HBASE-22377 Provide API to check the existence of a namespace which does not require ADMIN permissions (#225)

Signed-off-by: Xu Cang <xucang@apache.org>

hbase-client/src/main/java/org/apache/hadoop/hbase/client/Admin.java

@@ -112,7 +112,7 @@ public interface Admin extends Abortable, Closeable {
   /**
    * @param tableName Table to check.
    * @return <code>true</code> if table exists already.
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    */
   boolean tableExists(TableName tableName) throws IOException;
 
@@ -486,7 +486,7 @@ public interface Admin extends Abortable, Closeable {
    * Get all the online regions on a region server.
    *
    * @return List of {@link RegionInfo}
-   * @throws java.io.IOException
+   * @throws IOException if a remote or network exception occurs
    */
   List<RegionInfo> getRegions(ServerName serverName) throws IOException;
 
@@ -1130,8 +1130,18 @@ public interface Admin extends Abortable, Closeable {
       throws NamespaceNotFoundException, IOException;
 
   /**
-   * List available namespace descriptors.
+   * List available namespaces
+   *
+   * @return List of namespace names
+   * @throws IOException if a remote or network exception occurs
+   */
+  String[] listNamespaces() throws IOException;
+
+  /**
+   * List available namespace descriptors
+   *
    * @return List of descriptors
+   * @throws IOException if a remote or network exception occurs
    */
   NamespaceDescriptor[] listNamespaceDescriptors() throws IOException;
 
@@ -1139,6 +1149,7 @@ public interface Admin extends Abortable, Closeable {
    * Get list of table descriptors by namespace.
    * @param name namespace name
    * @return returns a list of TableDescriptors
+   * @throws IOException if a remote or network exception occurs
    */
   List<TableDescriptor> listTableDescriptorsByNamespace(byte[] name) throws IOException;
 
@@ -1146,6 +1157,7 @@ public interface Admin extends Abortable, Closeable {
    * Get list of table names by namespace.
    * @param name namespace name
    * @return The list of table names in the namespace
+   * @throws IOException if a remote or network exception occurs
    */
   TableName[] listTableNamesByNamespace(String name) throws IOException;
 
@@ -1154,6 +1166,7 @@ public interface Admin extends Abortable, Closeable {
    *
    * @param tableName the name of the table
    * @return List of {@link RegionInfo}.
+   * @throws IOException if a remote or network exception occurs
    */
   List<RegionInfo> getRegions(TableName tableName) throws IOException;
 
@@ -1178,7 +1191,7 @@ public interface Admin extends Abortable, Closeable {
    * @param mayInterruptIfRunning if the proc completed at least one step, should it be aborted?
    * @return <code>true</code> if aborted, <code>false</code> if procedure already completed or does
    *         not exist
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    * @deprecated Since 2.1.1 -- to be removed.
    */
   @Deprecated
@@ -1198,7 +1211,7 @@ public interface Admin extends Abortable, Closeable {
    * @param procId ID of the procedure to abort
    * @param mayInterruptIfRunning if the proc completed at least one step, should it be aborted?
    * @return <code>true</code> if aborted, <code>false</code> if procedure already completed or does not exist
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    * @deprecated Since 2.1.1 -- to be removed.
    */
   @Deprecated
@@ -1208,7 +1221,7 @@ public interface Admin extends Abortable, Closeable {
   /**
    * Get procedures.
    * @return procedure list in JSON
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    */
   String getProcedures() throws IOException;
 

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncAdmin.java

@@ -270,6 +270,12 @@ public interface AsyncAdmin {
    */
   CompletableFuture<NamespaceDescriptor> getNamespaceDescriptor(String name);
 
+  /**
+   * List available namespaces
+   * @return List of namespaces wrapped by a {@link CompletableFuture}.
+   */
+  CompletableFuture<List<String>> listNamespaces();
+
   /**
    * List available namespace descriptors
    * @return List of descriptors wrapped by a {@link CompletableFuture}.

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncHBaseAdmin.java

@@ -214,6 +214,11 @@ class AsyncHBaseAdmin implements AsyncAdmin {
     return wrap(rawAdmin.getNamespaceDescriptor(name));
   }
 
+  @Override
+  public CompletableFuture<List<String>> listNamespaces() {
+    return wrap(rawAdmin.listNamespaces());
+  }
+
   @Override
   public CompletableFuture<List<NamespaceDescriptor>> listNamespaceDescriptors() {
     return wrap(rawAdmin.listNamespaceDescriptors());

hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionImplementation.java

@@ -1561,6 +1561,13 @@ class ConnectionImplementation implements ClusterConnection, Closeable {
         return stub.deleteNamespace(controller, request);
       }
 
+      @Override
+      public MasterProtos.ListNamespacesResponse listNamespaces(
+          RpcController controller,
+          MasterProtos.ListNamespacesRequest request) throws ServiceException {
+        return stub.listNamespaces(controller, request);
+      }
+
       @Override
       public MasterProtos.GetNamespaceDescriptorResponse getNamespaceDescriptor(
           RpcController controller,

hbase-client/src/main/java/org/apache/hadoop/hbase/client/HBaseAdmin.java

@@ -182,6 +182,7 @@ import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.IsSnapshot
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.IsSnapshotDoneResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListDecommissionedRegionServersRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespaceDescriptorsRequest;
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespacesRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableDescriptorsByNamespaceRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableNamesByNamespaceRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.MajorCompactionTimestampForRegionRequest;
@@ -1412,7 +1413,7 @@ public class HBaseAdmin implements Admin {
    * @param nameOfRegionB encoded or full name of region b
    * @param forcible true if do a compulsory merge, otherwise we will only merge
    *          two adjacent regions
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    */
   @VisibleForTesting
   public void mergeRegionsSync(
@@ -1512,7 +1513,7 @@ public class HBaseAdmin implements Admin {
    *   Therefore, this is for internal testing only.
    * @param regionName encoded or full name of region
    * @param splitPoint key where region splits
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    */
   @VisibleForTesting
   public void splitRegionSync(byte[] regionName, byte[] splitPoint) throws IOException {
@@ -1526,7 +1527,7 @@ public class HBaseAdmin implements Admin {
    * @param splitPoint split point
    * @param timeout how long to wait on split
    * @param units time units
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    */
   public void splitRegionSync(byte[] regionName, byte[] splitPoint, final long timeout,
       final TimeUnit units) throws IOException {
@@ -1647,7 +1648,7 @@ public class HBaseAdmin implements Admin {
    *  MetaTableAccessor#getRegionLocation(Connection, byte[])}
    *  else null.
    * Throw IllegalArgumentException if <code>regionName</code> is null.
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    */
   Pair<RegionInfo, ServerName> getRegion(final byte[] regionName) throws IOException {
     if (regionName == null) {
@@ -1921,6 +1922,29 @@ public class HBaseAdmin implements Admin {
     });
   }
 
+  /**
+   * List available namespaces
+   * @return List of namespace names
+   * @throws IOException if a remote or network exception occurs
+   */
+  @Override
+  public String[] listNamespaces() throws IOException {
+    return executeCallable(new MasterCallable<String[]>(getConnection(),
+        getRpcControllerFactory()) {
+      @Override
+      protected String[] rpcCall() throws Exception {
+        List<String> list = master.listNamespaces(getRpcController(),
+          ListNamespacesRequest.newBuilder().build()).getNamespaceNameList();
+        return list.toArray(new String[list.size()]);
+      }
+    });
+  }
+
+  /**
+   * List available namespace descriptors
+   * @return List of descriptors
+   * @throws IOException if a remote or network exception occurs
+   */
   @Override
   public NamespaceDescriptor[] listNamespaceDescriptors() throws IOException {
     return executeCallable(new MasterCallable<NamespaceDescriptor[]>(getConnection(),
@@ -3594,7 +3618,7 @@ public class HBaseAdmin implements Admin {
    * </ol>
    * @param tableName name of the table to sync to the peer
    * @param splits table split keys
-   * @throws IOException
+   * @throws IOException if a remote or network exception occurs
    */
   private void checkAndSyncTableDescToPeers(final TableName tableName, final byte[][] splits)
       throws IOException {

hbase-client/src/main/java/org/apache/hadoop/hbase/client/RawAsyncHBaseAdmin.java

