slack-weatherbot

A Node.js-based service that responds to the custom Slack command /forecast <zipcode>. Slack-weatherbot looks up the forecast info by zip code, utilizing the developer API provied by Weather Underground.

Overview

I implemented this using the Node.js and the Express application framework. This project relies on the following modules which can be installed via npm.

• express
• url
• body-parser
• request

Usage

To use, Slack must issue the 'slash' command /forecast <zipcode> as a POST to the slack-weatherbot service. The service will return a payload of the following form

 {
  "response_type": "in_channel",
    "attachments": [
      {
        "text": "Location: "<provided zipcode || default>",
        "image_url": "<forecast_image_url>"
      }
    ]
  }

If no zip code is provided, the service defaults to zip code 78751 (Austin, TX). The input is validated and any non-5-digit inputs are rejected with an error message to the issuer. If the zip code does not exist in the U.S., a different error message will notify the user.

The slack-weatherbot returns two forecasts, one for the day, and one for the next night. To do this, I used the multiple responses capability of Slack via the POST callback_url provided in the original request. (This is as opposed to the inline result you can provide directly via the response which only supports 1 message.)

Installation

Running the slack-weatherbot service is as simple as executing node weatherman.js. However, in order to get it up and running behind an internet-routable DNS name, I added a DNS CNAME to map slackcommands.tpetz.com to my existing DNS entry for tpetz.com. This is because I have several different webservers running on my single Linode server and I wanted this to be served in it's own VirtualHost. The following apache2 configuration creates a proxy that passes all requests to slackcommands.tpetz.com onto my node server running on localhost:3338.

<VirtualHost *:80>
    ServerName slackcommands.tpetz.com
    ServerAlias slackcommands.tpetz.com
    ServerAdmin webmaster@localhost
 
    ProxyPass / http://127.0.0.1:3338/
    ProxyPassReverse / http://127.0.0.1:3338/
    ProxyRequests Off 
    ProxyPreserveHost On
</VirtualHost>

This installation allowed me to configure the slash command using URL: http://slackcommands.tpetz.com/forecast for the POST.

Configuration

The Weather Underground API requires an WEATHER_API_KEY which is provided as a hardcoded string in the code. Normally the service would also check the incoming Slack TOKEN to protect against unauthorized use, but I am not currently checking the Token in case anyone wants to test against my running slack-weatherbot by configuring their own "/forecast" slash command.

To test the service, configure Slack to send a 5 digit zip code to http://slackcommands.tpetz.com/forecast via a custom Slash command.

Known Issues

• The WEATHER_API_KEY is hardcoded in the source code which is a security concern, it would be better to provide it via an ENV variable but this would complicate testing somewhat so I've left it in for now.
• The service only supports U.S. zip codes, a future version could easily support city-based lookups using a different WeatherUnderground API for the back-end call.

References

The following were especially helpful resources:

• https://api.slack.com/slash-commands
• https://www.wunderground.com/weather/api/d/docs?d=index&MR=1
• https://mager.co/how-to-write-a-slackbot-in-40-lines-of-code-52cf0c4fcf42
• http://www.girliemac.com/blog/2016/10/24/slack-command-bot-nodejs/