loopback-component-changestreamer

The component observes a number specified models and notifies about the changes by SSE.

The main difference with Loopback /change-stream channels is that this implementation creates only two observers (after save and after delete) per model and then streams the changes to keep-alive registered connections. In contrast Loopback creates two same observers for each connection.

Install and Setup

Install the company: npm install --save loopback-component-changestreamer

Important! Disable compression middleware in middleware.json files like this:

{
  ...
  "compression": {
    "enabled":false
	},
	...
}

Add the following configuration to component-config.json:

{
  ...
  "loopback-component-changestreamer": {
    "mountPath": "/api/updates",
    "reconnectTimeout": 3000,
    "responseTimeout": 120000,
    "models": [
      "Foo",
      "Bar",
      "Baz"
    ],
    "headers": [
      "x-auth-request-user"
    ]
  },
  ...
}

See e2e/ directory as an example for how to make project configuration.

The configuration parameters:

• mountPath - base URL to subscribe for updates;
• reconnectTimeout - instruct Browser to reconnect after this timeout if connection is lost;
• responseTimeout - the response socket will be closed after this timeout;
• models - array of model names to observe.
  • headers - headers and values to embed in the stream metadata.

The component configuration above adds 3 middleware rules:

• GET "/api/updates" to connect some SourceEvent listener;
• GET "/api/updates/stat" to see a statistics about number of current connections;
• DELETE "/api/updates" to close all registered connections.

The following snippet can be used on client side to connect:

var src = new EventSource('//<host>:<port>/api/updates');
src.addEventListener('message', function(message) {
  ...
});