PARAM, Long.toString(len));
+    HttpURLConnection conn = getConnection(
+        Operation.GETFILEBLOCKLOCATIONS.getMethod(), params, path, true);
+    HttpExceptionUtils.validateResponse(conn, HttpURLConnection.HTTP_OK);
+    JSONObject json = (JSONObject) HttpFSUtils.jsonParse(conn);
+    return toBlockLocations(json);
+  }
+
+  @Override
+  public BlockLocation[] getFileBlockLocations(final FileStatus status,
+      final long offset, final long length) throws IOException {
+    if (status == null) {
+      return null;
+    }
+    return getFileBlockLocations(status.getPath(), offset, length);
+  }
+
+  @VisibleForTesting
+  static BlockLocation[] toBlockLocations(JSONObject json) throws IOException {
+    ObjectMapper mapper = new ObjectMapper();
+    MapType subType = mapper.getTypeFactory().constructMapType(Map.class,
+        String.class, BlockLocation[].class);
+    MapType rootType = mapper.getTypeFactory().constructMapType(Map.class,
+        mapper.constructType(String.class), mapper.constructType(subType));
+
+    Map<String, Map<String, BlockLocation[]>> jsonMap =
+        mapper.readValue(json.toJSONString(), rootType);
+    Map<String, BlockLocation[]> locationMap = jsonMap.get(BLOCK_LOCATIONS_JSON);
+    return locationMap.get(BlockLocation.class.getSimpleName());
+  }
+}

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/FSOperations.java

@@ -19,6 +19,7 @@ package org.apache.hadoop.fs.http.server;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.BlockLocation;
 import org.apache.hadoop.fs.BlockStoragePolicySpi;
 import org.apache.hadoop.fs.ContentSummary;
 import org.apache.hadoop.fs.FileChecksum;
@@ -44,6 +45,7 @@ import org.apache.hadoop.hdfs.protocol.BlockStoragePolicy;
 import org.apache.hadoop.hdfs.protocol.ErasureCodingPolicy;
 import org.apache.hadoop.hdfs.protocol.HdfsConstants;
 import org.apache.hadoop.hdfs.protocol.HdfsFileStatus;
+import org.apache.hadoop.hdfs.protocol.LocatedBlocks;
 import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport;
 import org.apache.hadoop.hdfs.protocol.SnapshotDiffReportListing;
 import org.apache.hadoop.hdfs.protocol.SnapshottableDirectoryStatus;
@@ -2192,4 +2194,75 @@ public final class FSOperations {
       return null;
     }
   }
+
+  /**
+   * Executor that performs a getFileBlockLocations operation.
+   */
+
+  @InterfaceAudience.Private
+  @SuppressWarnings("rawtypes")
+  public static class FSFileBlockLocations implements FileSystemAccess.FileSystemExecutor<Map> {
+    final private Path path;
+    final private long offsetValue;
+    final private long lengthValue;
+
+    /**
+     * Creates a file-block-locations executor.
+     *
+     * @param path the path to retrieve the location
+     * @param offsetValue offset into the given file
+     * @param lengthValue length for which to get locations for
+     */
+    public FSFileBlockLocations(String path, long offsetValue, long lengthValue) {
+      this.path = new Path(path);
+      this.offsetValue = offsetValue;
+      this.lengthValue = lengthValue;
+    }
+
+    @Override
+    public Map execute(FileSystem fs) throws IOException {
+      BlockLocation[] locations = fs.getFileBlockLocations(this.path,
+          this.offsetValue, this.lengthValue);
+      return JsonUtil.toJsonMap(locations);
+    }
+  }
+
+  /**
+   * Executor that performs a getFileBlockLocations operation for legacy
+   * clients that supports only GET_BLOCK_LOCATIONS.
+   */
+
+  @InterfaceAudience.Private
+  @SuppressWarnings("rawtypes")
+  public static class FSFileBlockLocationsLegacy
+      implements FileSystemAccess.FileSystemExecutor<Map> {
+    final private Path path;
+    final private long offsetValue;
+    final private long lengthValue;
+
+    /**
+     * Creates a file-block-locations executor.
+     *
+     * @param path the path to retrieve the location
+     * @param offsetValue offset into the given file
+     * @param lengthValue length for which to get locations for
+     */
+    public FSFileBlockLocationsLegacy(String path, long offsetValue, long lengthValue) {
+      this.path = new Path(path);
+      this.offsetValue = offsetValue;
+      this.lengthValue = lengthValue;
+    }
+
+    @Override
+    public Map execute(FileSystem fs) throws IOException {
+      if (fs instanceof DistributedFileSystem) {
+        DistributedFileSystem dfs = (DistributedFileSystem)fs;
+        LocatedBlocks locations = dfs.getLocatedBlocks(
+            this.path, this.offsetValue, this.lengthValue);
+        return JsonUtil.toJsonMap(locations);
+      }
+      throw new IOException("Unable to support FSFileBlockLocationsLegacy " +
+          "because the file system is not DistributedFileSystem.");
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/HttpFSParametersProvider.java

