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Websocket triggers

Windmill can connect to websocket servers and trigger runnables (scripts, flows) when a message is received. Listening is done from the servers, so it doesn't take up any workers. Websocket triggers are not available on the Cloud.

How to use​

Create a new trigger on the Websocket triggers page. Specify the URL of the websocket server. Instead of a static URL, you can also specify a script or flow to return the connect URL. This is useful when you need to pass an authentication query parameter to the connect URL. The runnable must return a string.

Websocket URL and runnable

Websocket URL as runnable result

Once the URL set, select the runnable that should be triggered by this trigger. The received webhook message will be passed to the runnable as a string argument called msg. If you use a preprocessor, the wm_trigger object will be of the form:

{
  "kind": "websocket",
  "websocket": {
    "url": "ws://my.websocket.server",
  }
}

The trigger also supports additional configuration options:

Initial messages​

You can specify a list of initial messages to send to the websocket server when connection to the server is established. This is useful for authentication or subscription messages. They can be static strings or runnables that return the message. The static string field is in JSON format and will be stringified before sending. If the JSON value is a string, it will be sent without the wrapping quotes. The runnable can return a string or a JSON object, which will be stringified before sending. The messages are sent in the order they are specified.

Initial messages

Filters​

Instead of having all messages trigger the runnable, you can specify filters to only trigger the runnable when the message matches all filters. Windmill supports the following filter:

  • JSON: The message is parsed as a JSON object and the filter checks that the filter key exists and the value at the key is equal or is a subset of the filter value.

Filters