@@ -214,6 +214,8 @@ import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListDecomm
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListDecommissionedRegionServersResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespaceDescriptorsRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespaceDescriptorsResponse;
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespacesRequest;
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespacesResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableDescriptorsByNamespaceRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableDescriptorsByNamespaceResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableNamesByNamespaceRequest;
@@ -828,6 +830,18 @@ class RawAsyncHBaseAdmin implements AsyncAdmin {
                     .toNamespaceDescriptor(resp.getNamespaceDescriptor()))).call();
   }
 
+  @Override
+  public CompletableFuture<List<String>> listNamespaces() {
+    return this
+        .<List<String>> newMasterCaller()
+        .action(
+          (controller, stub) -> this
+              .<ListNamespacesRequest, ListNamespacesResponse, List<String>> call(
+                controller, stub, ListNamespacesRequest.newBuilder().build(), (s, c, req,
+                  done) -> s.listNamespaces(c, req, done),
+                (resp) -> resp.getNamespaceNameList())).call();
+  }
+
   @Override
   public CompletableFuture<List<NamespaceDescriptor>> listNamespaceDescriptors() {
     return this

hbase-client/src/main/java/org/apache/hadoop/hbase/client/ShortCircuitMasterConnection.java

@@ -31,6 +31,7 @@ import org.apache.hadoop.hbase.shaded.protobuf.generated.AccessControlProtos.Rev
 import org.apache.hadoop.hbase.shaded.protobuf.generated.AccessControlProtos.RevokeResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.ClientProtos.CoprocessorServiceRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.ClientProtos.CoprocessorServiceResponse;
+
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.AbortProcedureRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.AbortProcedureResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.AddColumnRequest;
@@ -107,6 +108,8 @@ import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListDecomm
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListDecommissionedRegionServersResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespaceDescriptorsRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespaceDescriptorsResponse;
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespacesRequest;
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespacesResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableDescriptorsByNamespaceRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableDescriptorsByNamespaceResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableNamesByNamespaceRequest;
@@ -446,6 +449,12 @@ public class ShortCircuitMasterConnection implements MasterKeepAliveConnection {
     return stub.getNamespaceDescriptor(controller, request);
   }
 
+  @Override
+  public ListNamespacesResponse listNamespaces(RpcController controller,
+      ListNamespacesRequest request) throws ServiceException {
+    return stub.listNamespaces(controller, request);
+  }
+
   @Override
   public MajorCompactionTimestampResponse getLastMajorCompactionTimestampForRegion(
       RpcController controller, MajorCompactionTimestampForRegionRequest request)

hbase-protocol-shaded/src/main/protobuf/Master.proto

@@ -237,6 +237,13 @@ message GetNamespaceDescriptorResponse {
   required NamespaceDescriptor namespaceDescriptor = 1;
 }
 
+message ListNamespacesRequest {
+}
+
+message ListNamespacesResponse {
+  repeated string namespaceName = 1;
+}
+
 message ListNamespaceDescriptorsRequest {
 }
 
@@ -916,7 +923,7 @@ service MasterService {
   rpc GetNamespaceDescriptor(GetNamespaceDescriptorRequest)
     returns(GetNamespaceDescriptorResponse);
 
-  /** returns a list of namespaces */
+  /** returns a list of namespace descriptors */
   rpc ListNamespaceDescriptors(ListNamespaceDescriptorsRequest)
     returns(ListNamespaceDescriptorsResponse);
 
@@ -1035,6 +1042,10 @@ service MasterService {
   rpc GetUserPermissions (GetUserPermissionsRequest) returns (GetUserPermissionsResponse);
 
   rpc HasUserPermissions (HasUserPermissionsRequest) returns (HasUserPermissionsResponse);
+
+  /** returns a list of namespace names */
+  rpc ListNamespaces(ListNamespacesRequest)
+    returns(ListNamespacesResponse);
 }
 
 // HBCK Service definitions.

hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MasterObserver.java

@@ -963,6 +963,24 @@ public interface MasterObserver {
   default void postGetNamespaceDescriptor(ObserverContext<MasterCoprocessorEnvironment> ctx,
       NamespaceDescriptor ns) throws IOException {}
 
+  /**
+   * Called before a listNamespaces request has been processed.
+   * @param ctx the environment to interact with the framework and master
+   * @param namespaces an empty list, can be filled with what to return if bypassing
+   * @throws IOException if something went wrong
+   */
+  default void preListNamespaces(ObserverContext<MasterCoprocessorEnvironment> ctx,
+      List<String> namespaces) throws IOException {}
+
+  /**
+   * Called after a listNamespaces request has been processed.
+   * @param ctx the environment to interact with the framework and master
+   * @param namespaces the list of namespaces about to be returned
+   * @throws IOException if something went wrong
+   */
+  default void postListNamespaces(ObserverContext<MasterCoprocessorEnvironment> ctx,
+      List<String> namespaces)  throws IOException {};
+
   /**
    * Called before a listNamespaceDescriptors request has been processed.
    * @param ctx the environment to interact with the framework and master

hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java

@@ -3392,6 +3392,25 @@ public class HMaster extends HRegionServer implements MasterServices {
     return nsds;
   }
 
+  /**
+   * List namespace names
+   * @return All namespace names
+   */
+  public List<String> listNamespaces() throws IOException {
+    checkInitialized();
+    List<String> namespaces = new ArrayList<>();
+    if (cpHost != null) {
+      cpHost.preListNamespaces(namespaces);
+    }
+    for (NamespaceDescriptor namespace : clusterSchemaService.getNamespaces()) {
+      namespaces.add(namespace.getName());
+    }
+    if (cpHost != null) {
+      cpHost.postListNamespaces(namespaces);
+    }
+    return namespaces;
+  }
+
   @Override
   public List<TableName> listTableNamesByNamespace(String name) throws IOException {
     checkInitialized();

hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterCoprocessorHost.java

@@ -297,6 +297,24 @@ public class MasterCoprocessorHost
     });
   }
 
+  public void preListNamespaces(final List<String> namespaces) throws IOException {
+    execOperation(coprocEnvironments.isEmpty() ? null : new MasterObserverOperation() {
+      @Override
+      public void call(MasterObserver oserver) throws IOException {
+        oserver.preListNamespaces(this, namespaces);
+      }
+    });
+  }
+
+  public void postListNamespaces(final List<String> namespaces) throws IOException {
+    execOperation(coprocEnvironments.isEmpty() ? null : new MasterObserverOperation() {
+      @Override
+      public void call(MasterObserver oserver) throws IOException {
+        oserver.postListNamespaces(this, namespaces);
+      }
+    });
+  }
+
   public void preListNamespaceDescriptors(final List<NamespaceDescriptor> descriptors)
       throws IOException {
     execOperation(coprocEnvironments.isEmpty() ? null : new MasterObserverOperation() {

hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterRpcServices.java

@@ -233,6 +233,8 @@ import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListDecomm
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListDecommissionedRegionServersResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespaceDescriptorsRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespaceDescriptorsResponse;
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespacesRequest;
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListNamespacesResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableDescriptorsByNamespaceRequest;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableDescriptorsByNamespaceResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos.ListTableNamesByNamespaceRequest;
@@ -994,6 +996,19 @@ public class MasterRpcServices extends RSRpcServices
     }
   }
 
