How to work with a private library in ClojureScript

Dashman is composed of many components  including three desktop apps written in ClojureScript using Electron that share code through a private library (as in, it’s not open source).

To have continuous integration and a set up that is easy to boostrap, that library should be deployed to a private repository. I achieved that using the plug in s3-wagon-private so that the project.clj of the common library looks like this:

:repositories [["private" {:url           "s3p://s3-bucket-for-my-project/releases/"
                           :username      "not-telling-you"
                           :passphrase    "not-telling-you-either"
                           :sign-releases false}]]

:plugins [;...
          [s3-wagon-private "1.3.0"]]

You should never have production or even staging credentials on your source code repository; but those credentials are neither. They allow to compile the project so, pretty much everybody that has access to the source code also needs access to that private repository. Having them in project.clj simplifies CI, on-boarding developers, etc.

One you have that you can deploy the library by executing:

lein deploy private

The project of the apps using the common library look similar:

:repositories [["private" {:url           "s3p://s3-bucket-for-my-project/releases/"
                           :username      "not-telling-you"
                           :passphrase    "not-telling-you-either"
                           :sign-releases false}]]
:dependencies [;...
               [tech.dashman/clientcommon "0.1.0-SNAPSHOT"]]

:plugins [;...
          [s3-wagon-private "1.3.0"]]

Yes… very similar.

The next issue is compiling and re-loading code. You could modify the common library, install it, re-compile the apps, and re-run the apps. And you could do it while wearing a mullet and watching MacGyver (the original one). This is not the 80s! You want code reloading and all the goodies.

If you are using Clojure, you should look into checkouts and maybe lein-checkout. In ClojureScript you can just add the path of the source code to your project even if it’s outside the project, with one gotcha. You might be used to a config like this:

:cljsbuild {:builds {:app {:source-paths ["src/app"]}}}

which would imply this might work:

:cljsbuild {:builds {:app {:source-paths ["src/app" "../clientcommon/src"]}}}

It might on non-Windows platforms, on Windows it doesn’t. On Windows you want this:

:cljsbuild {:builds {:app {:source-paths ["src/app" "..\\clientcommon\\src"]}}}

Since you should probably never commit that anyway, it’s not a big deal.

ClojureScript debouncer

I’m developing Dashman in ClojureScript (and Clojure) and as I was developing the cookie handler I found sites that constantly modify the cookies. As in, many times per second. Obviously I don’t want to encrypt the cookies and send them to the server that often, but even without taking that into account, just storing them to keep track of them in an atom, as in:

(reset! cookies new-cookies)

was slowing down the app considerably. I found myself needing to debounce so many calls as there’s no value in the middle calls, only the last one. Let’s backtrack a little bit here.

The term to debounce comes from electronics:

To remove the small ripple of current that forms when a mechanical switch is pushed in an electrical circuit and makes a series of short contacts.

In programming it refers to a signal that gets emitted often and you want to process it but you don’t care about processing every intermediate value. To tie into electronics imagine you have a program that receives a message every time the temperature changes and the message contains all the temperature changes for the day. Clearly each message doesn’t have to be processed, only one, only the latest.

Here’s where a software debouncer can help. It’s a function that gets a function and returns another function. When you call the resulting function 10 times, it will only call the original function once, with the last value it received.

I found this debouncer written by David Nolan: and in the comments you can start to see that writing a debouncer might not be a trivial as you may think. One of the comments point to this other version: The comment implies this is a more correct version but I haven’t verified it myself. In that last page you can see someone found a bug and posted an improved version.

For me, when a supposedly simple code snippet generates so many comments and versions, it’s better to find a library that implements it than to copy and paste and never maintain it again. Unfortunately, I couldn’t find a ClojureScript debouncer library but I got pointed to goog.function.debounce which you can use this way;

(ns whatever
  (:require [goog.functions]))

(def debounced-println (goog.functions.debounce println))

The Highlander query with Rails’ ActiveRecord

For those cases in which there can be one and only one record on the database with certain fields and I don’t just want to get the first one and silently get the wrong one. I want to make sure there’s one and only one, so, I wrote this little extension to ActiveRecord that does exactly that:

module ActiveRecordExtension
  extend ActiveSupport::Concern

  class_methods do
    def one_and_only
      records = limit(2).all.to_a
      if records.count > 1
        raise "#{self} generated more than one record when expecting only one."

    def one_and_only!
      one_and_only.tap do |record|
        if record.nil?
          raise "#{self} didn't generate any records."

ActiveRecord::Base.send(:include, ActiveRecordExtension)

The first method, one_and_only, will raise an exception if there’s more than one item but it’ll return null if there aren’t any. one_and_only! will fail if there isn’t exactly one and only one record in the database.

If you don’t know why I’m calling this The Highlander query, you should go and watch Christopher Lambert’s masterpiece.

Screensaver Ninja might be coming back

Since discontinuing Screensaver Ninja, I have received many messages asking when it is coming back: over Twitter, Facebook, email, and even one person tracking me down on Reddit..

