refactor blobpart logic into a separate method and add unit tests.

Signed-off-by: Rishikesh1159 <[email protected]>

server/src/main/java/org/opensearch/index/store/remote/file/OnDemandBlockSnapshotIndexInput.java

@@ -138,16 +138,27 @@ protected IndexInput fetchBlock(int blockId) throws IOException {
         final long blockStart = getBlockStart(blockId);
         final long blockEnd = blockStart + getActualBlockSize(blockId);
 
+        // Block may be present on multiple chunks of a file, so we need
+        // to fetch each chunk/blob part separately to fetch an entire block.
+        BlobFetchRequest blobFetchRequest = BlobFetchRequest.builder()
+            .blobParts(getBlobParts(blockStart, blockEnd))
+            .directory(directory)
+            .fileName(blockFileName)
+            .build();
+        return transferManager.fetchBlob(blobFetchRequest);
+    }
+
+    /**
+     * Returns list of blob parts/chunks in a file for a given block.
+     */
+    protected List<BlobFetchRequest.BlobPart> getBlobParts(long blockStart, long blockEnd) {
         // If the snapshot file is chunked, we must account for this by
         // choosing the appropriate file part and updating the position
         // accordingly.
         int partNum = (int) (blockStart / partSize);
         long pos = blockStart;
         long diff = (blockEnd - blockStart);
 
-        // Block may be present on multiple chunks of a file, so we need
-        // to make multiple blobFetchRequest to fetch an entire block.
-        // Each fetchBlobRequest can fetch only a single chunk of a file.
         List<BlobFetchRequest.BlobPart> blobParts = new ArrayList<>();
         while (diff > 0) {
             long partStart = pos % partSize;
@@ -163,8 +174,7 @@ protected IndexInput fetchBlock(int blockId) throws IOException {
             pos = pos + fetchBytes;
             diff = (blockEnd - pos);
         }
-        BlobFetchRequest.Builder builder = BlobFetchRequest.builder().blobParts(blobParts).directory(directory).fileName(blockFileName);
-        return transferManager.fetchBlob(builder.build());
+        return blobParts;
     }
 
     @Override

server/src/main/java/org/opensearch/index/store/remote/utils/BlobFetchRequest.java

@@ -29,11 +29,14 @@ public class BlobFetchRequest {
 
     private final List<BlobPart> blobParts;
 
+    private final long blobLength;
+
     private BlobFetchRequest(Builder builder) {
         this.fileName = builder.fileName;
         this.filePath = builder.directory.getDirectory().resolve(fileName);
         this.directory = builder.directory;
         this.blobParts = builder.blobParts;
+        this.blobLength = builder.blobParts.stream().mapToLong(o -> o.getLength()).sum();
     }
 
     public Path getFilePath() {
@@ -52,6 +55,10 @@ public List<BlobPart> blobParts() {
         return blobParts;
     }
 
+    public long getBlobLength() {
+        return blobLength;
+    }
+
     public static Builder builder() {
         return new Builder();
     }

server/src/main/java/org/opensearch/index/store/remote/utils/TransferManager.java

@@ -159,11 +159,7 @@ public IndexInput getIndexInput() throws IOException {
 
         @Override
         public long length() {
-            long length = 0;
-            for (BlobFetchRequest.BlobPart blobPart : request.blobParts()) {
-                length += blobPart.getLength();
-            }
-            return length;
+            return request.getBlobLength();
         }
 
         @Override

server/src/test/java/org/opensearch/index/store/remote/file/OnDemandBlockSnapshotIndexInputTests.java

@@ -115,6 +115,7 @@ private void runAllTestsFor(int blockSizeShift) throws Exception {
         TestGroup.testGetBlock(blockedSnapshotFile, blockSize, FILE_SIZE);
         TestGroup.testGetBlockOffset(blockedSnapshotFile, blockSize, FILE_SIZE);
         TestGroup.testGetBlockStart(blockedSnapshotFile, blockSize);
+        TestGroup.testGetBlobParts(blockedSnapshotFile);
         TestGroup.testCurrentBlockStart(blockedSnapshotFile, blockSize);
         TestGroup.testCurrentBlockPosition(blockedSnapshotFile, blockSize);
         TestGroup.testClone(blockedSnapshotFile, blockSize);
@@ -252,6 +253,35 @@ public static void testGetBlockStart(OnDemandBlockSnapshotIndexInput blockedSnap
             assertEquals(blockSize * 2, blockedSnapshotFile.getBlockStart(2));
         }
 
+        public static void testGetBlobParts(OnDemandBlockSnapshotIndexInput blockedSnapshotFile) {
+            // block id 0
+            int blockId = 0;
+            long blockStart = blockedSnapshotFile.getBlockStart(blockId);
+            long blockEnd = blockStart + blockedSnapshotFile.getActualBlockSize(blockId);
+            assertEquals(
+                (blockEnd - blockStart),
+                blockedSnapshotFile.getBlobParts(blockStart, blockEnd).stream().mapToLong(o -> o.getLength()).sum()
+            );
+
+            // block 1
+            blockId = 1;
+            blockStart = blockedSnapshotFile.getBlockStart(blockId);
+            blockEnd = blockStart + blockedSnapshotFile.getActualBlockSize(blockId);
+            assertEquals(
+                (blockEnd - blockStart),
+                blockedSnapshotFile.getBlobParts(blockStart, blockEnd).stream().mapToLong(o -> o.getLength()).sum()
+            );
+
+            // block 2
+            blockId = 2;
+            blockStart = blockedSnapshotFile.getBlockStart(blockId);
+            blockEnd = blockStart + blockedSnapshotFile.getActualBlockSize(blockId);
+            assertEquals(
+                (blockEnd - blockStart),
+                blockedSnapshotFile.getBlobParts(blockStart, blockEnd).stream().mapToLong(o -> o.getLength()).sum()
+            );
+        }
+
         public static void testCurrentBlockStart(OnDemandBlockSnapshotIndexInput blockedSnapshotFile, int blockSize) throws IOException {
             // block 0
             blockedSnapshotFile.seek(blockSize - 1);