+  @Override
+  public ListNamespacesResponse listNamespaces(
+      RpcController controller, ListNamespacesRequest request)
+      throws ServiceException {
+    try {
+      return ListNamespacesResponse.newBuilder()
+        .addAllNamespaceName(master.listNamespaces())
+        .build();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
+
   @Override
   public GetNamespaceDescriptorResponse getNamespaceDescriptor(
       RpcController controller, GetNamespaceDescriptorRequest request)

hbase-server/src/main/java/org/apache/hadoop/hbase/security/access/AccessController.java

@@ -1175,6 +1175,12 @@ public class AccessController implements MasterCoprocessor, RegionCoprocessor,
     requireNamespacePermission(ctx, "getNamespaceDescriptor", namespace, Action.ADMIN);
   }
 
+  @Override
+  public void postListNamespaces(ObserverContext<MasterCoprocessorEnvironment> ctx,
+      List<String> namespaces) throws IOException {
+    /* always allow namespace listing */
+  }
+
   @Override
   public void postListNamespaceDescriptors(ObserverContext<MasterCoprocessorEnvironment> ctx,
       List<NamespaceDescriptor> descriptors) throws IOException {

hbase-server/src/test/java/org/apache/hadoop/hbase/TestNamespace.java

@@ -110,6 +110,7 @@ public class TestNamespace {
     assertNotNull(ns);
     assertEquals(ns.getName(), NamespaceDescriptor.SYSTEM_NAMESPACE.getName());
 
+    assertEquals(2, admin.listNamespaces().length);
     assertEquals(2, admin.listNamespaceDescriptors().length);
 
     //verify existence of system tables
@@ -175,9 +176,11 @@ public class TestNamespace {
 
     //create namespace and verify
     admin.createNamespace(NamespaceDescriptor.create(nsName).build());
+    assertEquals(3, admin.listNamespaces().length);
     assertEquals(3, admin.listNamespaceDescriptors().length);
     //remove namespace and verify
     admin.deleteNamespace(nsName);
+    assertEquals(2, admin.listNamespaces().length);
     assertEquals(2, admin.listNamespaceDescriptors().length);
   }
 

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAsyncNamespaceAdminApi.java

@@ -71,9 +71,11 @@ public class TestAsyncNamespaceAdminApi extends TestAsyncAdminBase {
 
     // create namespace and verify
     admin.createNamespace(NamespaceDescriptor.create(nsName).build()).join();
+    assertEquals(3, admin.listNamespaces().get().size());
     assertEquals(3, admin.listNamespaceDescriptors().get().size());
     // delete namespace and verify
     admin.deleteNamespace(nsName).join();
+    assertEquals(2, admin.listNamespaces().get().size());
     assertEquals(2, admin.listNamespaceDescriptors().get().size());
   }
 

hbase-server/src/test/java/org/apache/hadoop/hbase/coprocessor/TestMasterObserver.java

@@ -111,6 +111,8 @@ public class TestMasterObserver {
     private boolean postModifyNamespaceCalled;
     private boolean preGetNamespaceDescriptorCalled;
     private boolean postGetNamespaceDescriptorCalled;
+    private boolean preListNamespacesCalled;
+    private boolean postListNamespacesCalled;
     private boolean preListNamespaceDescriptorsCalled;
     private boolean postListNamespaceDescriptorsCalled;
     private boolean preAddColumnCalled;
@@ -204,6 +206,8 @@ public class TestMasterObserver {
       postModifyNamespaceCalled = false;
       preGetNamespaceDescriptorCalled = false;
       postGetNamespaceDescriptorCalled = false;
+      preListNamespacesCalled = false;
+      postListNamespacesCalled = false;
       preListNamespaceDescriptorsCalled = false;
       postListNamespaceDescriptorsCalled = false;
       preAddColumnCalled = false;
@@ -472,6 +476,18 @@ public class TestMasterObserver {
       return preGetNamespaceDescriptorCalled && postGetNamespaceDescriptorCalled;
     }
 
+    @Override
+    public void preListNamespaces(ObserverContext<MasterCoprocessorEnvironment> ctx,
+        List<String> namespaces) {
+      preListNamespacesCalled = true;
+    }
+
+    @Override
+    public void postListNamespaces(ObserverContext<MasterCoprocessorEnvironment> ctx,
+        List<String> namespaces) {
+      postListNamespacesCalled = true;
+    }
+
     @Override
     public void preListNamespaceDescriptors(ObserverContext<MasterCoprocessorEnvironment> env,
         List<NamespaceDescriptor> descriptors) throws IOException {
@@ -1253,6 +1269,7 @@ public class TestMasterObserver {
         final ObserverContext<MasterCoprocessorEnvironment> ctx,
         final RegionInfo[] regionsToMerge) throws IOException {
     }
+
   }
 
   private static HBaseTestingUtility UTIL = new HBaseTestingUtility();
@@ -1495,6 +1512,11 @@ public class TestMasterObserver {
 
     // create a table
     Admin admin = UTIL.getAdmin();
+
+    admin.listNamespaces();
+    assertTrue("preListNamespaces should have been called", cp.preListNamespacesCalled);
+    assertTrue("postListNamespaces should have been called", cp.postListNamespacesCalled);
+
     admin.createNamespace(NamespaceDescriptor.create(testNamespace).build());
     assertTrue("Test namespace should be created", cp.wasCreateNamespaceCalled());
 

hbase-shell/src/main/ruby/hbase/admin.rb

@@ -1244,7 +1244,7 @@ module Hbase
     # Returns a list of namespaces in hbase
     def list_namespace(regex = '.*')
       pattern = java.util.regex.Pattern.compile(regex)
-      list = @admin.listNamespaceDescriptors.map(&:getName)
+      list = @admin.listNamespaces
       list.select { |s| pattern.match(s) }
     end
 

hbase-thrift/src/main/java/org/apache/hadoop/hbase/thrift2/ThriftHBaseServiceHandler.java

@@ -793,6 +793,20 @@ public class ThriftHBaseServiceHandler extends HBaseServiceHandler implements TH
     }
   }
 
+  @Override
+  public List<String> listNamespaces() throws TIOError, TException {
+    try {
+      String[] namespaces = connectionCache.getAdmin().listNamespaces();
+      List<String> result = new ArrayList<>(namespaces.length);
+      for (String ns: namespaces) {
+        result.add(ns);
+      }
+      return result;
+    } catch (IOException e) {
+      throw getTIOError(e);
+    }
+  }
+
   @Override
   public List<TNamespaceDescriptor> listNamespaceDescriptors() throws TIOError, TException {
     try {

hbase-thrift/src/main/java/org/apache/hadoop/hbase/thrift2/client/ThriftAdmin.java

@@ -395,6 +395,16 @@ public class ThriftAdmin implements Admin {
     }
   }
 
+  @Override
+  public String[] listNamespaces() throws IOException {
+    try {
+      List<String> tNamespaces = client.listNamespaces();
+      return tNamespaces.toArray(new String[tNamespaces.size()]);
+    } catch (TException e) {
+      throw new IOException(e);
+    }
+  }
+
   @Override
   public NamespaceDescriptor[] listNamespaceDescriptors() throws IOException {
     try {

hbase-thrift/src/main/java/org/apache/hadoop/hbase/thrift2/generated/THBaseService.java

@@ -494,6 +494,12 @@ public class THBaseService {
      */
     public java.util.List<TNamespaceDescriptor> listNamespaceDescriptors() throws TIOError, org.apache.thrift.TException;
 