@@ -60,7 +60,8 @@ public class HttpFSParametersProvider extends ParametersProvider {
     PARAMS_DEF.put(Operation.GETQUOTAUSAGE, new Class[]{});
     PARAMS_DEF.put(Operation.GETFILECHECKSUM,
         new Class[]{NoRedirectParam.class});
-    PARAMS_DEF.put(Operation.GETFILEBLOCKLOCATIONS, new Class[]{});
+    PARAMS_DEF.put(Operation.GETFILEBLOCKLOCATIONS,
+        new Class[] {OffsetParam.class, LenParam.class});
     PARAMS_DEF.put(Operation.GETACLSTATUS, new Class[]{});
     PARAMS_DEF.put(Operation.GETTRASHROOT, new Class[]{});
     PARAMS_DEF.put(Operation.INSTRUMENTATION, new Class[]{});
@@ -127,6 +128,7 @@ public class HttpFSParametersProvider extends ParametersProvider {
     PARAMS_DEF.put(Operation.GETECPOLICY, new Class[] {});
     PARAMS_DEF.put(Operation.UNSETECPOLICY, new Class[] {});
     PARAMS_DEF.put(Operation.SATISFYSTORAGEPOLICY, new Class[] {});
+    PARAMS_DEF.put(Operation.GET_BLOCK_LOCATIONS, new Class[] {OffsetParam.class, LenParam.class});
   }
 
   public HttpFSParametersProvider() {

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/HttpFSServer.java

@@ -370,7 +370,23 @@ public class HttpFSServer {
       break;
     }
     case GETFILEBLOCKLOCATIONS: {
-      response = Response.status(Response.Status.BAD_REQUEST).build();
+      long offset = 0;
+      long len = Long.MAX_VALUE;
+      Long offsetParam = params.get(OffsetParam.NAME, OffsetParam.class);
+      Long lenParam = params.get(LenParam.NAME, LenParam.class);
+      AUDIT_LOG.info("[{}] offset [{}] len [{}]", path, offsetParam, lenParam);
+      if (offsetParam != null && offsetParam > 0) {
+        offset = offsetParam;
+      }
+      if (lenParam != null && lenParam > 0) {
+        len = lenParam;
+      }
+      FSOperations.FSFileBlockLocations command =
+          new FSOperations.FSFileBlockLocations(path, offset, len);
+      @SuppressWarnings("rawtypes")
+      Map locations = fsExecute(user, command);
+      final String json = JsonUtil.toJsonString("BlockLocations", locations);
+      response = Response.ok(json).type(MediaType.APPLICATION_JSON).build();
       break;
     }
     case GETACLSTATUS: {
@@ -510,6 +526,26 @@ public class HttpFSServer {
       response = Response.ok(js).type(MediaType.APPLICATION_JSON).build();
       break;
     }
+    case GET_BLOCK_LOCATIONS: {
+      long offset = 0;
+      long len = Long.MAX_VALUE;
+      Long offsetParam = params.get(OffsetParam.NAME, OffsetParam.class);
+      Long lenParam = params.get(LenParam.NAME, LenParam.class);
+      AUDIT_LOG.info("[{}] offset [{}] len [{}]", path, offsetParam, lenParam);
+      if (offsetParam != null && offsetParam > 0) {
+        offset = offsetParam;
+      }
+      if (lenParam != null && lenParam > 0) {
+        len = lenParam;
+      }
+      FSOperations.FSFileBlockLocationsLegacy command =
+          new FSOperations.FSFileBlockLocationsLegacy(path, offset, len);
+      @SuppressWarnings("rawtypes")
+      Map locations = fsExecute(user, command);
+      final String json = JsonUtil.toJsonString("LocatedBlocks", locations);
+      response = Response.ok(json).type(MediaType.APPLICATION_JSON).build();
+      break;
+    }
     default: {
       throw new IOException(
           MessageFormat.format("Invalid HTTP GET operation [{0}]", op.value()));

