HADOOP-19464. S3A: Restore Compatibility with EMRFS FileSystem (#7410)

After HADOOP-19278, The S3N folder marker _$folder$ is not skipped during
listing of S3 directories. This can lead to the S3A filesystem failing to read
data written by the legacy Hadoop S3N filesystem and AWS EMR's EMRFS
("S3" filesystem)

Contributed by Syed Shameerur Rahman

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/Listing.java

@@ -50,6 +50,7 @@ import java.util.NoSuchElementException;
 import java.util.concurrent.CompletableFuture;
 import java.util.StringJoiner;
 
+import static org.apache.hadoop.fs.s3a.Constants.S3N_FOLDER_SUFFIX;
 import static org.apache.hadoop.fs.s3a.Invoker.onceInTheFuture;
 import static org.apache.hadoop.fs.s3a.S3AUtils.createFileStatus;
 import static org.apache.hadoop.fs.s3a.S3AUtils.maybeAddTrailingSlash;
@@ -74,6 +75,9 @@ public class Listing extends AbstractStoreOperation {
 
   private static final Logger LOG = S3AFileSystem.LOG;
 
+  static final FileStatusAcceptor ACCEPT_ALL_BUT_S3N =
+      new AcceptAllButS3nDirs();
+
   static final FileStatusAcceptor ACCEPT_ALL_OBJECTS =
       new AcceptAllObjects();
 
@@ -114,7 +118,7 @@ public class Listing extends AbstractStoreOperation {
           S3AFileStatus[] fileStatuses) {
     return filteringRemoteIterator(
         remoteIteratorFromArray(fileStatuses),
-        Listing.ACCEPT_ALL_OBJECTS::accept);
+        Listing.ACCEPT_ALL_BUT_S3N::accept);
   }
 
   /**
@@ -233,7 +237,7 @@ public class Listing extends AbstractStoreOperation {
             listingOperationCallbacks
                 .createListObjectsRequest(key, "/", span),
             filter,
-            new AcceptAllButSelf(dir),
+            new AcceptAllButSelfAndS3nDirs(dir),
             span));
   }
 
@@ -262,7 +266,7 @@ public class Listing extends AbstractStoreOperation {
         path,
         request,
         S3AUtils.ACCEPT_ALL,
-        new AcceptAllButSelf(path),
+        new AcceptAllButSelfAndS3nDirs(path),
         span);
   }
 
@@ -460,7 +464,7 @@ public class Listing extends AbstractStoreOperation {
         if (LOG.isDebugEnabled()) {
           LOG.debug("{}: {}", keyPath, stringify(s3Object));
         }
-        // Skip over keys that are ourselves
+        // Skip over keys that are ourselves and old S3N _$folder$ files
         if (acceptor.accept(keyPath, s3Object) && filter.accept(keyPath)) {
           S3AFileStatus status = createFileStatus(keyPath, s3Object,
               blockSize, userName, s3Object.eTag(),
@@ -720,7 +724,8 @@ public class Listing extends AbstractStoreOperation {
   }
 
   /**
-   * Accept all entries except the base path.
+   * Accept all entries except the base path and those which map to S3N
+   * pseudo directory markers.
    */
   static class AcceptFilesOnly implements FileStatusAcceptor {
     private final Path qualifiedPath;
@@ -740,6 +745,7 @@ public class Listing extends AbstractStoreOperation {
     @Override
     public boolean accept(Path keyPath, S3Object s3Object) {
       return !keyPath.equals(qualifiedPath)
+          && !s3Object.key().endsWith(S3N_FOLDER_SUFFIX)
           && !objectRepresentsDirectory(s3Object.key());
     }
 
@@ -760,6 +766,25 @@ public class Listing extends AbstractStoreOperation {
     }
   }
 
+  /**
+   * Accept all entries except those which map to S3N pseudo directory markers.
+   */
+  static class AcceptAllButS3nDirs implements FileStatusAcceptor {
+
+    public boolean accept(Path keyPath, S3Object s3Object) {
+      return !s3Object.key().endsWith(S3N_FOLDER_SUFFIX);
+    }
+
+    public boolean accept(Path keyPath, String prefix) {
+      return !keyPath.toString().endsWith(S3N_FOLDER_SUFFIX);
+    }
+
+    public boolean accept(FileStatus status) {
+      return !status.getPath().toString().endsWith(S3N_FOLDER_SUFFIX);
+    }
+
+  }
+
   /**
    * Accept all entries.
    */
@@ -779,6 +804,55 @@ public class Listing extends AbstractStoreOperation {
 
