@embr-modules/event-stream

Embr Event Stream Module

An Ignition module that provides an API for high-speed streaming of tag changes and alarm events via SSE (server-sent events).

Server-Sent Events (SSE) is a server push technology enabling a client to receive automatic updates from a server via an HTTP connection. All modern browsers support server-sent events: Firefox 6+, Google Chrome 6+, Opera 11.5+, Safari 5+, Microsoft Edge 79+.

Getting Started

1. Download the latest version from releases.
2. Install the module through the Ignition Gateway web interface.

Module Documentation

• #TODO Module documentation

Gateway API

• Create a EventStream Session : POST /embr/tag/stream/session
• Subscribe to a EventStream Session : GET /embr/tag/stream/session/{session_id}

---

Create a EventStream Session

Creates a EventStream session containing the specified tags. The returned session_id is used to access the stream.

As a security measure, the session_id is time-limited and single use. If the session is not accessed within 30 seconds after creation, a time-out occurs and the session is discarded. Only a single client may access a given session_id.

Item	Value
URL	/embr/tag/stream/session
Method	POST
Body	{ tagPaths: [] }
Auth	body

Body Example

{
  "username": "admin",
  "password": "password",
  "tag_paths": [
    "[default]Tag1",
    "[default]Path/Tag2"
  ]
}

Success Response

Code : 200 OK

The response is a JSON object containing the session_id of the stream and details of the tags included in the session.

Each tag is given a numeric tag_id in order to compress the event source message size. The EventSource messages will use this tag_id when sending tag change information.

{
  "status": "success",
  "data": {
    "session_id": "8c1a5b02-df33-4a2e-ad6f-101f76ab3d06",
    "tags": [
      {
        "tag_path": "[default]Tag1",
        "alarm_path": "prov:default:/tag:Tag1",
        "tag_id": 0
      },
      {
        "tag_path": "[default]Path/Tag2",
        "alarm_path": "prov:default:/tag:Path/Tag2",
        "tag_id": 1
      }
    ]
  }
}

---

Subscribe to a EventStream Session

Subscribe to a EventStream by its session_id. This endpoint is meant to be accessed by an EventSource. For more details, see Mozilla's MDN WebDocs.

Item	Value
URL	/embr/tag/stream/session/{session_id}
Method	GET
Params	session_id: EventStream session id
Auth	None

Success Response

Code : 200 OK

Messages events have the following format:

event: tag_change
data: {"tag_id":0,"v":"Tag Value!","q": 192,"t":1717624491517}

event: alarm_event
data: {"tag_id":0,"count":1,"displayPath":"","eventData":{"eventValue":"false","name":"AlarmName","eventTime":"Thu Jun 20 13:17:37 EDT 2024","priority":"Critical","displayPath":""},"extension":{"isShelved":"false"},"id":"454d77c5-44f8-4e52-ab3c-e1ed5c950583","isAcked":false,"isCleared":false,"isShelved":false,"label":"AlarmName","name":"AlarmName","notes":"","priority":"Critical","source":"prov:default:/tag:Tag1:/alm:AlarmName","state":"Active, Unacknowledged","values":[{"isShelved":"false"}]}

---

Changelog

The changelog is regularly updated to reflect what's changed in each new release.

Copyright and Licensing

Copyright (C) 2023 Musson Industrial

Free use of this software is granted under the terms of the MIT License.