syncObject: delete 'coms-id' tag on new file if id already in use

app/src/services/sync.js

@@ -175,7 +175,43 @@ const service = {
 
         // Case: not in COMS - insert new COMS object
         else {
-          const objId = await service._deriveObjectId(s3Object, path, bucketId);
+          let objId = await service._deriveObjectId(s3Object, path, bucketId);
+          let existingComsId;
+          try {
+            existingComsId = await objectService.read(objId);
+          } catch {
+            // Derived object id not currently in use by COMS
+          }
+
+          // Object id in 'coms-id' S3 tag already in use in COMS:
+          //  Delete the 'coms-id' tag on the new object,
+          //  so that we don't attempt to re-use an existing COMS object id.
+          if (existingComsId) {
+            const sourceObject = await storageService.getObjectTagging({
+              filePath: path,
+              bucketId: bucketId
+            });
+
+            // Workaround for deleting just the 'coms-id' tag (S3 can only delete ALL tags on an object):
+            // Retrieve all tags, delete all tags on object, then re-add all tags except 'coms-id'.
+            const objectTags = sourceObject.TagSet.filter(
+              x => !sourceObject.TagSet.includes(x.Key) && x.Key != 'coms-id'
+            );
+            await storageService.deleteObjectTagging({
+              filePath: path,
+              bucketId: bucketId
+            });
+            const data = {
+              bucketId,
+              filePath: path,
+              tags: objectTags
+            };
+            await storageService.putObjectTagging(data);
+
+            // _deriveObjectId() doesn't care if it conflicts with existing coms-id's,
+            // so generate a new one after deleting the S3 tag
+            objId = uuidv4();
+          }
 
           response = await objectService.create({
             id: objId,