Writing A Simple Slack Bot With Node slack-client

Last week, we held our first CareEvolution hackathon of 2015. The turn out was impressive and a wide variety of projects were undertaken, including 3D printed cups, Azure-based machine learning experiments, and Apple WatchKit prototypes. For my first hackathon project of the year, I decided to tinker with writing a bot for Slack. There are many ways to integrate custom functionality into Slack including an extensive API. I decided on writing a bot and working with the associated API because there was an existing NodeJS1 client wrapper, slack-client2. Using this client wrapper meant I could get straight to the functionality of my bot rather than getting intimate with the API and JSON payloads.

I ended up writing two bots. The first implemented the concept of @here that we had liked in HipChat and missed when we transitioned to Slack (they have @channel, but that includes offline people). The second implemented a way of querying our support server to get some basic details about our deployments without having to leave the current chat, something that I felt might be useful to our devops team. For this blog, I will concentrate on the simpler and less company-specific first bot, which I named here-bot.

The requirement for here-bot is simple:

When a message is sent to @here in a channel, notify only online members of the channel, excluding bots and the sender

In an ideal situation, this could be implemented like @channel and give users the ability to control how they get notified, but I could not identify an easy way to achieve that inside or outside of a bot (I raised a support request to get it added as a Slack feature). Instead, I felt there were two options:

  1. Tag users in a message back to the channel from here-bot
  2. Direct message the users from here-bot with links back to the channel

I decided on the first option as it was a little simpler.

To begin, I installed the client wrapper using npm:

The slack-client package provides a simple wrapper to the Slack API, making it easy to make a connection and get set up for handling messages. I used their sample code to guide me as I created the basic skeleton of here-bot.

This code defines a connection to Slack using the token that is assigned to our bot by the bot integration setup on Slack's website. It then sets up a handler for the open event, where the groups and channels to which the bot belongs are output to the console. In Slack, I could see the bot reported as being online while the code executed and offline once I stopped execution. As bots go, it was not particularly impressive, but it was amazing how easy it was to get the bot online. The slack-client package made it easy to create a connection and iterate the bot's channels and groups, including querying whether the groups were open or archived.

For the next step, I needed to determine when my bot was messaged. It turns out that when a bot is the member of a channel (including direct message), it gets notified on each message entered in that channel. In our client code, we can get these messages using the message event.

Using the slack-client's useful helper methods, I turned the message channel and user identifiers into channel and user objects. Then, if the message is a message (it turns out there are other types such as edits and deletions), I send the details of the message to the console.

With my bot now listening to messages, I wanted to determine if a message was written at the bot and should therefore alert the channel users. It turns out that when a message references a user, it actually embeds the user identifier in place of the displayed @here text. For example, a message that appears in the Slack message window as:

Is sent to the message event as something like3:

It turns out that this special code is how a link to a user or channel is embedded into a message. So, armed with this knowledge and knowing that I would want to mention users, I wrote a couple of helper methods: the first to generate a user mention embed code from a user identifier, the second to determine if a message was targeted at a specific user (i.e. that it began with a reference to that user).

Using these helpers and the useful slack.self property, I could then update the message handler to only log messages that were sent directly to here-bot.

The final stage of the bot was to determine who was present in the channel and craft a message back to that channel mentioning those online users. This turned out to be a little trickier than I had anticipated. The channel object in slack-client provides an array of user identifiers for its members; channel.members. This array contains all users present in that channel, whether online or offline, bot or human. To determine details about each user, I would need the user object. However, the details for each Slack user are provided by the slack.users property. I needed to join the channel member identifiers with the Slack user details to get a collection of users for the channel. Through a little investigative debugging4, I learned that slack.users was not an array of user objects, but instead an object where each property name is a user identifier. At this point, I wrote a method to get the online human users for a channel.

Finally, I crafted a message and wrote that message to the channel. In this update of my message event handler, I have trimmed the bot's mention from the start of the message before creating an array of user mentions, excluding the user that sent the message. The last step calls channel.send to output a message in the channel that mentions all the online users for that channel and repeats the original message text.

Conclusion

Example

My @here bot is shown below in its entirety for those that are interested. It was incredibly easy to write thanks to the slack-client package, which left me with hackathon time to spare for a more complex bot. I will definitely be using slack-client again.

 


  1. or ioJS, if you would prefer 

  2. I find hackathons to be a bit like making a giant pile of sticks in the middle of a desert; it's an opportunity to get creative and build something where there seems to be nothing…using sticks…or in my case, a Node package and Slack 

  3. I totally made up the user identifier for this example 

  4. I used WebStorm 9 from JetBrains to debug my Node code, a surprisingly easy and pleasant experience 

Some of my favourite tools

Update: This post has been updated to recognise that CodeLineage is now maintained by Hippo Camp Software and not Red Gate Software as was originally stated.

