Custom Command Handler Example using Express.js

Custom commands and action handlers

Simple custom slash command

In this example, we implement a custom slash command that can be used to create support tickets.

Setup

Application Settings

First we set the custom_action_handler_url in the application settings:

await client.updateAppSettings({
    custom_action_handler_url: "https://example.com/{type}",
});

You can use a {type} variable substitution in the URL to pass on the name of the command that was triggered.

Create Custom Command

Next, we register a “ticket” custom command and provide a description of the command and its arguments.

await client.createCommand({
    name: "ticket",
    description: "Create customer support tickets",
    args: "[description]",
});

Create Channel Type

In order to be able to use this command in a channel, we’ll need to create a channel type that includes the ticket command.

await client.createChannelType({
    name: "support-channel-type",
    commands: ["ticket"],
});

Create Channel

We can now create a new channel that will support our using new ticket command.

const channel = client.channel("support-channel-type", "support-chat", {
    name: "Support Chat",
});
await channel.create();

When we look at the channel’s config, we should see the ticket command listed there:

console.log(channel.getConfig());
{
  name: 'support-channel',
  commands: [
    {
      app_pk: 12345,
      name: 'ticket',
      description: 'Create customer support tickets',
      args: '[description]',
    }
  ],
  ...
}

In the frontend this will make the ticket command show up in the command auto-completion popup.

Custom Command Handler

Now we’re ready to use our custom ticket command.

channel.sendMessage(text: "/ticket my laptop stopped working");

This will try to send a POST request to our custom_command_url endpoint with a JSON encoded body like:

{
  "message": {
    "id": "gmoree-2b1909be-8b96-42c5-9c5b-01f84ea23330",
    "text": "/ticket my laptop stopped working",
    "command": "ticket",
    "args": "my laptop stopped working"
    "type": "regular",
    "attachments": [],
    ...
  },
  "user": {
    "id": "gmoree",
    "role": "user",
    "name": "Guyon Moree",
    ...
  }
}

Rewrite Message

To handle this request we’ll use Express JS. We’ll start by simply rewriting the message text to return the argument that was passed onto the ticket command:

ticketCmdHandler = (req, res) => {
    // the body of the message we will modify 
    // based on user interactions
    let message = req.body.message;

    message.text = `ticket created about "${message.args}"`;

    res.setHeader('Content-Type', 'application/json')
    res.end(JSON.stringify({message}))
};

This rewrites the message text and will be reflected in the frontend.

Actions

In order to add some interactivity to our command, we’ll be using message attachment actions, to let the user confirm or cancel the support ticket request.

message.text = `creating ticket about "${message.args}"`;
message.attachments = [
   {
       type: "text",
       actions: [
           {
               type: "button",
               name: "action",
               value: "confirm",
               text: "Confirm",
               style: "primary",
           },
           {
               type: "button",
               name: "action",
               value: "cancel",
               text: "Cancel",
               style: "default",
           },
       ],
   }
];

The rewrite of the message text and attachment action will be reflected in the frontend.

Form Data

When a user interacts with one of the actions, the handler will be called again with an additional form_data attribute that will contain the chosen action:

{
 "message": {
   ...
 },
 "user": {
   ...
 },
 "form_data": {
   "action": "confirm"
 }
}

Now that we have access to the chosen action, we can act accordingly. In case of a confirmation, we will finalize the message text and remove the previously added attachments. In case of cancel, we simply set the message to null, which will remove the message completely:

const formData = req.body.form_data || {};
const action = formData["action"];

switch (action) {
   case "confirm":
       message.text = `ticket created about "${message.args}"`;
       message.attachments = null;
       break;
   case "cancel":
       message = null;
       break;
   default:
       ...
}

Message Types

The default message type is regular, which means it will be shown to everyone in the channel. It is common to set the message type to ephemeral while interacting with the command and set it to regular once the message has been finalized.

A 3rd type is error, which we can use to mark the message as invalid, eg. when command is missing a required argument.

switch (action) {
   case "confirm":
       message.type = "regular";
       message.text = `ticket created about "${message.args}"`;
       message.attachments = null;
       break;
   case "cancel":
       message = null;
       break;
   default:
       if(message.args.trim() === "") {
           message.type = "error";
           message.text = "missing ticket description";
           break;
       }
       ...

Custom Command Interaction with MML

Using the attachment actions is limited to Buttons. If we want to use more elaborate interactions, we can use MML to create a form.

Rewrite Message MML field

Previously, we modified the text field and added an attachment with action on the message to communicate with the user. Now, we will replace these by rewriting the mml field instead:

message.mml = `
   <mml name="ticket_form">
       <text>creating ticket about "${message.args}"</text>
       <row>
           <column width="2">By:</column>
           <column width="10">
               <input type="text" name="reported_by" value="${user.name}" />
           </column>
       </row>
       <button_list>
           <button name="action" value="confirm">Confirm</button>
           <button name="action" value="cancel">Cancel</button>     
       </button_list>
   </mml>
`;

This will display 2 buttons like before, and an additional text input field that will allow us to enter the name of the person that reported this ticket, with a default set to the user associated with the message.

Handling the form works similar to handling the attachment action, in fact we don’t have to change anything for those. We only need to capture the reported_by field and transform the remaining messages to mml equivalents:

switch (action) {
   case "confirm":
       const reportedBy = formData["reported_by"];
       message.type = "regular";
       message.mml = `
           <mml>
               <text>ticket created about "${message.args} by ${reportedBy}"</text>
           </mml>
       `;
       message.attachments = null;
       break;

Standalone MML Messages & Interactions

Messages containing MML are not necessarily initiated by slash commands, but can also be sent through the client’s sendMessage api.

channel.sendMessage({
   mml: `<mml name="mml_form">
           <text>This is a standalone mml message</text>
           <button name="action" value="ok" text="ok"/>
         </mml>`,
   user: {
       id: "bot",
       name: "Mr. Bot",
       image: "bender.jpg"
   }
});

When a user interacts with the message, the custom command handler endpoint will be called, with the command name set to mml.

Additionally, the form data will include a field containing the mml name attribute value, called mml_name, that can be used to identify the form that initiated the request.