Mercure Message Binding v0.1.0

The Mercure message binding describes the data payload that is sent as part of a Server-Sent Event (SSE) from the Mercure Hub.

Overview

In Mercure, the message is the data field of the POST request sent to the Hub. This content is then pushed to subscribers inside the data field of an SSE. This binding is used on an AsyncAPI message object to indicate that its payload represents this data. As of v0.1.0, this binding is a placeholder and has no configurable properties. Its purpose is purely informational.

Message Properties

Property	Type	Required	Description
bindingVersion	string	No	Binding version (defaults to 0.1.0)

Mercure Message Concepts

The data Field

The core of a Mercure update is the data parameter. This is typically a string, often formatted as JSON, but it can be any text-based content. The Mercure Hub takes this data and wraps it in an SSE structure.

A simple data string like {"message": "hello"} becomes an SSE event like this:

id: urn:uuid:c32f8429-f442-4217-9166-5868a85c4a16
data: {"message": "hello"}

Private vs. Public Updates

While not a property of the message payload itself, it's important to know that the publisher can mark an update as private. This tells the Hub to only deliver the message to subscribers who have presented a valid JSON Web Token (JWT) authorizing them to receive it. The message content itself is not encrypted by Mercure.

Example

This example defines a message that could be published to a Mercure topic.

messages:
  userUpdate:
    summary: An update about a user's profile.
    payload:
      type: object
      properties:
        id:
          type: string
          description: The user's ID.
        newStatus:
          type: string
          description: The new status of the user.
    bindings:
      mercure:
        bindingVersion: '0.1.0'

When published, the payload object would be serialized (e.g., to a JSON string) and sent as the data parameter in the POST request to the Mercure Hub.

Changelog

Version 0.1.0

• Initial release of the Mercure message binding.
• The binding is a placeholder with no specific properties, serving to identify the message payload as the data for a Mercure SSE event.