If you know me, you might well suspect this post is about some of the idiots I know, but it is not, this is entirely about some of the tools I use in day-to-day development. This is by no means an exhaustive list, nor is it presented in any particular order. However, assuming you are even a little bit like me as a developer, you will see a whole bunch of things you already use, but hopefully there is at least one item that is new to you. If you do find something new and useful here, or you have some suggestions of your own, please feel free to post a comment.

OzCode

OzCode is an add-in for Visual Studio that provides some debugging super powers like collection searching, adding computed properties to objects, pinning properties so that you don't have to go hunting in the object tree, simpler tracepoint creation, and a bunch more. I first tried this during beta and was quickly sold on its value. Give the 30-day trial a chance and see if it works for you.

Resharper

This seems to be a staple for most C# developers. I was a late-comer to using this tool and I am not sure I like it for the same reasons as everyone else. I actually love Resharper for its test runner, which is a more performant alternative to Visual Studio's built-in Test Explorer, and the ability to quickly change file names to match the type they contain. However, it has a lot of features, so while this is not free, give the trial a chance and see if it fits.

Web Essentials

Another staple for many Visual Studio developers, Web Essentials provides lots of support for web-related development including enhanced support for JavaScript, CSS, CoffeeScript, LESS, SASS, MarkDown, and much more. If you do any kind of web development, this is essential1.

LinqPad

I was late to the LinqPad party, but gave it a shot during Ann Arbor Give Camp 2013 and within my first hour or two of using it, dropped some cash on the premium version (it is very inexpensive for what you get). Since then, whether it is hacking code or hacking databases, I have been using LinqPad as my standard tool for hacking.

For code, it does not have the overhead of creating projects and command line, WinForms or WPF wrapper tools that you would have to do in Visual Studio. For databases, LinqPad gives you the freedom to use SQL, C#, F# or VB for querying and manipulating your database as well as support for many different data sources beyound just SQL Server, providing an excellent alternative to SQL Management Studio.

LinqPad is free, but you get some cool features if you go premium, and considering the sub-$100 price, it is totally worth it.

JustDecompile

When Red Gate stopped providing Reflector for free, JetBrains and Telerik stepped up with their own free decompilers for poking around inside .NET code. These are often invaluable when tracking down obscure bugs or wanting to learn more about the code that is running when you did not write it. While JetBrains' dotPeek is useful, I have found that JustDecompile from Telerik has a better feature set (including showing MSIL, which I could not find in dotPeek).

Chutzpah

Chutzpah is a test runner for JavaScript unit tests and is available as a Nuget package. It supports tests written for Jasmine, Mocha, and QUnit, as well as a variety of languages including CoffeeScript and TypeScript. There are also two Visual Studio extensions to provide Test Explorer integration and a handy context menu. I find the context menu most useful out of these.

Chutzpah is a great option when you cannot leverage a NodeJS-based tool-chain like Grunt or Gulp, or some other non-Visual Studio build process.

CodeLineage

CodeLineage is a free Visual Studio extension from Hippo Camp Software2. Regardless of your source control provider, CodeLineage provides you with a simple interface for comparing different points in the history of a given file. The simple interface makes it easy to select which versions to compare. I do not use this tool often, but when I need it, it is fantastic.

FileNesting

This Visual Studio extension from the developer of Web Essentials makes nesting files under one another a breeze. You can set up automated nesting rules or perform nesting manually.

I like to keep types separated by file when developing in C#. Files are cheap and it helps discovery when navigating code. However, this sometimes means using partial classes to keep nested types separate, so to keep my solution explorer tidy, I edit the project files and nest source code files. I also find this useful for Angular directives, allowing me to apply the familiar pattern  of organizing code-behind under presentation by nesting JavaScript files under the template HTML.

Whether you have your own nesting guidelines or want to ensure generated code is nested under its corresponding definition (such as JavaScript generated from CoffeeScript), this extension is brilliant.

Switch Startup Project

Ever hit F5 to debug only to find out you tried to start a non-executable project and have to hunt for the right project in the Solution Explorer? This used to happen to me a lot, but not since this handy extension, which adds a drop down to the toolbar where I can select the project I want to be my startup project. A valuable time saver.

MultiEditing

Multi-line editing has been a valuable improvement in recent releases of Visual Studio, but it has a limitation in that you can only edit contiguous lines at the same column location. Sometimes, you want to edit multiple lines in a variety of locations and with this handy extension, you can. Just hold ALT and click the locations you want to multi-edit, then type away.

Productivity Power Tools

Productivity Power Tools for Visual Studio have been a staple extension since at least Visual Studio 2008. Often the test bed of features that eventually appear as first class citizens in the Visual Studio suite, Productivity Power Tools enhances the overall Visual Studio experience.

The current version for Visual Studio 2013 provides support for colour printing, custom document tabs, copying as HTML, error visualization in the Solution Explorer, time stamps in the debug output margin, double-click to maximize and dock windows, and much more. This is a must-have for any Visual Studio user.


  1. yes, I went there 

  2. though it was maintained by Red Gate when I first started using it