## What?
Prior to this commit, the `rabbitmq_event_exchange` internally published
always AMQP 0.9.1 messages to the `amq.rabbitmq.event` topic exchange.
This commit allows users to configure the plugin to publish AMQP 1.0
messages instead.
## Why?
Prior to this commit, when an AMQP 1.0 client consumed events,
event properties that are lists were omitted. For example property
`client_properties` of event `connection.created` or property
`arguments` of event `queue.created` were omitted because of the following sequence:
1. The event exchange plugins listens for all kind of internal events.
2. The event exchange plugin re-publishes all events as AMQP 0.9.1 message to the event exchange.
3. Later, when an AMQP 1.0 client consumes this message, the broker must translate the message from AMQP 0.9.1 to AMQP 1.0.
4. This translation follows the rules outlined in https://www.rabbitmq.com/docs/conversions#amqpl-amqp
5. Specifically, in this table the row before the last one describes the rule we're hitting here. It says that if the AMQP 0.9.1
header value is not an `x-` prefixed header and its value is an array or table, then this header is not converted.
That's because AMQP 1.0 application-properties must be simple types as mandated in https://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-application-properties
## How?
The user can configure the plugin as follows to have the plugin
internally publish AMQP 1.0 messages:
```
event_exchange.protocol = amqp_1_0
```
To support complex types such as lists, the plugin sets all event
properties as AMQP 1.0 message-annotations. The plugin prefixes all message
annotation keys with `x-opt-` to comply with the AMQP 1.0 spec.
## Alternative Design
An alternative design would have been to format all event properties
e.g. as JSON within the message body. However, this breaks routing on
specific event property values via a headers exchange.
## Documentation
https://github.com/rabbitmq/rabbitmq-website/pull/2129
This is the recommended way with Erlang.mk.
By default, the version is inherited from rabbitmq-server-release when
the source archive is created, or computed from git-describe(1) (see
`rabbitmq-components.mk`). One can override the version from the command
line by setting the `PROJECT_VERSION` variable.
[#130992027]
David Ansari
Loïc Hoguin
Philip Kuryloski
Jean-Sébastien Pédron
kjnilsson
Jean-Sébastien Pédron
Michael Klishin
Simon MacMullen