+    /**
+     * @return all namespace names
+     * 
+     */
+    public java.util.List<java.lang.String> listNamespaces() throws TIOError, org.apache.thrift.TException;
+
   }
 
   public interface AsyncIface {
@@ -588,6 +594,8 @@ public class THBaseService {
 
     public void listNamespaceDescriptors(org.apache.thrift.async.AsyncMethodCallback<java.util.List<TNamespaceDescriptor>> resultHandler) throws org.apache.thrift.TException;
 
+    public void listNamespaces(org.apache.thrift.async.AsyncMethodCallback<java.util.List<java.lang.String>> resultHandler) throws org.apache.thrift.TException;
+
   }
 
   public static class Client extends org.apache.thrift.TServiceClient implements Iface {
@@ -1775,6 +1783,31 @@ public class THBaseService {
       throw new org.apache.thrift.TApplicationException(org.apache.thrift.TApplicationException.MISSING_RESULT, "listNamespaceDescriptors failed: unknown result");
     }
 
+    public java.util.List<java.lang.String> listNamespaces() throws TIOError, org.apache.thrift.TException
+    {
+      send_listNamespaces();
+      return recv_listNamespaces();
+    }
+
+    public void send_listNamespaces() throws org.apache.thrift.TException
+    {
+      listNamespaces_args args = new listNamespaces_args();
+      sendBase("listNamespaces", args);
+    }
+
+    public java.util.List<java.lang.String> recv_listNamespaces() throws TIOError, org.apache.thrift.TException
+    {
+      listNamespaces_result result = new listNamespaces_result();
+      receiveBase(result, "listNamespaces");
+      if (result.isSetSuccess()) {
+        return result.success;
+      }
+      if (result.io != null) {
+        throw result.io;
+      }
+      throw new org.apache.thrift.TApplicationException(org.apache.thrift.TApplicationException.MISSING_RESULT, "listNamespaces failed: unknown result");
+    }
+
   }
   public static class AsyncClient extends org.apache.thrift.async.TAsyncClient implements AsyncIface {
     public static class Factory implements org.apache.thrift.async.TAsyncClientFactory<AsyncClient> {
@@ -3353,6 +3386,35 @@ public class THBaseService {
       }
     }
 
+    public void listNamespaces(org.apache.thrift.async.AsyncMethodCallback<java.util.List<java.lang.String>> resultHandler) throws org.apache.thrift.TException {
+      checkReady();
+      listNamespaces_call method_call = new listNamespaces_call(resultHandler, this, ___protocolFactory, ___transport);
+      this.___currentMethod = method_call;
+      ___manager.call(method_call);
+    }
+
+    public static class listNamespaces_call extends org.apache.thrift.async.TAsyncMethodCall<java.util.List<java.lang.String>> {
+      public listNamespaces_call(org.apache.thrift.async.AsyncMethodCallback<java.util.List<java.lang.String>> resultHandler, org.apache.thrift.async.TAsyncClient client, org.apache.thrift.protocol.TProtocolFactory protocolFactory, org.apache.thrift.transport.TNonblockingTransport transport) throws org.apache.thrift.TException {
+        super(client, protocolFactory, transport, resultHandler, false);
+      }
+
+      public void write_args(org.apache.thrift.protocol.TProtocol prot) throws org.apache.thrift.TException {
+        prot.writeMessageBegin(new org.apache.thrift.protocol.TMessage("listNamespaces", org.apache.thrift.protocol.TMessageType.CALL, 0));
+        listNamespaces_args args = new listNamespaces_args();
+        args.write(prot);
+        prot.writeMessageEnd();
+      }
+
+      public java.util.List<java.lang.String> getResult() throws TIOError, org.apache.thrift.TException {
+        if (getState() != org.apache.thrift.async.TAsyncMethodCall.State.RESPONSE_READ) {
+          throw new java.lang.IllegalStateException("Method call not finished!");
+        }
+        org.apache.thrift.transport.TMemoryInputTransport memoryTransport = new org.apache.thrift.transport.TMemoryInputTransport(getFrameBuffer().array());
+        org.apache.thrift.protocol.TProtocol prot = client.getProtocolFactory().getProtocol(memoryTransport);
+        return (new Client(prot)).recv_listNamespaces();
+      }
+    }
+
   }
 
   public static class Processor<I extends Iface> extends org.apache.thrift.TBaseProcessor<I> implements org.apache.thrift.TProcessor {
@@ -3411,6 +3473,7 @@ public class THBaseService {
       processMap.put("deleteNamespace", new deleteNamespace());
       processMap.put("getNamespaceDescriptor", new getNamespaceDescriptor());
       processMap.put("listNamespaceDescriptors", new listNamespaceDescriptors());
+      processMap.put("listNamespaces", new listNamespaces());
       return processMap;
     }
 
@@ -4733,6 +4796,35 @@ public class THBaseService {
       }
     }
 
+    public static class listNamespaces<I extends Iface> extends org.apache.thrift.ProcessFunction<I, listNamespaces_args> {
+      public listNamespaces() {
+        super("listNamespaces");
+      }
+
+      public listNamespaces_args getEmptyArgsInstance() {
+        return new listNamespaces_args();
+      }
+
+      protected boolean isOneway() {
+        return false;
+      }
+
+      @Override
+      protected boolean rethrowUnhandledExceptions() {
+        return false;
+      }
+
+      public listNamespaces_result getResult(I iface, listNamespaces_args args) throws org.apache.thrift.TException {
+        listNamespaces_result result = new listNamespaces_result();
+        try {
+          result.success = iface.listNamespaces();
+        } catch (TIOError io) {
+          result.io = io;
+        }
+        return result;
+      }
+    }
+
   }
 
   public static class AsyncProcessor<I extends AsyncIface> extends org.apache.thrift.TBaseAsyncProcessor<I> {
@@ -4791,6 +4883,7 @@ public class THBaseService {
       processMap.put("deleteNamespace", new deleteNamespace());
       processMap.put("getNamespaceDescriptor", new getNamespaceDescriptor());
       processMap.put("listNamespaceDescriptors", new listNamespaceDescriptors());
+      processMap.put("listNamespaces", new listNamespaces());
       return processMap;
     }
 