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/fs/http/client/BaseTestHttpFSWith.java

@@ -19,6 +19,7 @@
 package org.apache.hadoop.fs.http.client;
 
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.BlockLocation;
 import org.apache.hadoop.fs.BlockStoragePolicySpi;
 import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
 import org.apache.hadoop.fs.ContentSummary;
@@ -73,6 +74,10 @@ import org.apache.hadoop.test.TestHdfsHelper;
 import org.apache.hadoop.test.TestJetty;
 import org.apache.hadoop.test.TestJettyHelper;
 import org.apache.hadoop.util.Lists;
+
+import org.json.simple.JSONObject;
+import org.json.simple.parser.ContainerFactory;
+import org.json.simple.parser.JSONParser;
 import org.junit.Assert;
 import org.junit.Assume;
 import org.junit.Test;
@@ -101,11 +106,11 @@ import java.util.regex.Pattern;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
 @RunWith(value = Parameterized.class)
 public abstract class BaseTestHttpFSWith extends HFSTestCase {
-
   protected abstract Path getProxiedFSTestDir();
 
   protected abstract String getProxiedFSURI();
@@ -191,7 +196,7 @@ public abstract class BaseTestHttpFSWith extends HFSTestCase {
 
   protected void testGet() throws Exception {
     FileSystem fs = getHttpFSFileSystem();
-    Assert.assertNotNull(fs);
+    assertNotNull(fs);
     URI uri = new URI(getScheme() + "://" +
                       TestJettyHelper.getJettyURL().toURI().getAuthority());
     assertEquals(fs.getUri(), uri);
@@ -1201,7 +1206,7 @@ public abstract class BaseTestHttpFSWith extends HFSTestCase {
     ALLOW_SNAPSHOT, DISALLOW_SNAPSHOT, DISALLOW_SNAPSHOT_EXCEPTION,
     FILE_STATUS_ATTR, GET_SNAPSHOT_DIFF, GET_SNAPSHOTTABLE_DIRECTORY_LIST,
     GET_SNAPSHOT_LIST, GET_SERVERDEFAULTS, CHECKACCESS, SETECPOLICY,
-    SATISFYSTORAGEPOLICY, GET_SNAPSHOT_DIFF_LISTING
+    SATISFYSTORAGEPOLICY, GET_SNAPSHOT_DIFF_LISTING, GETFILEBLOCKLOCATIONS
   }
 
   private void operation(Operation op) throws Exception {
@@ -1341,6 +1346,9 @@ public abstract class BaseTestHttpFSWith extends HFSTestCase {
     case GET_SNAPSHOT_DIFF_LISTING:
       testGetSnapshotDiffListing();
       break;
+    case GETFILEBLOCKLOCATIONS:
+      testGetFileBlockLocations();
+      break;
     }
 
   }
@@ -1959,6 +1967,37 @@ public abstract class BaseTestHttpFSWith extends HFSTestCase {
     }
   }
 
