Webhook triggers

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Invoke a workflow when a specific URL receives a POST request

Webhook triggers are an automatic type of trigger that listens for a certain type of data, much like event triggers.

While event triggers are used for activating a trigger based on internal activity, webhooks are instead used when activating a trigger based on external activity. In other words, webhook triggers are useful when tying Slack functionality together with non-Slack services.

There are two steps to using a webhook trigger:

  1. Create a trigger, either via the CLI or at runtime
  2. Invoke the trigger with a POST Request

Create a webhook trigger

Triggers can be added to workflows in two ways:

  • You can add triggers with the CLI. These static triggers are created only once. You create them with the Slack CLI, attach them to your app's workflow, and that's that. The trigger is defined within a trigger file.

  • You can add triggers at runtime. These dynamic triggers are created at any step of a workflow so they can incorporate data acquired from other workflow steps. The trigger is defined within a function file.

Slack CLI built-in documentation
Use slack trigger --help to easily access information on the trigger command's flags and subcommands.

The triggers you create when running locally (with the slack run command) will not work when you deploy your app in production (with the slack deploy command). You'll need to create any triggers again with the CLI.

Create the trigger file

To create a webhook trigger with the CLI, you'll need to create a trigger file. The trigger file contains the payload you used to define your trigger.

Create a TypeScript trigger file within your app's folder with the following form:

import { Trigger } from "deno-slack-api/types.ts";
import { ExampleWorkflow } from "../workflows/example_workflow.ts";
import { TriggerTypes } from "deno-slack-api/mod.ts";

const trigger: Trigger<typeof ExampleWorkflow.definition> = {
  // your TypeScript payload
};

export default trigger;

Your TypeScript payload consists of the parameters needed for your own use case. The following is a TypeScript payload for creating a webhook trigger:

import { Trigger } from "deno-slack-api/types.ts";
import { ExampleWorkflow } from "../workflows/example_workflow.ts";
import { TriggerTypes } from "deno-slack-api/mod.ts";

const trigger: Trigger<typeof ExampleWorkflow.definition> = {
  type: TriggerTypes.Webhook,
  name: "sends 'how cool is that' to my fav channel",
  description: "runs the example workflow",
  // "myWorkflow" must be a valid callback_id of a workflow
  workflow: "#/workflows/myWorkflow",
  inputs: {
    stringToReverse: {
      value: "how cool is that",
    },
    channel: {
      value: "{{data.channel}}",
    },
  },
};

export default trigger;

Use the trigger create command

Once you have created a trigger file, use the following command to create the webhook trigger:

slack trigger create --trigger-def "path/to/trigger.ts"

If you have not used slack triggers create to create a trigger prior to running slack run, you will receive a prompt in the CLI to do so.

Your app needs to have the triggers:write scope to use a trigger at runtime. Include the scope within your app's manifest.

The logic of a runtime trigger lies within a function's TypeScript code. Within your functions folder, you'll have the functions that are the steps making up your workflow. Within this folder is where you can create a trigger within the relevant <function>.ts file.

When you create a runtime trigger, you can leverage inputs acquired from functions within the workflow. Provide the workflow definition to get additional typing for the workflow and inputs fields.

Create a webhook trigger at runtime using the client.workflows.triggers.create method within the relevant function file.

const triggerResponse = await client.workflows.triggers.create<typeof ExampleWorkflow.definition>({
  // your TypeScript payload
);

Your TypeScript payload consists of the parameters needed for your own use case. Below is a function file with an example TypeScript payload for a webhook trigger.

// functions/example_function.ts
import { DefineFunction, Schema, SlackFunction } from "deno-slack-sdk/mod.ts";
import { ExampleWorkflow } from "../workflows/example_workflow.ts";
import { TriggerTypes } from "deno-slack-api/mod.ts";

export const ExampleFunctionDefinition = DefineFunction({
  callback_id: "example_function_def",
  title: "Example function",
  source_file: "functions/example_function.ts",
});

export default SlackFunction(
  ExampleFunctionDefinition,
  ({ inputs, client }) => {

  const triggerResponse = await client.workflows.triggers.create<typeof ExampleWorkflow.definition>({
    type: TriggerTypes.Webhook,
    name: "sends 'how cool is that' to my fav channel",
    description: "runs the example workflow",
    workflow: `#/workflows/${ExampleWorkflow.definition.callback_id}`,
    inputs: {
      stringToReverse: {
        value: "how cool is that",
      },
      channel: {
        value: "{{data.channel}}",
      },
    }
  });

  // ...

Webhook trigger parameters

Field Description Required?
type The type of trigger: TriggerTypes.Webhook Yes
name The name of the trigger Yes
workflow Path to workflow that the trigger initiates Yes
description The description of the trigger No
inputs The inputs provided to the workflow No
webhook Contains filter, if desired No
webhook.filter See trigger filters No

Webhook triggers are not interactive. Use a link trigger to take advantage of interactivity.

Webhook trigger response

The response will have a property called ok. If true, then the trigger was created, and the trigger property will be populated.

Your response will include a trigger.id; be sure to store it! You use that to update or delete the trigger if need be. See trigger management.


Invoke the trigger

Send a POST request to invoke the trigger. Within that POST request you can send values for specific inputs.

All JSON objects sent in the POST request need to be flat. Nested JSON objects will return a parameter_validation_failed error.

Good flattened JSON object:

{"channel":"C123ABC456","user":"U123ABC456"}

No good, very bad nested JSON object:

// JSON does not support comments but we really don't want you using this code
{"channel":"C123ABC456","user":{"first_name":"Jesse","last_name":"Slacksalot"}}

Now let's look at an entire example.

Example POST request

curl \
  -X POST "https://hooks.slack.com/triggers/T123ABC456/.../..." \
  --header "Content-Type: application/json; charset=utf-8" \
  --data '{"channel":"C123ABC456"}'

If the webhook was received and successfully handled, you'll get the following response:

{
  "ok":true
}

Onward

➑️ With your trigger created, you can now test your app by running your app locally.

✨ Once your app is active, see trigger management for info on managing your triggers in your workspace.


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