s3: Don't set NextMarker when listing is not truncated (#7012)

Setting NextMarker when IsTruncated is not set seems to be confusing
AWS C++ SDK, this commit will avoid setting any string in NextMarker.

cmd/fs-v1.go

@@ -1212,9 +1212,8 @@ func (fs *FSObjects) ListObjects(ctx context.Context, bucket, prefix, marker, de
 		fs.listPool.Set(params, walkResultCh, endWalkCh)
 	}
 
-	result := ListObjectsInfo{IsTruncated: !eof}
+	result := ListObjectsInfo{}
 	for _, objInfo := range objInfos {
-		result.NextMarker = objInfo.Name
 		if objInfo.IsDir && delimiter == slashSeparator {
 			result.Prefixes = append(result.Prefixes, objInfo.Name)
 			continue
@@ -1222,6 +1221,13 @@ func (fs *FSObjects) ListObjects(ctx context.Context, bucket, prefix, marker, de
 		result.Objects = append(result.Objects, objInfo)
 	}
 
+	if !eof {
+		result.IsTruncated = true
+		if len(objInfos) > 0 {
+			result.NextMarker = objInfos[len(objInfos)-1].Name
+		}
+	}
+
 	// Success.
 	return result, nil
 }

cmd/object-api-listobjects_test.go

@@ -574,6 +574,14 @@ func testListObjects(obj ObjectLayer, instanceType string, t TestErrHandler) {
 				t.Errorf("Test %d: %s: Expected IsTruncated flag to be %v, but instead found it to be %v", i+1, instanceType, testCase.result.IsTruncated, result.IsTruncated)
 			}
 
+			if testCase.result.IsTruncated && result.NextMarker == "" {
+				t.Errorf("Test %d: %s: Expected NextContinuationToken to contain a string since listing is truncated, but instead found it to be empty", i+1, instanceType)
+			}
+
+			if !testCase.result.IsTruncated && result.NextMarker != "" {
+				t.Errorf("Test %d: %s: Expected NextContinuationToken to be empty since listing is not truncated, but instead found `%v`", i+1, instanceType, result.NextMarker)
+			}
+
 		}
 		// Take ListObject treeWalk go-routine to completion, if available in the treewalk pool.
 		if result.IsTruncated {

cmd/xl-v1-list-objects.go

@@ -130,15 +130,22 @@ func (xl xlObjects) listObjects(ctx context.Context, bucket, prefix, marker, del
 		xl.listPool.Set(params, walkResultCh, endWalkCh)
 	}
 
-	result := ListObjectsInfo{IsTruncated: !eof}
+	result := ListObjectsInfo{}
 	for _, objInfo := range objInfos {
-		result.NextMarker = objInfo.Name
 		if objInfo.IsDir && delimiter == slashSeparator {
 			result.Prefixes = append(result.Prefixes, objInfo.Name)
 			continue
 		}
 		result.Objects = append(result.Objects, objInfo)
 	}
+
+	if !eof {
+		result.IsTruncated = true
+		if len(objInfos) > 0 {
+			result.NextMarker = objInfos[len(objInfos)-1].Name
+		}
+	}
+
 	return result, nil
 }