+  private void testGetFileBlockLocations() throws Exception {
+    BlockLocation[] blockLocations;
+    Path testFile;
+    if (!this.isLocalFS()) {
+      FileSystem fs = this.getHttpFSFileSystem();
+      testFile = new Path(getProxiedFSTestDir(), "singleBlock.txt");
+      DFSTestUtil.createFile(fs, testFile, 1, (short) 1, 0L);
+      if (fs instanceof HttpFSFileSystem) {
+        HttpFSFileSystem httpFS = (HttpFSFileSystem) fs;
+        blockLocations = httpFS.getFileBlockLocations(testFile, 0, 1);
+        assertNotNull(blockLocations);
+
+        // verify HttpFSFileSystem.toBlockLocations()
+        String jsonString = JsonUtil.toJsonString(blockLocations);
+        JSONParser parser = new JSONParser();
+        JSONObject jsonObject = (JSONObject) parser.parse(jsonString, (ContainerFactory) null);
+        BlockLocation[] deserializedLocation = HttpFSFileSystem.toBlockLocations(jsonObject);
+        assertEquals(blockLocations.length, deserializedLocation.length);
+        for (int i = 0; i < blockLocations.length; i++) {
+          assertEquals(blockLocations[i].toString(), deserializedLocation[i].toString());
+        }
+      } else if (fs instanceof WebHdfsFileSystem) {
+        WebHdfsFileSystem webHdfsFileSystem = (WebHdfsFileSystem) fs;
+        blockLocations = webHdfsFileSystem.getFileBlockLocations(testFile, 0, 1);
+        assertNotNull(blockLocations);
+      } else {
+        Assert.fail(fs.getClass().getSimpleName() + " doesn't support access");
+      }
+    }
+  }
+
   private void testGetSnapshotDiffListing() throws Exception {
     if (!this.isLocalFS()) {
       // Create a directory with snapshot allowed

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/fs/http/server/TestHttpFSServer.java

@@ -36,12 +36,14 @@ import org.apache.hadoop.hdfs.protocol.SnapshotStatus;
 import org.apache.hadoop.hdfs.protocol.SystemErasureCodingPolicies;
 import org.apache.hadoop.hdfs.server.common.HdfsServerConstants;
 import org.apache.hadoop.hdfs.web.JsonUtil;
+import org.apache.hadoop.hdfs.web.JsonUtilClient;
 import org.apache.hadoop.lib.service.FileSystemAccess;
 import org.apache.hadoop.security.authentication.util.SignerSecretProvider;
 import org.apache.hadoop.security.authentication.util.StringSignerSecretProviderCreator;
 import org.apache.hadoop.security.token.delegation.AbstractDelegationTokenIdentifier;
 import org.apache.hadoop.security.token.delegation.web.DelegationTokenAuthenticator;
 import org.apache.hadoop.security.token.delegation.web.KerberosDelegationTokenAuthenticationHandler;
+import org.apache.hadoop.util.JsonSerialization;
 import org.json.simple.JSONArray;
 import org.junit.Assert;
 
@@ -70,6 +72,7 @@ import java.util.Set;
 
 import org.apache.commons.io.IOUtils;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.BlockLocation;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.FsServerDefaults;
 import org.apache.hadoop.fs.Path;
@@ -2003,4 +2006,38 @@ public class TestHttpFSServer extends HFSTestCase {
         () -> HttpFSUtils.jsonParse(conn));
     conn.disconnect();
   }
+
+  @Test
+  @TestDir
+  @TestJetty
+  @TestHdfs
+  public void testGetFileBlockLocations() throws Exception {
+    createHttpFSServer(false, false);
+    // Create a test directory
+    String pathStr = "/tmp/tmp-get-block-location-test";
+    createDirWithHttp(pathStr, "700", null);
+
+    Path path = new Path(pathStr);
+    DistributedFileSystem dfs = (DistributedFileSystem) FileSystem
+        .get(path.toUri(), TestHdfsHelper.getHdfsConf());
+
+    String file1 = pathStr + "/file1";
+    createWithHttp(file1, null);
+    HttpURLConnection conn = sendRequestToHttpFSServer(file1,
+        "GETFILEBLOCKLOCATIONS", "length=10&offset10");
+    Assert.assertEquals(HttpURLConnection.HTTP_OK, conn.getResponseCode());
+    BlockLocation[] locations1 = dfs.getFileBlockLocations(new Path(file1), 0, 1);
+    Assert.assertNotNull(locations1);
+
+    Map<?, ?> jsonMap = JsonSerialization.mapReader().readValue(conn.getInputStream());
+
+    BlockLocation[] httpfsBlockLocations = JsonUtilClient.toBlockLocationArray(jsonMap);
+
+    assertEquals(locations1.length, httpfsBlockLocations.length);
+    for (int i = 0; i < locations1.length; i++) {
+      assertEquals(locations1[i].toString(), httpfsBlockLocations[i].toString());
+    }
+
+    conn.getInputStream().close();
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/web/JsonUtil.java

@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.hdfs.web;
 
