2018 Jul 6

> slack-rtm

After learning slack had removed support for irc gateways, I wanted to see what their alternative was for an api. I knew about some of the web API because I've messed around with hubots for various slack orgs I've been in, but I took a nice dive into the docs with the idea that I wanted to send myself a message via curl. I ended up using just a little more (needed something that spoke "websocket"), and here's my little writeup for what was required.


First thing was figuring out the high-level route, and after some reading of slack api doc pages, I determined that I'd need

  1. a slack app, with an auth key that has the proper permissions or oauth scopes (in this case "client")
  2. curl the rtm.connect REST endpoint to get a websocket connection
  3. use awebsocket client to send a json formatted message event via the rtm api

With websockets, REST, and oauth roles, it's very 5-years-ago's next-gen webâ„¢ (and I'm really not sure what today's next-gen web is, but I imagine it's http 2.0 functional monito blockchains).


Here's what I did to get a token with the correct permissions (it was not obvious, and I wonder if slack will disallow this at some point):

  1. create a [new app] if you haven't already
  2. go to app control panel and open the "Add features and functionality" dropdown and select "Permissions"
  3. right-click on Reinstall App button underneath the access token and copy the link location. It should look something like
  1. modify the scope url parameter to read scope=client
  1. visit that url in a browser, and accept the change in permissions; now the access token will have client scope

Now you can use the app's token to access a bunch of REST endpoints.

socket up

I made a little shell function while I was poking around the REST endpoints, you may find it useful too:

$ slackc() {
	shift 2
	curl -X $method -d "Authorization: Bearer $TOKEN" $@ "https://slack.com/api/$api"

I chose wsc as a websocket client because it was small and easy to install via npm.

$ npm install wsc
$ alias wsc=<path to node_modules>/wsc/wsc

Now, you can call

$ TOKEN=<app token, starts with "xoxp-">
$ slackc GET rtm.connect |jq . >rtm.connect.txt
$ wsc $(<rtm.connect.txt jq .url |sed 's/^"//' |sed 's/"$//')

You need to replace <app token...> with your slack app token which can be found on the app settings page in slack. Here we call the rtm.connect REST endpoint, which returns some json that has a websocket url among other things. The little shell stuff is there to extract the url via jq, and strip the quote characters with sed

Now you've got a slack rtm connection.

Talk to yourself

I joined an im with myself using the slack webclient, and got an event in wsc

< {"type":"im_open","user":"UXXXXXXXX","channel":"DXXXXXXXX","event_ts":"1527543437.000020"}

That showed me the channel id I needed DXXXXXXXX, and I sent a message to myself:

> { "id": 1, "type": "message", "channel": "DXXXXXXXX", "text": "testing this websocket" }

and it showed up in the webclient!