@@ -7720,6 +7813,71 @@ public class THBaseService {
       }
     }
 
+    public static class listNamespaces<I extends AsyncIface> extends org.apache.thrift.AsyncProcessFunction<I, listNamespaces_args, java.util.List<java.lang.String>> {
+      public listNamespaces() {
+        super("listNamespaces");
+      }
+
+      public listNamespaces_args getEmptyArgsInstance() {
+        return new listNamespaces_args();
+      }
+
+      public org.apache.thrift.async.AsyncMethodCallback<java.util.List<java.lang.String>> getResultHandler(final org.apache.thrift.server.AbstractNonblockingServer.AsyncFrameBuffer fb, final int seqid) {
+        final org.apache.thrift.AsyncProcessFunction fcall = this;
+        return new org.apache.thrift.async.AsyncMethodCallback<java.util.List<java.lang.String>>() { 
+          public void onComplete(java.util.List<java.lang.String> o) {
+            listNamespaces_result result = new listNamespaces_result();
+            result.success = o;
+            try {
+              fcall.sendResponse(fb, result, org.apache.thrift.protocol.TMessageType.REPLY,seqid);
+            } catch (org.apache.thrift.transport.TTransportException e) {
+              _LOGGER.error("TTransportException writing to internal frame buffer", e);
+              fb.close();
+            } catch (java.lang.Exception e) {
+              _LOGGER.error("Exception writing to internal frame buffer", e);
+              onError(e);
+            }
+          }
+          public void onError(java.lang.Exception e) {
+            byte msgType = org.apache.thrift.protocol.TMessageType.REPLY;
+            org.apache.thrift.TSerializable msg;
+            listNamespaces_result result = new listNamespaces_result();
+            if (e instanceof TIOError) {
+              result.io = (TIOError) e;
+              result.setIoIsSet(true);
+              msg = result;
+            } else if (e instanceof org.apache.thrift.transport.TTransportException) {
+              _LOGGER.error("TTransportException inside handler", e);
+              fb.close();
+              return;
+            } else if (e instanceof org.apache.thrift.TApplicationException) {
+              _LOGGER.error("TApplicationException inside handler", e);
+              msgType = org.apache.thrift.protocol.TMessageType.EXCEPTION;
+              msg = (org.apache.thrift.TApplicationException)e;
+            } else {
+              _LOGGER.error("Exception inside handler", e);
+              msgType = org.apache.thrift.protocol.TMessageType.EXCEPTION;
+              msg = new org.apache.thrift.TApplicationException(org.apache.thrift.TApplicationException.INTERNAL_ERROR, e.getMessage());
+            }
+            try {
+              fcall.sendResponse(fb,msg,msgType,seqid);
+            } catch (java.lang.Exception ex) {
+              _LOGGER.error("Exception writing to internal frame buffer", ex);
+              fb.close();
+            }
+          }
+        };
+      }
+
+      protected boolean isOneway() {
+        return false;
+      }
+
+      public void start(I iface, listNamespaces_args args, org.apache.thrift.async.AsyncMethodCallback<java.util.List<java.lang.String>> resultHandler) throws org.apache.thrift.TException {
+        iface.listNamespaces(resultHandler);
+      }
+    }
+
   }
 
   public static class exists_args implements org.apache.thrift.TBase<exists_args, exists_args._Fields>, java.io.Serializable, Cloneable, Comparable<exists_args>   {
@@ -50391,4 +50549,782 @@ public class THBaseService {
     }
   }
 
