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Kotlin clean code and best practices

Clean Code Rules

Our main aim is to have a clean code, avoid common silly mistakes and reduce the load on engineers during PR reviews. This is a team effort and If anyone has something that’s generally applicable, let’s talk and decide whether it should be baked into our style guide— so everyone can benefit from it

The bad code creates a lot of distractions. It causes developers to waste time and energy navigating through functions, classes, and files, and pouring over code trying to understand it.

Working on a project where developers care about clean code makes it easy to understand its virtues; the developer can read the code from top to bottom in one go and clearly understand what it does. It makes code manageable and maintainable in the long term, isolating changes and increasing the efficiency of the team.

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File Magic Numbers

Magic numbers are the first bits of a file which uniquely identify the type of file. This makes programming easier because complicated file structures need not be searched in order to identify the file type.

For example, a jpeg file starts with ffd8 ffe0 0010 4a46 4946 0001 0101 0047 ......JFIF.....G ffd8 shows that it's a JPEG file, and ffe0 identify a JFIF type structure. There is an ascii encoding of "JFIF" which comes after a length code, but that is not necessary in order to identify the file. The first 4 bytes do that uniquely.

This gives an ongoing list of file-type magic numbers.

Image Files

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Pure ESM package

The package that linked you here is now pure ESM. It cannot be require()'d from CommonJS.

This means you have the following choices:

1. Use ESM yourself. (preferred)
   Use import foo from 'foo' instead of const foo = require('foo') to import the package. You also need to put "type": "module" in your package.json and more. Follow the below guide.
2. If the package is used in an async context, you could use await import(…) from CommonJS instead of require(…).
3. Stay on the existing version of the package until you can move to ESM.

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Code is clean if it can be understood easily – by everyone on the team. Clean code can be read and enhanced by a developer other than its original author. With understandability comes readability, changeability, extensibility and maintainability.

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General rules

1. Follow standard conventions.
2. Keep it simple stupid. Simpler is always better. Reduce complexity as much as possible.
3. Boy scout rule. Leave the campground cleaner than you found it.
4. Always find root cause. Always look for the root cause of a problem.

Design rules

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The experience of using Node.JS with TypeScript, ts-node, and ESM is horrible.

There are countless guides of how to integrate them, but none of them seem to work.

Here's what worked for me.

Just add the following files and run npm run dev. You'll be good to go!

package.json

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openssl genrsa -out CAroot.key 2048
openssl req -new -key CAroot.key -out CAroot.csr # CN should be different from the certificates below
openssl req -x509 -days 1825 -key CAroot.key -in CAroot.csr -out CAroot.crt
cat CAroot.crt CAroot.key > CAroot.pem

openssl genrsa -out mongod.key 2048
openssl req -new -key mongod.key -out mongod.csr
openssl x509 -req -days 1825 -in mongod.csr -CA CAroot.pem -CAkey CAroot.key -CAcreateserial -out mongod.crt
cat mongod.crt mongod.key > mongod.pem

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Visual Regression Testing with Jest

This is a walkthrough of how to set up Visual Regression Testing with Jest for an application created with create-react-app.

The following walkthrough uses React as an example, but the approach should work for any modern frontend library! I assume it can be used with Angular, Vue, Cycle.js and more.

This gist walks you through a create-react-app application as an example of how to set up Visual Regression Testing in Jest using libraries I wrote recently which enable this: jsdom-screenshot, jest-transform-css and jest-transform-file.

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# create assets folder in the current project
$ mkdir android/app/src/main/assets

# create bundle script
$ react-native bundle --platform android --dev false --entry-file index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res/

# execute command to run android to create debug apk
$ react-native run-android

# Or change to android folder

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cors.py for mitmproxy

Hacking CORS restriction to enable in-browser XHR to any server.

Usage

Say you are running an web app at localhost, and you want to send XHR to http://remote-server:80, but the CORS restriction forbids access because you are sending requests from an origin that remote-server:80 does not allow.

Run:

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@startuml
' uncomment the line below if you're using computer with a retina display
' skinparam dpi 300
!define Table(name,desc) class name as "desc" << (T,#FFAAAA) >>
' we use bold for primary key
' green color for unique
' and underscore for not_null
!define primary_key(x) <b>x</b>
!define unique(x) <color:green>x</color>
!define not_null(x) <u>x</u>