Add single drive support for directory prefixes in Listing (#13829)

This fixes the compatibility issue with Hadoop 3.3.1

fixes #13710

cmd/object-api-common.go

@@ -247,6 +247,21 @@ func listObjects(ctx context.Context, obj ObjectLayer, bucket, prefix, marker, d
 		return loi, nil
 	}
 
+	if len(prefix) > 0 && maxKeys == 1 && delimiter == "" && marker == "" {
+		// Optimization for certain applications like
+		// - Cohesity
+		// - Actifio, Splunk etc.
+		// which send ListObjects requests where the actual object
+		// itself is the prefix and max-keys=1 in such scenarios
+		// we can simply verify locally if such an object exists
+		// to avoid the need for ListObjects().
+		objInfo, err := obj.GetObjectInfo(ctx, bucket, prefix, ObjectOptions{NoLock: true})
+		if err == nil {
+			loi.Objects = append(loi.Objects, objInfo)
+			return loi, nil
+		}
+	}
+
 	// For delimiter and prefix as '/' we do not list anything at all
 	// since according to s3 spec we stop at the 'delimiter'
 	// along // with the prefix. On a flat namespace with 'prefix'
@@ -290,6 +305,13 @@ func listObjects(ctx context.Context, obj ObjectLayer, bucket, prefix, marker, d
 		i := i
 		walkResult, ok := <-walkResultCh
 		if !ok {
+			if HasSuffix(prefix, SlashSeparator) {
+				objInfo, err := obj.GetObjectInfo(ctx, bucket, prefix, ObjectOptions{NoLock: true})
+				if err == nil {
+					loi.Objects = append(loi.Objects, objInfo)
+					return loi, nil
+				}
+			}
 			// Closed channel.
 			eof = true
 			break