| // Copyright 2020 Google LLC |
| // |
| // Licensed 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 |
| // |
| // https://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 |
| |
| package pubsub |
| |
| import ( |
| "time" |
| ) |
| |
| // AckHandler implements ack/nack handling. |
| type AckHandler interface { |
| // OnAck processes a message ack. |
| OnAck() |
| |
| // OnNack processes a message nack. |
| OnNack() |
| } |
| |
| // Message represents a Pub/Sub message. |
| type Message struct { |
| // ID identifies this message. This ID is assigned by the server and is |
| // populated for Messages obtained from a subscription. |
| // |
| // This field is read-only. |
| ID string |
| |
| // Data is the actual data in the message. |
| Data []byte |
| |
| // Attributes represents the key-value pairs the current message is |
| // labelled with. |
| Attributes map[string]string |
| |
| // PublishTime is the time at which the message was published. This is |
| // populated by the server for Messages obtained from a subscription. |
| // |
| // This field is read-only. |
| PublishTime time.Time |
| |
| // DeliveryAttempt is the number of times a message has been delivered. |
| // This is part of the dead lettering feature that forwards messages that |
| // fail to be processed (from nack/ack deadline timeout) to a dead letter topic. |
| // If dead lettering is enabled, this will be set on all attempts, starting |
| // with value 1. Otherwise, the value will be nil. |
| // This field is read-only. |
| DeliveryAttempt *int |
| |
| // OrderingKey identifies related messages for which publish order should |
| // be respected. If empty string is used, message will be sent unordered. |
| OrderingKey string |
| |
| // ackh handles Ack() or Nack(). |
| ackh AckHandler |
| } |
| |
| // Ack indicates successful processing of a Message passed to the Subscriber.Receive callback. |
| // It should not be called on any other Message value. |
| // If message acknowledgement fails, the Message will be redelivered. |
| // Client code must call Ack or Nack when finished for each received Message. |
| // Calls to Ack or Nack have no effect after the first call. |
| func (m *Message) Ack() { |
| if m.ackh != nil { |
| m.ackh.OnAck() |
| } |
| } |
| |
| // Nack indicates that the client will not or cannot process a Message passed to the Subscriber.Receive callback. |
| // It should not be called on any other Message value. |
| // Nack will result in the Message being redelivered more quickly than if it were allowed to expire. |
| // Client code must call Ack or Nack when finished for each received Message. |
| // Calls to Ack or Nack have no effect after the first call. |
| func (m *Message) Nack() { |
| if m.ackh != nil { |
| m.ackh.OnNack() |
| } |
| } |
| |
| // NewMessage creates a message with an AckHandler implementation, which should |
| // not be nil. |
| func NewMessage(ackh AckHandler) *Message { |
| return &Message{ackh: ackh} |
| } |
| |
| // MessageAckHandler provides access to the internal field Message.ackh. |
| func MessageAckHandler(m *Message) AckHandler { |
| return m.ackh |
| } |