feat: add N5Writer.deleteBlock

* that deletes blocks or chunks

Author: bogovicj

src/main/java/org/janelia/saalfeldlab/n5/GsonKeyValueN5Writer.java

@@ -319,6 +319,16 @@ default boolean remove(final String path) throws N5Exception {
 		return true;
 	}
 
+	@Override
+	default boolean deleteBlock(
+			final String path,
+			final DatasetAttributes datasetAttributes,
+			final long... gridPosition) throws N5Exception {
+
+		final PositionValueAccess posKva = PositionValueAccess.fromKva(getKeyValueAccess(), getURI(), N5URI.normalizeGroupPath(path), datasetAttributes);
+		return posKva.remove(gridPosition);
+	}
+
 	@Override
 	default boolean deleteChunk(
 			final String path,

src/main/java/org/janelia/saalfeldlab/n5/N5Writer.java

@@ -384,6 +384,37 @@ default <T> void writeRegion(
 			});
 		}
 	}
+	
+	/**
+	 * Deletes the block at {@code gridPosition}.
+	 *
+	 * @param datasetPath dataset path
+	 * @param gridPosition position of block to be deleted
+	 * @throws N5Exception if the block exists but could not be deleted
+	 *
+	 * @return {@code true} if the block at {@code gridPosition} existed and was deleted.
+	 */
+	default boolean deleteBlock(
+			final String datasetPath,
+			final long... gridPosition) throws N5Exception {
+		final DatasetAttributes datasetAttributes = getDatasetAttributes(datasetPath);
+		return deleteBlock(datasetPath, datasetAttributes, gridPosition);
+	}
+
+	/**
+	 * Deletes the block at {@code gridPosition}.
+	 *
+	 * @param datasetPath the dataset path
+	 * @param datasetAttributes the dataset attributes
+	 * @param gridPosition position of block to be deleted
+	 * @throws N5Exception if the block exists but could not be deleted
+	 *
+	 * @return {@code true} if the block at {@code gridPosition} existed and was deleted.
+	 */
+	boolean deleteBlock(
+			String datasetPath,
+			DatasetAttributes datasetAttributes,
+			long... gridPosition) throws N5Exception;
 
 	/**
 	 * Deletes the chunk at {@code gridPosition}.

src/test/java/org/janelia/saalfeldlab/n5/AbstractN5Test.java

@@ -1307,9 +1307,16 @@ public void testDelete() {
 			assertTrue(readBlock instanceof ByteArrayDataBlock);
 			assertArrayEquals(byteBlock, ((ByteArrayDataBlock)readBlock).getData());
 
-			assertTrue("deleting existing block should return true", n5.deleteChunk(datasetName, position1));
-			assertFalse("deleting non-existing block should return false", n5.deleteChunk(datasetName, position1));
-			assertFalse("deleting non-existing block should return false", n5.deleteChunk(datasetName, position2));
+			assertTrue("deleting existing chunk should return true", n5.deleteChunk(datasetName, position1));
+			assertFalse("deleting non-existing chunk should return false", n5.deleteChunk(datasetName, position1));
+			assertFalse("deleting non-existing chunk should return false", n5.deleteChunk(datasetName, position2));
+
+			// for an unsharded dataset, deleteChunk and deleteBlock behave identically
+			assertFalse("deleting non-existing block should return false", n5.deleteBlock(datasetName, position1));
+			assertFalse("deleting non-existing block should return false", n5.deleteBlock(datasetName, position2));
+
+			n5.writeChunk(datasetName, attributes, dataBlock);
+			assertTrue("deleting existing block should return true", n5.deleteBlock(datasetName, position1));
 
 			// no block should exist anymore
 			assertNull(n5.readChunk(datasetName, attributes, position1));

src/test/java/org/janelia/saalfeldlab/n5/shard/ShardTest.java

@@ -58,6 +58,7 @@
 
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
@@ -425,10 +426,10 @@ public void writeReadShardTest() {
 			final int[] shardSize = new int[] {4,4};
 			final int shardN = 16;
 
-			final int[] blockSize = new int[] {2,2};
+			final int[] chunkSize = new int[] {2,2};
 
 			final String dataset = "writeReadShard";
-			DatasetAttributes attrs = getTestAttributes(DataType.INT32, new long[]{8, 8}, shardSize, blockSize);
+			DatasetAttributes attrs = getTestAttributes(DataType.INT32, new long[]{8, 8}, shardSize, chunkSize);
 
 			final int[] shardData = range(shardN);
 			IntArrayDataBlock shard = new IntArrayDataBlock(shardSize, new long[]{0, 0}, shardData);
@@ -475,6 +476,20 @@ public void writeReadShardTest() {
 					Stream.of( new long[] {0,0}, new long[] {1,0}, new long[] {0,1}).collect(Collectors.toList()));
 
 			assertNull(n5.readBlock(dataset, attrs, 0, 0));
+
+
+			// write the shard again
+			n5.writeBlock(dataset, attrs, shard);
+
+			// delete the block
+			// ensure it returns true because the block exists
+			assertTrue(n5.deleteBlock(dataset, attrs, shard.getGridPosition()));
+
+			// ensure it returns false when the block does not exist
+			assertFalse(n5.deleteBlock(dataset, attrs, shard.getGridPosition()));
+
+			// readBlock must return null for the deleted block
+			assertNull(n5.readBlock(dataset, attrs, shard.getGridPosition()));
 		}
 	}