   }
 
+  /**
+   * Accept all entries except the base path and those which map to S3N
+   * pseudo directory markers.
+   */
+  public static class AcceptAllButSelfAndS3nDirs implements FileStatusAcceptor {
+
+    /** Base path. */
+    private final Path qualifiedPath;
+
+    /**
+     * Constructor.
+     * @param qualifiedPath an already-qualified path.
+     */
+    public AcceptAllButSelfAndS3nDirs(Path qualifiedPath) {
+      this.qualifiedPath = qualifiedPath;
+    }
+
+    /**
+     * Reject a s3Object entry if the key path is the qualified Path, or
+     * it ends with {@code "_$folder$"}.
+     * @param keyPath key path of the entry
+     * @param s3Object s3Object entry
+     * @return true if the entry is accepted (i.e. that a status entry
+     * should be generated.)
+     */
+    @Override
+    public boolean accept(Path keyPath, S3Object s3Object) {
+      return !keyPath.equals(qualifiedPath) &&
+          !s3Object.key().endsWith(S3N_FOLDER_SUFFIX);
+    }
+
+    /**
+     * Accept all prefixes except the one for the base path, "self".
+     * @param keyPath qualified path to the entry
+     * @param prefix common prefix in listing.
+     * @return true if the entry is accepted (i.e. that a status entry
+     * should be generated.
+     */
+    @Override
+    public boolean accept(Path keyPath, String prefix) {
+      return !keyPath.equals(qualifiedPath);
+    }
+
+    @Override
+    public boolean accept(FileStatus status) {
+      return (status != null) && !status.getPath().equals(qualifiedPath);
+    }
+  }
+
   /**
    * Accept all entries except the base path.
    */

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java

@@ -2585,7 +2585,7 @@ public class S3AFileSystem extends FileSystem implements StreamCapabilities,
           listing.createFileStatusListingIterator(path,
               createListObjectsRequest(key, null),
               ACCEPT_ALL,
-              Listing.ACCEPT_ALL_OBJECTS,
+              Listing.ACCEPT_ALL_BUT_S3N,
               auditSpan));
     }
 
@@ -3613,7 +3613,7 @@ public class S3AFileSystem extends FileSystem implements StreamCapabilities,
         return listing.createProvidedFileStatusIterator(
                 stats,
                 ACCEPT_ALL,
-                Listing.ACCEPT_ALL_OBJECTS);
+                Listing.ACCEPT_ALL_BUT_S3N);
       }
     }
     // Here we have a directory which may or may not be empty.
@@ -3797,7 +3797,7 @@ public class S3AFileSystem extends FileSystem implements StreamCapabilities,
     @Override
     public RemoteIterator<S3ALocatedFileStatus> listFilesIterator(final Path path,
         final boolean recursive) throws IOException {
-      return S3AFileSystem.this.innerListFiles(path, recursive, Listing.ACCEPT_ALL_OBJECTS, null);
+      return S3AFileSystem.this.innerListFiles(path, recursive, Listing.ACCEPT_ALL_BUT_S3N, null);
     }
   }
 
@@ -5026,7 +5026,7 @@ public class S3AFileSystem extends FileSystem implements StreamCapabilities,
     final Path path = qualify(f);
     return trackDurationAndSpan(INVOCATION_LIST_FILES, path, () ->
         innerListFiles(path, recursive,
-            Listing.ACCEPT_ALL_OBJECTS,
+            Listing.ACCEPT_ALL_BUT_S3N,
             null));
   }
 

hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/s3a/ITestEMRFSCompatibility.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.fs.s3a;
+
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+
+import org.apache.hadoop.fs.Path;
+
+import static org.apache.hadoop.fs.contract.ContractTestUtils.touch;
+import static org.apache.hadoop.fs.s3a.Constants.S3N_FOLDER_SUFFIX;
+
+/**
+ * This test verifies that the EMRFS or legacy S3N filesystem compatibility with
+ * S3A works as expected.
+ */
+public class ITestEMRFSCompatibility extends AbstractS3ATestBase {
+  private static final String SRC_DIR = "src";
+  private static final String DEST_DIR = "dest";
+  private static final String SUBDIR = "subdir";
+
+  @Test
+  public void testFileSystemOperationWithS3NFolderMarker() throws Throwable {
+    S3AFileSystem fs = getFileSystem();
+    Path basePath = methodPath();
+    Path src = new Path(basePath, SRC_DIR);
+    Path dest = new Path(basePath, DEST_DIR);
+    Path subdir = new Path(src, SUBDIR);
+    Path folderMarker = new Path(subdir, S3N_FOLDER_SUFFIX);
+
+    // write an empty S3N folder marker object
+    touch(fs, folderMarker);
+
+    // verify initial state
+    Assertions.assertThat(fs.listStatus(subdir))
+        .describedAs("No objects are expected to be listed")
+        .isEmpty();
+
+    // rename the src folder.
+    fs.rename(src, dest);
+
+    //verify destination folder exists
+    Assertions.assertThat(fs.exists(new Path(dest, "subdir")))
+        .describedAs("Destination folder should exist")
+        .isTrue();
+
+    // verify src folder does not exists
+    Assertions.assertThat(fs.exists(src))
+        .describedAs("Source folder should not exist after rename")
+        .isFalse();
+  }
+}