CLDSRV-908: populate dataStoreETag on the CopyObject recompute path

The recompute path writes the destination through plain data.put, which
(unlike data.copyObject, used by the propagate path) does not return a
dataStoreETag, so the destination's location entry was stored without one.
Nothing breaks visibly — partNumber readers fall back to treating the copy
as a single part — but it left the recompute path as the only data-writing
path producing legacy ETag-less locations and dropped the written-bytes MD5
that integrity/audit tooling relies on.

Read the MD5 from data.put's hashedStream callback argument (completedHash,
which the arsenal wrapper guarantees is set before the callback fires) and
stamp the location as 1:<md5>, matching createAndStoreObject. Falls back to
dataRetrievalInfo.dataStoreETag for external backends. Adds a unit test
asserting the recomputed destination location carries the 1:-prefixed MD5.

Author: leif-scality

lib/api/objectCopy.js

@@ -234,7 +234,7 @@ function _recomputeChecksumAndStore(log, request, requestedAlgo, sourceObjMD, da
     const doPut = cipherBundle => data.put(
         cipherBundle, checksumStream, storeMetadataParams.size,
         dataStoreContext, backendInfoDest, log,
-        (err, dataRetrievalInfo) => {
+        (err, dataRetrievalInfo, hashedStream) => {
             if (err) {
                 return done(err);
             }
@@ -244,13 +244,16 @@ function _recomputeChecksumAndStore(log, request, requestedAlgo, sourceObjMD, da
                 value: checksumStream.digest,
                 type: 'FULL_OBJECT',
             };
+            // Prefix the part number like createAndStoreObject does, so
+            // partNumber-based reads see the copy as a single-part object.
+            const dataStoreETag = dataRetrievalInfo.dataStoreETag || hashedStream?.completedHash;
             const putResult = {
                 key: dataRetrievalInfo.key,
                 size: storeMetadataParams.size,
                 start: 0,
                 dataStoreName: dataRetrievalInfo.dataStoreName,
                 dataStoreType: dataRetrievalInfo.dataStoreType,
-                dataStoreETag: dataRetrievalInfo.dataStoreETag,
+                dataStoreETag: dataStoreETag ? `1:${dataStoreETag}` : undefined,
                 dataStoreVersionId:
                     dataRetrievalInfo.dataStoreVersionId,
             };

tests/unit/api/objectCopy.js

@@ -1,5 +1,6 @@
 const assert = require('assert');
 const async = require('async');
+const crypto = require('crypto');
 const { Readable } = require('stream');
 const { storage, versioning } = require('arsenal');
 const sinon = require('sinon');
@@ -974,6 +975,25 @@ describe('objectCopy checksum recompute', () => {
         }, done);
     });
 
+    it('should store a part-prefixed dataStoreETag on the recomputed destination location', done => {
+        // The recompute path writes the destination through data.put, which
+        // does not return a dataStoreETag; it must be filled in from the MD5
+        // of the streamed bytes, prefixed like createAndStoreObject does.
+        const expectedMD5 = crypto.createHash('md5').update(objData[0]).digest('hex');
+        const req = _createObjectCopyRequest(destBucketName, {
+            'x-amz-checksum-algorithm': 'SHA256',
+        });
+        objectCopy(authInfo, req, sourceBucketName, objectKey, undefined, log, err => {
+            assert.ifError(err);
+            metadata.getObjectMD(destBucketName, objectKey, {}, log, (err, md) => {
+                assert.ifError(err);
+                assert.strictEqual(md.location[0].dataStoreETag, `1:${expectedMD5}`,
+                    'recomputed destination location should carry a 1:-prefixed MD5 dataStoreETag');
+                done();
+            });
+        });
+    });
+
     it('should reject an unknown x-amz-checksum-algorithm value with InvalidRequest', done => {
         const req = _createObjectCopyRequest(destBucketName, {
             'x-amz-checksum-algorithm': 'GARBAGE',