+  public static class listNamespaces_args implements org.apache.thrift.TBase<listNamespaces_args, listNamespaces_args._Fields>, java.io.Serializable, Cloneable, Comparable<listNamespaces_args>   {
+    private static final org.apache.thrift.protocol.TStruct STRUCT_DESC = new org.apache.thrift.protocol.TStruct("listNamespaces_args");
+
+
+    private static final org.apache.thrift.scheme.SchemeFactory STANDARD_SCHEME_FACTORY = new listNamespaces_argsStandardSchemeFactory();
+    private static final org.apache.thrift.scheme.SchemeFactory TUPLE_SCHEME_FACTORY = new listNamespaces_argsTupleSchemeFactory();
+
+
+    /** The set of fields this struct contains, along with convenience methods for finding and manipulating them. */
+    public enum _Fields implements org.apache.thrift.TFieldIdEnum {
+;
+
+      private static final java.util.Map<java.lang.String, _Fields> byName = new java.util.HashMap<java.lang.String, _Fields>();
+
+      static {
+        for (_Fields field : java.util.EnumSet.allOf(_Fields.class)) {
+          byName.put(field.getFieldName(), field);
+        }
+      }
+
+      /**
+       * Find the _Fields constant that matches fieldId, or null if its not found.
+       */
+      @org.apache.thrift.annotation.Nullable
+      public static _Fields findByThriftId(int fieldId) {
+        switch(fieldId) {
+          default:
+            return null;
+        }
+      }
+
+      /**
+       * Find the _Fields constant that matches fieldId, throwing an exception
+       * if it is not found.
+       */
+      public static _Fields findByThriftIdOrThrow(int fieldId) {
+        _Fields fields = findByThriftId(fieldId);
+        if (fields == null) throw new java.lang.IllegalArgumentException("Field " + fieldId + " doesn't exist!");
+        return fields;
+      }
+
+      /**
+       * Find the _Fields constant that matches name, or null if its not found.
+       */
+      @org.apache.thrift.annotation.Nullable
+      public static _Fields findByName(java.lang.String name) {
+        return byName.get(name);
+      }
+
+      private final short _thriftId;
+      private final java.lang.String _fieldName;
+
+      _Fields(short thriftId, java.lang.String fieldName) {
+        _thriftId = thriftId;
+        _fieldName = fieldName;
+      }
+
+      public short getThriftFieldId() {
+        return _thriftId;
+      }
+
+      public java.lang.String getFieldName() {
+        return _fieldName;
+      }
+    }
+    public static final java.util.Map<_Fields, org.apache.thrift.meta_data.FieldMetaData> metaDataMap;
+    static {
+      java.util.Map<_Fields, org.apache.thrift.meta_data.FieldMetaData> tmpMap = new java.util.EnumMap<_Fields, org.apache.thrift.meta_data.FieldMetaData>(_Fields.class);
+      metaDataMap = java.util.Collections.unmodifiableMap(tmpMap);
+      org.apache.thrift.meta_data.FieldMetaData.addStructMetaDataMap(listNamespaces_args.class, metaDataMap);
+    }
+
+    public listNamespaces_args() {
+    }
+
+    /**
+     * Performs a deep copy on <i>other</i>.
+     */
+    public listNamespaces_args(listNamespaces_args other) {
+    }
+
+    public listNamespaces_args deepCopy() {
+      return new listNamespaces_args(this);
+    }
+
+    @Override
+    public void clear() {
+    }
+
+    public void setFieldValue(_Fields field, @org.apache.thrift.annotation.Nullable java.lang.Object value) {
+      switch (field) {
+      }
+    }
+
+    @org.apache.thrift.annotation.Nullable
+    public java.lang.Object getFieldValue(_Fields field) {
+      switch (field) {
+      }
+      throw new java.lang.IllegalStateException();
+    }
+
+    /** Returns true if field corresponding to fieldID is set (has been assigned a value) and false otherwise */
+    public boolean isSet(_Fields field) {
+      if (field == null) {
+        throw new java.lang.IllegalArgumentException();
+      }
+
+      switch (field) {
+      }
+      throw new java.lang.IllegalStateException();
+    }
+
+    @Override
+    public boolean equals(java.lang.Object that) {
+      if (that == null)
+        return false;
+      if (that instanceof listNamespaces_args)
+        return this.equals((listNamespaces_args)that);
+      return false;
+    }
+
+    public boolean equals(listNamespaces_args that) {
+      if (that == null)
+        return false;
+      if (this == that)
+        return true;
+
+      return true;
+    }
+
+    @Override
+    public int hashCode() {
+      int hashCode = 1;
+
+      return hashCode;
+    }
+
+    @Override
+    public int compareTo(listNamespaces_args other) {
+      if (!getClass().equals(other.getClass())) {
+        return getClass().getName().compareTo(other.getClass().getName());
+      }
+
+      int lastComparison = 0;
+
+      return 0;
+    }
+
+    @org.apache.thrift.annotation.Nullable
+    public _Fields fieldForId(int fieldId) {
+      return _Fields.findByThriftId(fieldId);
+    }
+
+    public void read(org.apache.thrift.protocol.TProtocol iprot) throws org.apache.thrift.TException {
+      scheme(iprot).read(iprot, this);
+    }
+
+    public void write(org.apache.thrift.protocol.TProtocol oprot) throws org.apache.thrift.TException {
+      scheme(oprot).write(oprot, this);
+    }
+
+    @Override
+    public java.lang.String toString() {
+      java.lang.StringBuilder sb = new java.lang.StringBuilder("listNamespaces_args(");
+      boolean first = true;
+
+      sb.append(")");
+      return sb.toString();
+    }
+
+    public void validate() throws org.apache.thrift.TException {
+      // check for required fields
+      // check for sub-struct validity
+    }
+
+    private void writeObject(java.io.ObjectOutputStream out) throws java.io.IOException {
+      try {
+        write(new org.apache.thrift.protocol.TCompactProtocol(new org.apache.thrift.transport.TIOStreamTransport(out)));
+      } catch (org.apache.thrift.TException te) {
+        throw new java.io.IOException(te);
+      }
+    }
+
+    private void readObject(java.io.ObjectInputStream in) throws java.io.IOException, java.lang.ClassNotFoundException {
+      try {
+        read(new org.apache.thrift.protocol.TCompactProtocol(new org.apache.thrift.transport.TIOStreamTransport(in)));
+      } catch (org.apache.thrift.TException te) {
+        throw new java.io.IOException(te);
+      }
+    }
+
+    private static class listNamespaces_argsStandardSchemeFactory implements org.apache.thrift.scheme.SchemeFactory {
+      public listNamespaces_argsStandardScheme getScheme() {
+        return new listNamespaces_argsStandardScheme();
+      }
+    }
+
+    private static class listNamespaces_argsStandardScheme extends org.apache.thrift.scheme.StandardScheme<listNamespaces_args> {
+
+      public void read(org.apache.thrift.protocol.TProtocol iprot, listNamespaces_args struct) throws org.apache.thrift.TException {
+        org.apache.thrift.protocol.TField schemeField;
+        iprot.readStructBegin();
+        while (true)
+        {
+          schemeField = iprot.readFieldBegin();
+          if (schemeField.type == org.apache.thrift.protocol.TType.STOP) { 
+            break;
+          }
+          switch (schemeField.id) {
+            default:
+              org.apache.thrift.protocol.TProtocolUtil.skip(iprot, schemeField.type);
+          }
+          iprot.readFieldEnd();
+        }
+        iprot.readStructEnd();
+
+        // check for required fields of primitive type, which can't be checked in the validate method
+        struct.validate();
+      }
+
+      public void write(org.apache.thrift.protocol.TProtocol oprot, listNamespaces_args struct) throws org.apache.thrift.TException {
+        struct.validate();
+
+        oprot.writeStructBegin(STRUCT_DESC);
+        oprot.writeFieldStop();
+        oprot.writeStructEnd();
+      }
+
+    }
+
+    private static class listNamespaces_argsTupleSchemeFactory implements org.apache.thrift.scheme.SchemeFactory {
+      public listNamespaces_argsTupleScheme getScheme() {
+        return new listNamespaces_argsTupleScheme();
+      }
+    }
+
+    private static class listNamespaces_argsTupleScheme extends org.apache.thrift.scheme.TupleScheme<listNamespaces_args> {
+
+      @Override
+      public void write(org.apache.thrift.protocol.TProtocol prot, listNamespaces_args struct) throws org.apache.thrift.TException {
+        org.apache.thrift.protocol.TTupleProtocol oprot = (org.apache.thrift.protocol.TTupleProtocol) prot;
+      }
+
+      @Override
+      public void read(org.apache.thrift.protocol.TProtocol prot, listNamespaces_args struct) throws org.apache.thrift.TException {
+        org.apache.thrift.protocol.TTupleProtocol iprot = (org.apache.thrift.protocol.TTupleProtocol) prot;
+      }
+    }
+
+    private static <S extends org.apache.thrift.scheme.IScheme> S scheme(org.apache.thrift.protocol.TProtocol proto) {
+      return (org.apache.thrift.scheme.StandardScheme.class.equals(proto.getScheme()) ? STANDARD_SCHEME_FACTORY : TUPLE_SCHEME_FACTORY).getScheme();
+    }
+  }
+
+  public static class listNamespaces_result implements org.apache.thrift.TBase<listNamespaces_result, listNamespaces_result._Fields>, java.io.Serializable, Cloneable, Comparable<listNamespaces_result>   {
+    private static final org.apache.thrift.protocol.TStruct STRUCT_DESC = new org.apache.thrift.protocol.TStruct("listNamespaces_result");