For those of you who don’t know what Screensaver Ninja is, here is the old explainer video:

It has been very painful to read these messages for a couple of reasons. Firstly, I strongly believe in the product. I want to have it; use it; and enable others to use it. I constantly see expensive and badly designed dashboards or wasted screens, which my product will address. Secondly, judging by the requests, other people want this just as much as I do. Not proceeding with Screensaver ninja could be a wasted business opportunity; although it is hard to tell if the demand is enough to support its development right now.

I set up a landing page explaining what happened to Screensaver Ninja and a form for people to register for notifications of its potential comeback. This was a way to save everybody’s time and frustration; for those emailing requests for up to date information when I could only say, with sadness, “it’s over”. To my surprise, this form has been gathering five or so leads a week, which is rather a lot for an abandoned product.

I have started playing with the idea that I might revive Ninja: This time I have designed a bigger system that covers many more use cases and allows me to support both Windows and Mac OS as well as other platforms just as easily.

During this process I identified the technological bottlenecks; the aspects to product creation that can take months to negotiate and solve, such as hacking Apple’s cookie jar or packaging Chromium. In doing so, I have built a selection of prototypes testing my choices – and everything is working beautifully.

So that’s it: I have decided to revive Screensaver Ninja. I have emailed all of you whom have shown interest to tell you the good news, and have received an overwhelmingly positive response from both individuals and corporations; some wanting to run hundreds of instances.

I want to be completely transparent with my supporters; I am building Screensaver Ninja by myself in my spare time between long days and after hours work at two different consultant gigs. Whilst I am looking into the options of partnerships, developers, and marketers, I have decided not to wait for these additions to the team in order to make progress. I’m very excited about this phase both from the technical as well as the business points of view so Screensaver Ninja is moving forward and I will have frequent updates.

Going into the property business 

I’m a tech entrepreneur and that has not changed, but after six or seven years of trying to have at least moderate success, I’m starting to hedge my bets.

On the side, I want to have some passive income and it looks to me like buy and hold properties, that is, buying them and renting them out, also known as buy to let, is the way to move forward. I identified some very profitable areas and they are in the least expected places. For example, in London you can expect a return on investment of around 3% while I’m getting something around 16%.

If you want to listen to my journey, I’m documenting it as I go with Clayton Morris on his podcast about investing in property. He just published the second episode in which I talk about getting the money for my first two deals.  I just pulled the trigger on starting the business. I’m super excited and I can’t wait to share more good news in the next episode. 

Emacs is hurting Clojure 

Emacs is a very powerful text editor and its popularity amongst Clojurians is easily understood. Emacs has a long tradition in the Lisp communities as it’s written, in a big part, in a flavor of Lisp called Emacs Lisp.

Because of its history, it handles Lisp code wonderfully, with automatic correct indentation, paraedit, integration with REPLs, etc. But Emacs is really hard to use.

Yeah, most Clojurians know how to use it by now and they suffer from bias: “it’s not that hard” they say. Learning Emacs or Clojure is hard enough. Combining them is insane.

Many Clojurians also say it’s worth it. And again, I think they are biased. Human brains are very good at forgetting pain. Other editors these days are also very powerful and although not as much as Emacs, their usage is intuitive so you can achieve a higher level of proficiency just by using it, without spending time and effort in becoming better at it.

The way Emacs is hurting Clojure is by Clojurians maintaining this myth that you need to use Emacs for Clojure. This is not done by simple statements but by a general culture of jokes saying things such as “you are wrong if you don’t use emacs”.

Me, personally, I don’t care what editor you use. If you want to learn Emacs, go for it. Intellij and Cursive is much easier to use and almost as powerful. When I compare myself to another clojurian, productivity is generally decided by knowledge of the language and libraries, not the editor. If you want to use another editor, so be it. It’s better if they understand Lisp code but it’s not a deal breaker for learning Clojure.

I do care about the success and popularity of Clojure. Coupling the growth of the language to the use of an editor that is hard to use and non intuitive makes no sense. It’s hurting us. Even if you are an Emacs power user, when you talk to a Clojure newbie, please, don’t push it down their throats.

Thank you.

Avoiding threads of emails when developing a Rails application

Call to Buzz, like many applications I developed before, sends emails. Lot’s of emails. To avoid accidentally emailing a customer or random person I use mail_safe. It’s one of the first gems I install on a Rails project and you should too. mail_safe re-writes the to-header so you end up receiving all the emails that you sent.

Once you are receiving all these emails, there’s another problem. They are likely to have exactly the same subject, so, mail clients are likely to group them in threads, which can be annoying. To avoid that, I added this to my ApplicationMailer class and voila! all emails have a unique subject:

if Rails.env.development?
  after_action :uniq_subjects_in_development

  def uniq_subjects_in_development
    mail.subject += " #{SecureRandom.uuid}"