Custom Steps

Your app can use the function() method to listen to incoming custom step requests. Custom steps are used in Workflow Builder to build workflows. The method requires a step callback_id of type string. This callback_id must also be defined in your Function definition. Custom steps must be finalized using the complete() or fail() listener arguments to notify Slack that your app has processed the request.

• complete() requires one argument: an outputs object. It ends your custom step successfully and provides an object containing the outputs of your custom step as per its definition.
• fail() requires one argument: error of type string. It ends your custom step unsuccessfully and provides a message containing information regarding why your custom step failed.

You can reference your custom step's inputs using the getInputs() method shown below.

app.function("sample_function", (req, ctx) -> {
  app.executorService().submit(() -> {
    try {
      String userId = req.getEvent().getInputs().get("user_id").asString();
      ChatPostMessageResponse response = ctx.client().chatPostMessage(r -> r
        .channel(userId) // sending a DM
        .text("Hi! Thank you for submitting the request! We'll let you know once the processing completes.")
      );
      Map<String, Object> outputs = new HashMap<String, Object>();
      outputs.put("channel_id", response.getChannel());
      outputs.put("ts", response.getTs());
      ctx.complete(outputs);
    } catch (Exception e) {
      ctx.logger.error(e.getMessage(), e);
      try {
        ctx.fail("Failed to handle 'sample_function' custom step execution (error: " + e.getMessage() + ")");
      } catch (Exception ex) {
        ctx.logger.error(e.getMessage(), e);
      }
    }
  });
  return ctx.ack();
});

The corresponding function definition section of the app manifest for the preceding function might look like this:

...
"functions": {
    "sample_function": {
        "title": "Send a request",
        "description": "Send some request to the backend",
        "input_parameters": {
            "user_id": {
                "type": "slack#/types/user_id",
                "title": "User",
                "description": "Who to send it",
                "is_required": true,
                "hint": "Select a user in the workspace",
                "name": "user_id"
            }
        },
        "output_parameters": {
            "channel_id": {
                "type": "slack#/types/channel_id",
                "title": "DM ID",
                "description": "The DM ID",
                "is_required": true,
                "name": "channel_id"
            },
            "ts": {
                "type": "string",
                "title": "Message timestamp",
                "description": "Sent message timestamp",
                "is_required": true,
                "name": "ts"
            }
        }
    }
}

Once your custom step is defined in your app's manifest and implemented in code, it is discoverable in Workflow Builder when you Add Step and search for the title of your step or name of your app.