HDFS-15535. RBF: Fix Namespace path to snapshot path resolution for snapshot API. Contributed by Ayush Saxena.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterRpcClient.java

@@ -849,6 +849,45 @@ public class RouterRpcClient {
       final List<? extends RemoteLocationContext> locations,
       final RemoteMethod remoteMethod, Class<T> expectedResultClass,
       Object expectedResultValue) throws IOException {
+    return (T) invokeSequential(remoteMethod, locations, expectedResultClass,
+        expectedResultValue).getResult();
+  }
+
+  /**
+   * Invokes sequential proxy calls to different locations. Continues to invoke
+   * calls until the success condition is met, or until all locations have been
+   * attempted.
+   *
+   * The success condition may be specified by:
+   * <ul>
+   * <li>An expected result class
+   * <li>An expected result value
+   * </ul>
+   *
+   * If no expected result class/values are specified, the success condition is
+   * a call that does not throw a remote exception.
+   *
+   * This returns RemoteResult, which contains the invoked location as well
+   * as the result.
+   *
+   * @param <R> The type of the remote location.
+   * @param <T> The type of the remote method return.
+   * @param remoteMethod The remote method and parameters to invoke.
+   * @param locations List of locations/nameservices to call concurrently.
+   * @param expectedResultClass In order to be considered a positive result, the
+   *          return type must be of this class.
+   * @param expectedResultValue In order to be considered a positive result, the
+   *          return value must equal the value of this object.
+   * @return The result of the first successful call, or if no calls are
+   *         successful, the result of the first RPC call executed, along with
+   *         the invoked location in form of RemoteResult.
+   * @throws IOException if the success condition is not met, return the first
+   *                     remote exception generated.
+   */
+  public <R extends RemoteLocationContext, T> RemoteResult invokeSequential(
+      final RemoteMethod remoteMethod, final List<R> locations,
+      Class<T> expectedResultClass, Object expectedResultValue)
+      throws IOException {
 
     final UserGroupInformation ugi = RouterRpcServer.getRemoteUser();
     final Method m = remoteMethod.getMethod();
@@ -867,9 +906,9 @@ public class RouterRpcClient {
         if (isExpectedClass(expectedResultClass, result) &&
             isExpectedValue(expectedResultValue, result)) {
           // Valid result, stop here
-          @SuppressWarnings("unchecked")
-          T ret = (T)result;
-          return ret;
+          @SuppressWarnings("unchecked") R location = (R) loc;
+          @SuppressWarnings("unchecked") T ret = (T) result;
+          return new RemoteResult<>(location, ret);
         }
         if (firstResult == null) {
           firstResult = result;
@@ -907,9 +946,8 @@ public class RouterRpcClient {
       throw thrownExceptions.get(0);
     }
     // Return the first result, whether it is the value or not
-    @SuppressWarnings("unchecked")
-    T ret = (T)firstResult;
-    return ret;
+    @SuppressWarnings("unchecked") T ret = (T) firstResult;
+    return new RemoteResult<>(locations.get(0), ret);
   }
 
   /**

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterSnapshot.java

@@ -104,10 +104,12 @@ public class RouterSnapshot {
       result = firstelement.getValue();
       result = result.replaceFirst(loc.getDest(), loc.getSrc());
     } else {
-      result = rpcClient.invokeSequential(
-          locations, method, String.class, null);
-      RemoteLocation loc = locations.get(0);
-      result = result.replaceFirst(loc.getDest(), loc.getSrc());
+      RemoteResult<RemoteLocation, String> response =
+          rpcClient.invokeSequential(method, locations, String.class, null);
+      RemoteLocation loc = response.getLocation();
+      String invokedResult = response.getResult();
+      result = invokedResult
+          .replaceFirst(loc.getDest(), loc.getSrc());
     }
     return result;
   }
@@ -180,9 +182,11 @@ public class RouterSnapshot {
         s.setParentFullPath(DFSUtil.string2Bytes(mountPath));
       }
     } else {
-      response = rpcClient.invokeSequential(
-          locations, remoteMethod, SnapshotStatus[].class, null);
-      RemoteLocation loc = locations.get(0);
+      RemoteResult<RemoteLocation, SnapshotStatus[]> invokedResponse = rpcClient
+          .invokeSequential(remoteMethod, locations, SnapshotStatus[].class,
+              null);
+      RemoteLocation loc = invokedResponse.getLocation();
+      response = invokedResponse.getResult();
       for (SnapshotStatus s : response) {
         String mountPath = DFSUtil.bytes2String(s.getParentFullPath()).
             replaceFirst(loc.getDest(), loc.getSrc());

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/router/TestRouterRPCMultipleDestinationMountTableResolver.java

@@ -43,6 +43,7 @@ import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.DFSTestUtil;
 import org.apache.hadoop.hdfs.DistributedFileSystem;
+import org.apache.hadoop.hdfs.protocol.SnapshotStatus;
 import org.apache.hadoop.hdfs.server.federation.MiniRouterDFSCluster.RouterContext;
 import org.apache.hadoop.hdfs.server.federation.RouterConfigBuilder;
 import org.apache.hadoop.hdfs.server.federation.StateStoreDFSCluster;
@@ -492,6 +493,38 @@ public class TestRouterRPCMultipleDestinationMountTableResolver {
     assertFalse(client.isMultiDestDirectory("/mount/dir"));
   }
 
+  /**
+   * Verifies the snapshot location returned after snapshot operations is in
+   * accordance to the mount path.
+   */
+  @Test
+  public void testSnapshotPathResolution() throws Exception {
+    // Create a mount entry with non isPathAll order, so as to call
+    // invokeSequential.
+    Map<String, String> destMap = new HashMap<>();
+    destMap.put("ns0", "/tmp_ns0");
+    destMap.put("ns1", "/tmp_ns1");
+    nnFs0.mkdirs(new Path("/tmp_ns0"));
+    nnFs1.mkdirs(new Path("/tmp_ns1"));
+    MountTable addEntry = MountTable.newInstance("/mountSnap", destMap);
+    addEntry.setDestOrder(DestinationOrder.HASH);
+    assertTrue(addMountTable(addEntry));
+    // Create the actual directory in the destination second in sequence of
+    // invokeSequential.
+    nnFs0.mkdirs(new Path("/tmp_ns0/snapDir"));
+    Path snapDir = new Path("/mountSnap/snapDir");
+    Path snapshotPath = new Path("/mountSnap/snapDir/.snapshot/snap");
+    routerFs.allowSnapshot(snapDir);
+    // Verify the snapshot path returned after createSnapshot is as per mount
+    // path.
+    Path snapshot = routerFs.createSnapshot(snapDir, "snap");
+    assertEquals(snapshotPath, snapshot);
+    // Verify the snapshot path returned as part of snapshotListing is as per
+    // mount path.
+    SnapshotStatus[] snapshots = routerFs.getSnapshotListing(snapDir);
+    assertEquals(snapshotPath, snapshots[0].getFullPath());
+  }
+
   @Test
   public void testRenameMultipleDestDirectories() throws Exception {
     // Test renaming directories using rename API.