Slack chat.postMessage with attachments

SlackPostMessageWithAttachments.js

var http = require("https");
var querystring = require('querystring');

//2 attachments as JavaScript Objects
var attachments = [{
    fallback: "Attachment 1 Fallback",
    title: "This is Attachment 1",
    text: "Attachment 1 Text",
    color: "#3964db"
}, {
    fallback: "Attachment 2 Fallback",
    title: "This is Attachment 2",
    text: "Attachment 2 Text",
    color: "#3964db"
}];

//add the attachments to the message by stringify-ing them
//posting without stringify-ing the attachments will lead to an error from the Slack API
var message = {
    token: "your-token",
    channel: "@daniel",
    as_user: false,
    username: "daniel",
    attachments: JSON.stringify(attachments),
    text: "This is a message with attachments"
}

var qs = querystring.stringify(message);

var options = {
    "method": "GET",
    "hostname": "slack.com",
    "path": "/api/chat.postMessage?" + qs
};

var req = http.request(options, function (res) {
    var chunks = [];

    res.on("data", function (chunk) {
        chunks.push(chunk);
    });

    res.on("end", function () {
        var body = Buffer.concat(chunks);
        console.log(body.toString());
    });
});

In the API documentation for chat.postMessage, the example shows you can add attachments to the message. Despite the endpoint name chat.postMessage the API call is actually an HTTP GET, with the message object passed as part of the URL query string.

Since the attachments are an array, the brackets can confuse the Slack API and lead to the cryptic invalid_array_arg error. The solution to this is to stringify and url encode the attachment array before adding it to the query string. I couldn't find reference to this anywhere in the API documentation, so I'm hoping this gist will help someone else.

Thank you, I needed this!

+1 Thanks!

+1 Thanks!

👍 Awesome! Thanks! 💃

🙌 tks a lot

Nice. 👍

First result in Google about the Slack invalid_array_arg error. Thanks a lot 😊

method should be POST now
https://api.slack.com/methods/chat.postMessage

This is still true even though the endpoint is POST now, so so bad

https://api.slack.com/methods/chat.postMessage#arg_attachments

A JSON-based array of structured attachments, presented as a URL-encoded string

So it's not JSON, it's JSON-based