HBASE-27950 ClientSideRegionScanner does not adhere to RegionScanner.nextRaw contract

hbase-server/src/main/java/org/apache/hadoop/hbase/client/ClientSideRegionScanner.java

@@ -48,6 +48,7 @@ public class ClientSideRegionScanner extends AbstractClientScanner {
   private HRegion region;
   RegionScanner scanner;
   List<Cell> values;
+  boolean hasMore = true;
 
   public ClientSideRegionScanner(Configuration conf, FileSystem fs, Path rootDir,
     TableDescriptor htd, RegionInfo hri, Scan scan, ScanMetrics scanMetrics) throws IOException {
@@ -90,12 +91,13 @@ public ClientSideRegionScanner(Configuration conf, FileSystem fs, Path rootDir,
 
   @Override
   public Result next() throws IOException {
-    values.clear();
-    scanner.nextRaw(values);
-    if (values.isEmpty()) {
-      // we are done
-      return null;
-    }
+    do {
+      if (!hasMore) {
+        return null;
+      }
+      values.clear();
+      this.hasMore = scanner.nextRaw(values);
+    } while (values.isEmpty());
 
     Result result = Result.create(values);
     if (this.scanMetrics != null) {

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

@@ -17,22 +17,34 @@
  */
 package org.apache.hadoop.hbase.client;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.anyList;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 
 import java.io.IOException;
+import java.util.Arrays;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hbase.Cell;
 import org.apache.hadoop.hbase.HBaseClassTestRule;
 import org.apache.hadoop.hbase.HBaseTestingUtil;
 import org.apache.hadoop.hbase.HConstants;
 import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.filter.FilterBase;
 import org.apache.hadoop.hbase.io.hfile.BlockCache;
 import org.apache.hadoop.hbase.io.hfile.IndexOnlyLruBlockCache;
+import org.apache.hadoop.hbase.regionserver.RegionScanner;
+import org.apache.hadoop.hbase.regionserver.StoreScanner;
 import org.apache.hadoop.hbase.testclassification.ClientTests;
 import org.apache.hadoop.hbase.testclassification.SmallTests;
+import org.apache.hadoop.hbase.util.Bytes;
 import org.junit.AfterClass;
 import org.junit.Before;
 import org.junit.BeforeClass;
@@ -47,6 +59,8 @@ public class TestClientSideRegionScanner {
     HBaseClassTestRule.forClass(TestClientSideRegionScanner.class);
 
   private final static HBaseTestingUtil TEST_UTIL = new HBaseTestingUtil();
+  private static final TableName TABLE_NAME = TableName.valueOf("test");
+  private static final byte[] FAM_NAME = Bytes.toBytes("f");
 
   private Configuration conf;
   private Path rootDir;
@@ -113,4 +127,78 @@ public void testNoBlockCache() throws IOException {
     BlockCache blockCache = clientSideRegionScanner.getRegion().getBlockCache();
     assertNull(blockCache);
   }
+
+  @Test
+  public void testContinuesToScanIfHasMore() throws IOException {
+    // Conditions for this test to set up RegionScannerImpl to bail on the scan
+    // after a single iteration
+    // 1. Configure preadMaxBytes to something small to trigger scannerContext#returnImmediately
+    // 2. Configure a filter to filter out some rows, in this case rows with values < 5
+    // 3. Configure the filter's hasFilterRow to return true so RegionScannerImpl sets
+    // the limitScope to something with a depth of 0, so we bail on the scan after the first
+    // iteration
+
+    Configuration copyConf = new Configuration(conf);
+    copyConf.setLong(StoreScanner.STORESCANNER_PREAD_MAX_BYTES, 1);
+    Scan scan = new Scan();
+    scan.setFilter(new FiltersRowsLessThan5());
+    scan.setLimit(1);
+
+    try (Table table = TEST_UTIL.createTable(TABLE_NAME, FAM_NAME)) {
+      TableDescriptor htd = TEST_UTIL.getAdmin().getDescriptor(TABLE_NAME);
+      RegionInfo hri = TEST_UTIL.getAdmin().getRegions(TABLE_NAME).get(0);
+
+      for (int i = 0; i < 10; ++i) {
+        table.put(createPut(i));
+      }
+
+      // Flush contents to disk so we can scan the fs
+      TEST_UTIL.getAdmin().flush(TABLE_NAME);
+
+      ClientSideRegionScanner clientSideRegionScanner =
+        new ClientSideRegionScanner(copyConf, fs, rootDir, htd, hri, scan, null);
+      RegionScanner scannerSpy = spy(clientSideRegionScanner.scanner);
+      clientSideRegionScanner.scanner = scannerSpy;
+      Result result = clientSideRegionScanner.next();
+
+      verify(scannerSpy, times(6)).nextRaw(anyList());
+      assertNotNull(result);
+      assertEquals(Bytes.toInt(result.getRow()), 5);
+      assertTrue(clientSideRegionScanner.hasMore);
+
+      for (int i = 6; i < 10; ++i) {
+        result = clientSideRegionScanner.next();
+        verify(scannerSpy, times(i + 1)).nextRaw(anyList());
+        assertNotNull(result);
+        assertEquals(Bytes.toInt(result.getRow()), i);
+      }
+
+      result = clientSideRegionScanner.next();
+      assertNull(result);
+      assertFalse(clientSideRegionScanner.hasMore);
+    }
+  }
+
+  private static Put createPut(int rowAsInt) {
+    byte[] row = Bytes.toBytes(rowAsInt);
+    Put put = new Put(row);
+    put.addColumn(FAM_NAME, row, row);
+    return put;
+  }
+
+  private static class FiltersRowsLessThan5 extends FilterBase {
+
+    @Override
+    public boolean filterRowKey(Cell cell) {
+      byte[] rowKey = Arrays.copyOfRange(cell.getRowArray(), cell.getRowOffset(),
+        cell.getRowLength() + cell.getRowOffset());
+      int intValue = Bytes.toInt(rowKey);
+      return intValue < 5;
+    }
+
+    @Override
+    public boolean hasFilterRow() {
+      return true;
+    }
+  }
 }