The problem

When using Outbox pattern to send messages to Pub/Sub - message could be sent more than once (in case of db failure). Every message then generates unique messageId creating duplicated messages on consumer side. And implementing custom deduplication mechanism for every consumer is not an option.

Feature request

To be able to publish messages with specified messageId (unique UUID) so that Pub/Sub can detect duplicates and feature 'Exactly once delivery' will work much better. messageId is already there, we just need a possibility to set it on the Publisher.PublishMessage() side.

How this might work

Pub/Sub can use messageId to deduplicate messages and consider every other message with same messageId as the same one (duplicate) and just ignore it.

Alternative solutions

• Deduplicating mechanism on consumer side using RDS Database. It's too complex to write for every consumer which needs to process message only once.
• Using Pub/Sub with Dataflow - only works with streaming pipelines with Pub/Sub and also too complex. (and how to use it with Cloud Functions for Firebase - I don't know).
• Azure Service Bus supports Duplicate Detection using Message ID Service Bus Duplicate Detection

Other information

• Here is a topic on Google Cloud Community where something similar was discussed Google Cloud Community Topic