cckellogg commented on a change in pull request #184: Dead letter queue implementation URL: https://github.com/apache/pulsar-client-go/pull/184#discussion_r378673068
########## File path: pulsar/dlq_router.go ########## @@ -0,0 +1,147 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +package pulsar + +import ( + "context" + "errors" + "time" + + "github.com/apache/pulsar-client-go/pulsar/internal" + log "github.com/sirupsen/logrus" +) + +type dlqRouter struct { + client Client + producer Producer + policy *DLQPolicy + messageCh chan ConsumerMessage + closeCh chan interface{} + log *log.Entry +} + +func newDlqRouter(client Client, policy *DLQPolicy) (*dlqRouter, error) { + r := &dlqRouter{ + client: client, + policy: policy, + } + + if policy != nil { + if policy.MaxDeliveries <= 0 { + return nil, errors.New("DLQPolicy.MaxDeliveries needs to be > 0") + } + + if policy.Topic == "" { + return nil, errors.New("DLQPolicy.Topic needs to be set to a valid topic name") + } + + r.messageCh = make(chan ConsumerMessage) + r.closeCh = make(chan interface{}) + r.log = log.WithField("dlq-topic", policy.Topic) + go r.run() + } + return r, nil +} + +func (r *dlqRouter) shouldSendToDlq(cm *ConsumerMessage) bool { + if r.policy == nil { + return false + } + + msg := cm.Message.(*message) + r.log.WithField("count", msg.redeliveryCount). + WithField("max", r.policy.MaxDeliveries). + WithField("msgId", msg.msgID). + Debug("Should route to DLQ?") + + // We use >= here because we're comparing the number of re-deliveries with + // the number of deliveries. So: + // * the user specifies that wants to process a message up to 10 times. + // * the first time, the redeliveryCount == 0, then 1 and so on + // * when we receive the message and redeliveryCount == 10, it means + // that the application has already got (and Nack()) the message 10 + // times, so this time we should just go to DLQ. + return cm.Message.(*message).redeliveryCount >= r.policy.MaxDeliveries +} + +func (r *dlqRouter) Chan() chan ConsumerMessage { + return r.messageCh +} + +func (r *dlqRouter) run() { + for { + select { + case cm := <-r.messageCh: + r.log.WithField("msgID", cm.ID()).Debug("Got message for DLQ") + producer := r.getProducer() + + msg := cm.Message.(*message) + msgID := msg.ID() + eventTime := msg.EventTime() + producer.SendAsync(context.Background(), &ProducerMessage{ + Payload: msg.Payload(), + Key: msg.Key(), + Properties: msg.Properties(), + EventTime: &eventTime, + ReplicationClusters: msg.replicationClusters, + }, func(MessageID, *ProducerMessage, error) { + r.log.WithField("msgID", msgID).Debug("Sent message to DLQ") + cm.Consumer.AckID(msgID) + }) + + case <-r.closeCh: + if r.producer != nil { + r.producer.Close() + } + r.log.Debug("Closed DLQ router") + return + } + } +} + +func (r *dlqRouter) close() { + if r.closeCh != nil { + r.closeCh <- nil Review comment: I think this could cause a deadlock for anything but a single topic because there will be multiple calls to close() and only the first call will be able to send on the closeCh because the go routine reading from the closeCh will exit. We could do something like this: ``` select { case r.closeCh <- nil: // this case will only occur when we can send on the channel default: // the closeCh is either nil or it's blocked and we can't send on it } ``` ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services