+import org.apache.hadoop.classification.VisibleForTesting;
 import org.apache.hadoop.fs.BlockLocation;
 import org.apache.hadoop.fs.ContentSummary;
 import org.apache.hadoop.fs.FileChecksum;
@@ -335,6 +336,17 @@ public class JsonUtil {
       return null;
     }
 
+    final Map<String, Object> m = toJsonMap(locatedblocks);
+    return toJsonString(LocatedBlocks.class, m);
+  }
+
+  /** Convert LocatedBlocks to a Map. */
+  public static Map<String, Object> toJsonMap(final LocatedBlocks locatedblocks)
+      throws IOException {
+    if (locatedblocks == null) {
+      return null;
+    }
+
     final Map<String, Object> m = new TreeMap<String, Object>();
     m.put("fileLength", locatedblocks.getFileLength());
     m.put("isUnderConstruction", locatedblocks.isUnderConstruction());
@@ -342,7 +354,7 @@ public class JsonUtil {
     m.put("locatedBlocks", toJsonArray(locatedblocks.getLocatedBlocks()));
     m.put("lastLocatedBlock", toJsonMap(locatedblocks.getLastLocatedBlock()));
     m.put("isLastBlockComplete", locatedblocks.isLastBlockComplete());
-    return toJsonString(LocatedBlocks.class, m);
+    return m;
   }
 
   /** Convert a ContentSummary to a Json string. */
@@ -676,7 +688,8 @@ public class JsonUtil {
     return m;
   }
 
-  private static Map<String, Object> toJsonMap(
+  @VisibleForTesting
+  static Map<String, Object> toJsonMap(
       final BlockLocation blockLocation) throws IOException {
     if (blockLocation == null) {
       return null;
@@ -696,15 +709,20 @@ public class JsonUtil {
 
   public static String toJsonString(BlockLocation[] locations)
       throws IOException {
+    return toJsonString("BlockLocations", JsonUtil.toJsonMap(locations));
+  }
+
+  public static Map<String, Object> toJsonMap(BlockLocation[] locations)
+      throws IOException {
     if (locations == null) {
       return null;
     }
     final Map<String, Object> m = new HashMap<>();
     Object[] blockLocations = new Object[locations.length];
-    for(int i=0; i<locations.length; i++) {
+    for (int i = 0; i < locations.length; i++) {
       blockLocations[i] = toJsonMap(locations[i]);
     }
     m.put(BlockLocation.class.getSimpleName(), blockLocations);
-    return toJsonString("BlockLocations", m);
+    return m;
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/web/TestJsonUtilClient.java

@@ -0,0 +1,68 @@
+/**
+ * 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.web;
+
+import org.apache.hadoop.fs.BlockLocation;
+import org.apache.hadoop.fs.StorageType;
+import org.apache.hadoop.util.JsonSerialization;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+public class TestJsonUtilClient {
+  @Test
+  public void testToStringArray() {
+    List<String> strList = new ArrayList<String>(Arrays.asList("aaa", "bbb", "ccc"));
+
+    String[] strArr = JsonUtilClient.toStringArray(strList);
+    assertEquals("Expected 3 items in the array", 3, strArr.length);
+    assertEquals("aaa", strArr[0]);
+    assertEquals("bbb", strArr[1]);
+    assertEquals("ccc", strArr[2]);
+  }
+
+  @Test
+  public void testToBlockLocationArray() throws Exception {
+    BlockLocation blockLocation = new BlockLocation(
+        new String[] {"127.0.0.1:62870"},
+        new String[] {"127.0.0.1"},
+        null,
+        new String[] {"/default-rack/127.0.0.1:62870"},
+        null,
+        new StorageType[] {StorageType.DISK},
+        0, 1, false);
+
+    Map<String, Object> blockLocationsMap =
+        JsonUtil.toJsonMap(new BlockLocation[] {blockLocation});
+    String json = JsonUtil.toJsonString("BlockLocations", blockLocationsMap);
+    assertNotNull(json);
+    Map<?, ?> jsonMap = JsonSerialization.mapReader().readValue(json);
+
+    BlockLocation[] deserializedBlockLocations =
+        JsonUtilClient.toBlockLocationArray(jsonMap);
+    assertEquals(1, deserializedBlockLocations.length);
+    assertEquals(blockLocation.toString(),
+        deserializedBlockLocations[0].toString());
+  }
+}