Refine err msg in SetOffsetAt() (#1001)

Author: haorenfsa

reader.go

@@ -1083,12 +1083,16 @@ func (r *Reader) SetOffsetAt(ctx context.Context, t time.Time) error {
 	}
 	r.mutex.Unlock()
 
+	if len(r.config.Brokers) < 1 {
+		return errors.New("no brokers in config")
+	}
+	var conn *Conn
+	var err error
 	for _, broker := range r.config.Brokers {
-		conn, err := r.config.Dialer.DialLeader(ctx, "tcp", broker, r.config.Topic, r.config.Partition)
+		conn, err = r.config.Dialer.DialLeader(ctx, "tcp", broker, r.config.Topic, r.config.Partition)
 		if err != nil {
 			continue
 		}
-
 		deadline, _ := ctx.Deadline()
 		conn.SetDeadline(deadline)
 		offset, err := conn.ReadOffset(t)
@@ -1099,7 +1103,7 @@ func (r *Reader) SetOffsetAt(ctx context.Context, t time.Time) error {
 
 		return r.SetOffset(offset)
 	}
-	return fmt.Errorf("error setting offset for timestamp %+v", t)
+	return fmt.Errorf("error dialing all brokers, one of the errors: %w", err)
 }
 
 // Stats returns a snapshot of the reader stats since the last time the method