+
+    private static final org.apache.thrift.protocol.TField SUCCESS_FIELD_DESC = new org.apache.thrift.protocol.TField("success", org.apache.thrift.protocol.TType.LIST, (short)0);
+    private static final org.apache.thrift.protocol.TField IO_FIELD_DESC = new org.apache.thrift.protocol.TField("io", org.apache.thrift.protocol.TType.STRUCT, (short)1);
+
+    private static final org.apache.thrift.scheme.SchemeFactory STANDARD_SCHEME_FACTORY = new listNamespaces_resultStandardSchemeFactory();
+    private static final org.apache.thrift.scheme.SchemeFactory TUPLE_SCHEME_FACTORY = new listNamespaces_resultTupleSchemeFactory();
+
+    public @org.apache.thrift.annotation.Nullable java.util.List<java.lang.String> success; // required
+    public @org.apache.thrift.annotation.Nullable TIOError io; // required
+
+    /** The set of fields this struct contains, along with convenience methods for finding and manipulating them. */
+    public enum _Fields implements org.apache.thrift.TFieldIdEnum {
+      SUCCESS((short)0, "success"),
+      IO((short)1, "io");
+
+      private static final java.util.Map<java.lang.String, _Fields> byName = new java.util.HashMap<java.lang.String, _Fields>();
+
+      static {
+        for (_Fields field : java.util.EnumSet.allOf(_Fields.class)) {
+          byName.put(field.getFieldName(), field);
+        }
+      }
+
+      /**
+       * Find the _Fields constant that matches fieldId, or null if its not found.
+       */
+      @org.apache.thrift.annotation.Nullable
+      public static _Fields findByThriftId(int fieldId) {
+        switch(fieldId) {
+          case 0: // SUCCESS
+            return SUCCESS;
+          case 1: // IO
+            return IO;
+          default:
+            return null;
+        }
+      }
+
+      /**
+       * Find the _Fields constant that matches fieldId, throwing an exception
+       * if it is not found.
+       */
+      public static _Fields findByThriftIdOrThrow(int fieldId) {
+        _Fields fields = findByThriftId(fieldId);
+        if (fields == null) throw new java.lang.IllegalArgumentException("Field " + fieldId + " doesn't exist!");
+        return fields;
+      }
+
+      /**
+       * Find the _Fields constant that matches name, or null if its not found.
+       */
+      @org.apache.thrift.annotation.Nullable
+      public static _Fields findByName(java.lang.String name) {
+        return byName.get(name);
+      }
+
+      private final short _thriftId;
+      private final java.lang.String _fieldName;
+
+      _Fields(short thriftId, java.lang.String fieldName) {
+        _thriftId = thriftId;
+        _fieldName = fieldName;
+      }
+
+      public short getThriftFieldId() {
+        return _thriftId;
+      }
+
+      public java.lang.String getFieldName() {
+        return _fieldName;
+      }
+    }
+
+    // isset id assignments
+    public static final java.util.Map<_Fields, org.apache.thrift.meta_data.FieldMetaData> metaDataMap;
+    static {
+      java.util.Map<_Fields, org.apache.thrift.meta_data.FieldMetaData> tmpMap = new java.util.EnumMap<_Fields, org.apache.thrift.meta_data.FieldMetaData>(_Fields.class);
+      tmpMap.put(_Fields.SUCCESS, new org.apache.thrift.meta_data.FieldMetaData("success", org.apache.thrift.TFieldRequirementType.DEFAULT, 
+          new org.apache.thrift.meta_data.ListMetaData(org.apache.thrift.protocol.TType.LIST, 
+              new org.apache.thrift.meta_data.FieldValueMetaData(org.apache.thrift.protocol.TType.STRING))));
+      tmpMap.put(_Fields.IO, new org.apache.thrift.meta_data.FieldMetaData("io", org.apache.thrift.TFieldRequirementType.DEFAULT, 
+          new org.apache.thrift.meta_data.StructMetaData(org.apache.thrift.protocol.TType.STRUCT, TIOError.class)));
+      metaDataMap = java.util.Collections.unmodifiableMap(tmpMap);
+      org.apache.thrift.meta_data.FieldMetaData.addStructMetaDataMap(listNamespaces_result.class, metaDataMap);
+    }
+
+    public listNamespaces_result() {
+    }
+
+    public listNamespaces_result(
+      java.util.List<java.lang.String> success,
+      TIOError io)
+    {
+      this();
+      this.success = success;
+      this.io = io;
+    }
+
+    /**
+     * Performs a deep copy on <i>other</i>.
+     */
+    public listNamespaces_result(listNamespaces_result other) {
+      if (other.isSetSuccess()) {
+        java.util.List<java.lang.String> __this__success = new java.util.ArrayList<java.lang.String>(other.success);
+        this.success = __this__success;
+      }
+      if (other.isSetIo()) {
+        this.io = new TIOError(other.io);
+      }
+    }
+
+    public listNamespaces_result deepCopy() {
+      return new listNamespaces_result(this);
+    }
+
+    @Override
+    public void clear() {
+      this.success = null;
+      this.io = null;
+    }
+
+    public int getSuccessSize() {
+      return (this.success == null) ? 0 : this.success.size();
+    }
+
+    @org.apache.thrift.annotation.Nullable
+    public java.util.Iterator<java.lang.String> getSuccessIterator() {
+      return (this.success == null) ? null : this.success.iterator();
+    }
+
+    public void addToSuccess(java.lang.String elem) {
+      if (this.success == null) {
+        this.success = new java.util.ArrayList<java.lang.String>();
+      }
+      this.success.add(elem);
+    }
+
+    @org.apache.thrift.annotation.Nullable
+    public java.util.List<java.lang.String> getSuccess() {
+      return this.success;
+    }
+
+    public listNamespaces_result setSuccess(@org.apache.thrift.annotation.Nullable java.util.List<java.lang.String> success) {
+      this.success = success;
+      return this;
+    }
+
+    public void unsetSuccess() {
+      this.success = null;
+    }
+
+    /** Returns true if field success is set (has been assigned a value) and false otherwise */
+    public boolean isSetSuccess() {
+      return this.success != null;
+    }
+
+    public void setSuccessIsSet(boolean value) {
+      if (!value) {
+        this.success = null;
+      }
+    }
+
+    @org.apache.thrift.annotation.Nullable
+    public TIOError getIo() {
+      return this.io;
+    }
+
+    public listNamespaces_result setIo(@org.apache.thrift.annotation.Nullable TIOError io) {
+      this.io = io;
+      return this;
+    }
+
+    public void unsetIo() {
+      this.io = null;
+    }
+
+    /** Returns true if field io is set (has been assigned a value) and false otherwise */
+    public boolean isSetIo() {
+      return this.io != null;
+    }
+
+    public void setIoIsSet(boolean value) {
+      if (!value) {
+        this.io = null;
+      }
+    }
+
+    public void setFieldValue(_Fields field, @org.apache.thrift.annotation.Nullable java.lang.Object value) {
+      switch (field) {
+      case SUCCESS:
+        if (value == null) {
+          unsetSuccess();
+        } else {
+          setSuccess((java.util.List<java.lang.String>)value);
+        }
+        break;
+
+      case IO:
+        if (value == null) {
+          unsetIo();
+        } else {
+          setIo((TIOError)value);
+        }
+        break;
+
+      }
+    }
+
+    @org.apache.thrift.annotation.Nullable
+    public java.lang.Object getFieldValue(_Fields field) {
+      switch (field) {
+      case SUCCESS:
+        return getSuccess();
+
+      case IO:
+        return getIo();
+
+      }
+      throw new java.lang.IllegalStateException();
+    }
+
+    /** Returns true if field corresponding to fieldID is set (has been assigned a value) and false otherwise */
+    public boolean isSet(_Fields field) {
+      if (field == null) {
+        throw new java.lang.IllegalArgumentException();
+      }
+
+      switch (field) {
+      case SUCCESS:
+        return isSetSuccess();
+      case IO:
+        return isSetIo();
+      }
+      throw new java.lang.IllegalStateException();
+    }
+
+    @Override
+    public boolean equals(java.lang.Object that) {
+      if (that == null)
+        return false;
+      if (that instanceof listNamespaces_result)
+        return this.equals((listNamespaces_result)that);
+      return false;
+    }
+
+    public boolean equals(listNamespaces_result that) {
+      if (that == null)
+        return false;
+      if (this == that)
+        return true;
+
+      boolean this_present_success = true && this.isSetSuccess();
+      boolean that_present_success = true && that.isSetSuccess();
+      if (this_present_success || that_present_success) {
+        if (!(this_present_success && that_present_success))
+          return false;
+        if (!this.success.equals(that.success))
+          return false;
+      }
+
+      boolean this_present_io = true && this.isSetIo();
+      boolean that_present_io = true && that.isSetIo();
+      if (this_present_io || that_present_io) {
+        if (!(this_present_io && that_present_io))
+          return false;
+        if (!this.io.equals(that.io))
+          return false;
+      }
+
+      return true;
+    }
+
+    @Override
+    public int hashCode() {
+      int hashCode = 1;
+
+      hashCode = hashCode * 8191 + ((isSetSuccess()) ? 131071 : 524287);
+      if (isSetSuccess())
+        hashCode = hashCode * 8191 + success.hashCode();
+
+      hashCode = hashCode * 8191 + ((isSetIo()) ? 131071 : 524287);
+      if (isSetIo())
+        hashCode = hashCode * 8191 + io.hashCode();
+
