upstream-watermill/docs/content/development/pub-sub-implementing.md

+++ title = "Implementing a new Pub/Sub" description = "Bring Your Own Pub/Sub" date = 2018-12-05T12:48:34+01:00 weight = 200 draft = false bref = "Bring Your Own Pub/Sub" +++

The Pub/Sub interface

To add support for a custom Pub/Sub, you have to implement both message.Publisher and message.Subscriber interfaces.

{{% load-snippet-partial file="src-link/message/pubsub.go" first_line_contains="type Publisher interface" last_line_contains="type SubscribeInitializer" padding_after="0" %}}

Testing

Watermill provides a set of test scenarios that any Pub/Sub implementation can use. Each test suite needs to declare what features it supports and how to construct a new Pub/Sub. These scenarios check both basic usage and more uncommon use cases. Stress tests are also included.

TODO list

Here are a few things you shouldn't forget about:

1. Logging (good messages and proper levels).
2. Replaceable and configurable message marshaler.
3. Close() implementation for the publisher and subscriber that is:
   • idempotent
   • working correctly even when the publisher or the subscriber is blocked (for example, waiting for an Ack).
   • working correctly when the subscriber output channel is blocked (because nothing is listening on it).
4. Ack() and Nack() support for consumed messages.
5. Redelivery on Nack() for a consumed message.
6. Use [Universal Pub/Sub tests]({{< ref "/docs/pub-sub#universal-tests" >}}). For debugging tips, you should check tests troubleshooting guide.
7. Performance optimizations.
8. GoDocs, [Markdown docs]({{< ref "/pubsubs" >}}) and Getting Started examples.

We will also be thankful for submitting a pull request with the new Pub/Sub implementation.

If anything is not clear, feel free to use any of our [support channels]({{< ref "/support" >}}) to reach us, we will be glad to help.