HADOOP-18355. Update previous index properly while validating overlapping ranges. (#4647)

part of HADOOP-18103.

Contributed By: Mukund Thakur

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/VectoredReadUtils.java

@@ -210,6 +210,7 @@ public final class VectoredReadUtils {
       if (sortedRanges[i].getOffset() < prev.getOffset() + prev.getLength()) {
         throw new UnsupportedOperationException("Overlapping ranges are not supported");
       }
+      prev = sortedRanges[i];
     }
     return Arrays.asList(sortedRanges);
   }

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/TestVectoredReadUtils.java

@@ -35,6 +35,8 @@ import org.apache.hadoop.fs.impl.CombinedFileRange;
 import org.apache.hadoop.test.HadoopTestBase;
 
 import static org.apache.hadoop.fs.VectoredReadUtils.sortRanges;
+import static org.apache.hadoop.fs.VectoredReadUtils.validateNonOverlappingAndReturnSortedRanges;
+import static org.apache.hadoop.test.LambdaTestUtils.intercept;
 import static org.apache.hadoop.test.MoreAsserts.assertFutureCompletedSuccessfully;
 import static org.apache.hadoop.test.MoreAsserts.assertFutureFailedExceptionally;
 
@@ -231,6 +233,36 @@ public class TestVectoredReadUtils extends HadoopTestBase {
 
   }
 
+  @Test
+  public void testValidateOverlappingRanges()  throws Exception {
+    List<FileRange> input = Arrays.asList(
+            FileRange.createFileRange(100, 100),
+            FileRange.createFileRange(200, 100),
+            FileRange.createFileRange(250, 100)
+    );
+
+    intercept(UnsupportedOperationException.class,
+        () -> validateNonOverlappingAndReturnSortedRanges(input));
+
+    List<FileRange> input1 = Arrays.asList(
+            FileRange.createFileRange(100, 100),
+            FileRange.createFileRange(500, 100),
+            FileRange.createFileRange(1000, 100),
+            FileRange.createFileRange(1000, 100)
+    );
+
+    intercept(UnsupportedOperationException.class,
+        () -> validateNonOverlappingAndReturnSortedRanges(input1));
+
+    List<FileRange> input2 = Arrays.asList(
+            FileRange.createFileRange(100, 100),
+            FileRange.createFileRange(200, 100),
+            FileRange.createFileRange(300, 100)
+    );
+    // consecutive ranges should pass.
+    validateNonOverlappingAndReturnSortedRanges(input2);
+  }
+
   @Test
   public void testMaxSizeZeroDisablesMering() throws Exception {
     List<FileRange> randomRanges = Arrays.asList(