+      return hashCode;
+    }
+
+    @Override
+    public int compareTo(listNamespaces_result other) {
+      if (!getClass().equals(other.getClass())) {
+        return getClass().getName().compareTo(other.getClass().getName());
+      }
+
+      int lastComparison = 0;
+
+      lastComparison = java.lang.Boolean.valueOf(isSetSuccess()).compareTo(other.isSetSuccess());
+      if (lastComparison != 0) {
+        return lastComparison;
+      }
+      if (isSetSuccess()) {
+        lastComparison = org.apache.thrift.TBaseHelper.compareTo(this.success, other.success);
+        if (lastComparison != 0) {
+          return lastComparison;
+        }
+      }
+      lastComparison = java.lang.Boolean.valueOf(isSetIo()).compareTo(other.isSetIo());
+      if (lastComparison != 0) {
+        return lastComparison;
+      }
+      if (isSetIo()) {
+        lastComparison = org.apache.thrift.TBaseHelper.compareTo(this.io, other.io);
+        if (lastComparison != 0) {
+          return lastComparison;
+        }
+      }
+      return 0;
+    }
+
+    @org.apache.thrift.annotation.Nullable
+    public _Fields fieldForId(int fieldId) {
+      return _Fields.findByThriftId(fieldId);
+    }
+
+    public void read(org.apache.thrift.protocol.TProtocol iprot) throws org.apache.thrift.TException {
+      scheme(iprot).read(iprot, this);
+    }
+
+    public void write(org.apache.thrift.protocol.TProtocol oprot) throws org.apache.thrift.TException {
+      scheme(oprot).write(oprot, this);
+      }
+
+    @Override
+    public java.lang.String toString() {
+      java.lang.StringBuilder sb = new java.lang.StringBuilder("listNamespaces_result(");
+      boolean first = true;
+
+      sb.append("success:");
+      if (this.success == null) {
+        sb.append("null");
+      } else {
+        sb.append(this.success);
+      }
+      first = false;
+      if (!first) sb.append(", ");
+      sb.append("io:");
+      if (this.io == null) {
+        sb.append("null");
+      } else {
+        sb.append(this.io);
+      }
+      first = false;
+      sb.append(")");
+      return sb.toString();
+    }
+
+    public void validate() throws org.apache.thrift.TException {
+      // check for required fields
+      // check for sub-struct validity
+    }
+
+    private void writeObject(java.io.ObjectOutputStream out) throws java.io.IOException {
+      try {
+        write(new org.apache.thrift.protocol.TCompactProtocol(new org.apache.thrift.transport.TIOStreamTransport(out)));
+      } catch (org.apache.thrift.TException te) {
+        throw new java.io.IOException(te);
+      }
+    }
+
+    private void readObject(java.io.ObjectInputStream in) throws java.io.IOException, java.lang.ClassNotFoundException {
+      try {
+        read(new org.apache.thrift.protocol.TCompactProtocol(new org.apache.thrift.transport.TIOStreamTransport(in)));
+      } catch (org.apache.thrift.TException te) {
+        throw new java.io.IOException(te);
+      }
+    }
+
+    private static class listNamespaces_resultStandardSchemeFactory implements org.apache.thrift.scheme.SchemeFactory {
+      public listNamespaces_resultStandardScheme getScheme() {
+        return new listNamespaces_resultStandardScheme();
+      }
+    }
+
+    private static class listNamespaces_resultStandardScheme extends org.apache.thrift.scheme.StandardScheme<listNamespaces_result> {
+
+      public void read(org.apache.thrift.protocol.TProtocol iprot, listNamespaces_result struct) throws org.apache.thrift.TException {
+        org.apache.thrift.protocol.TField schemeField;
+        iprot.readStructBegin();
+        while (true)
+        {
+          schemeField = iprot.readFieldBegin();
+          if (schemeField.type == org.apache.thrift.protocol.TType.STOP) { 
+            break;
+          }
+          switch (schemeField.id) {
+            case 0: // SUCCESS
+              if (schemeField.type == org.apache.thrift.protocol.TType.LIST) {
+                {
+                  org.apache.thrift.protocol.TList _list342 = iprot.readListBegin();
+                  struct.success = new java.util.ArrayList<java.lang.String>(_list342.size);
+                  @org.apache.thrift.annotation.Nullable java.lang.String _elem343;
+                  for (int _i344 = 0; _i344 < _list342.size; ++_i344)
+                  {
+                    _elem343 = iprot.readString();
+                    struct.success.add(_elem343);
+                  }
+                  iprot.readListEnd();
+                }
+                struct.setSuccessIsSet(true);
+              } else { 
+                org.apache.thrift.protocol.TProtocolUtil.skip(iprot, schemeField.type);
+              }
+              break;
+            case 1: // IO
+              if (schemeField.type == org.apache.thrift.protocol.TType.STRUCT) {
+                struct.io = new TIOError();
+                struct.io.read(iprot);
+                struct.setIoIsSet(true);
+              } else { 
+                org.apache.thrift.protocol.TProtocolUtil.skip(iprot, schemeField.type);
+              }
+              break;
+            default:
+              org.apache.thrift.protocol.TProtocolUtil.skip(iprot, schemeField.type);
+          }
+          iprot.readFieldEnd();
+        }
+        iprot.readStructEnd();
+
+        // check for required fields of primitive type, which can't be checked in the validate method
+        struct.validate();
+      }
+
+      public void write(org.apache.thrift.protocol.TProtocol oprot, listNamespaces_result struct) throws org.apache.thrift.TException {
+        struct.validate();
+
+        oprot.writeStructBegin(STRUCT_DESC);
+        if (struct.success != null) {
+          oprot.writeFieldBegin(SUCCESS_FIELD_DESC);
+          {
+            oprot.writeListBegin(new org.apache.thrift.protocol.TList(org.apache.thrift.protocol.TType.STRING, struct.success.size()));
+            for (java.lang.String _iter345 : struct.success)
+            {
+              oprot.writeString(_iter345);
+            }
+            oprot.writeListEnd();
+          }
+          oprot.writeFieldEnd();
+        }
+        if (struct.io != null) {
+          oprot.writeFieldBegin(IO_FIELD_DESC);
+          struct.io.write(oprot);
+          oprot.writeFieldEnd();
+        }
+        oprot.writeFieldStop();
+        oprot.writeStructEnd();
+      }
+
+    }
+
+    private static class listNamespaces_resultTupleSchemeFactory implements org.apache.thrift.scheme.SchemeFactory {
+      public listNamespaces_resultTupleScheme getScheme() {
+        return new listNamespaces_resultTupleScheme();
+      }
+    }
+
+    private static class listNamespaces_resultTupleScheme extends org.apache.thrift.scheme.TupleScheme<listNamespaces_result> {
+
+      @Override
+      public void write(org.apache.thrift.protocol.TProtocol prot, listNamespaces_result struct) throws org.apache.thrift.TException {
+        org.apache.thrift.protocol.TTupleProtocol oprot = (org.apache.thrift.protocol.TTupleProtocol) prot;
+        java.util.BitSet optionals = new java.util.BitSet();
+        if (struct.isSetSuccess()) {
+          optionals.set(0);
+        }
+        if (struct.isSetIo()) {
+          optionals.set(1);
+        }
+        oprot.writeBitSet(optionals, 2);
+        if (struct.isSetSuccess()) {
+          {
+            oprot.writeI32(struct.success.size());
+            for (java.lang.String _iter346 : struct.success)
+            {
+              oprot.writeString(_iter346);
+            }
+          }
+        }
+        if (struct.isSetIo()) {
+          struct.io.write(oprot);
+        }
+      }
+
+      @Override
+      public void read(org.apache.thrift.protocol.TProtocol prot, listNamespaces_result struct) throws org.apache.thrift.TException {
+        org.apache.thrift.protocol.TTupleProtocol iprot = (org.apache.thrift.protocol.TTupleProtocol) prot;
+        java.util.BitSet incoming = iprot.readBitSet(2);
+        if (incoming.get(0)) {
+          {
+            org.apache.thrift.protocol.TList _list347 = new org.apache.thrift.protocol.TList(org.apache.thrift.protocol.TType.STRING, iprot.readI32());
+            struct.success = new java.util.ArrayList<java.lang.String>(_list347.size);
+            @org.apache.thrift.annotation.Nullable java.lang.String _elem348;
+            for (int _i349 = 0; _i349 < _list347.size; ++_i349)
+            {
+              _elem348 = iprot.readString();
+              struct.success.add(_elem348);
+            }
+          }
+          struct.setSuccessIsSet(true);
+        }
+        if (incoming.get(1)) {
+          struct.io = new TIOError();
+          struct.io.read(iprot);
+          struct.setIoIsSet(true);
+        }
+      }
+    }
+
+    private static <S extends org.apache.thrift.scheme.IScheme> S scheme(org.apache.thrift.protocol.TProtocol proto) {
+      return (org.apache.thrift.scheme.StandardScheme.class.equals(proto.getScheme()) ? STANDARD_SCHEME_FACTORY : TUPLE_SCHEME_FACTORY).getScheme();
+    }
+  }
+
 }

hbase-thrift/src/main/resources/org/apache/hadoop/hbase/thrift2/hbase.thrift

@@ -1032,4 +1032,10 @@ service THBaseService {
   **/
   list<TNamespaceDescriptor> listNamespaceDescriptors(
   ) throws (1: TIOError io)
+
+  /**
+  * @return all namespace names
+  **/
+  list<string> listNamespaces(
+  ) throws (1: TIOError io)
 }