Comparison of Golang Input Validator Libraries

This is a comparison of some open source golang validation libraries on github. These libraries do not handle data sanitization. Each libraries will have it's strengths and weakness. Let's get started.


go-playground/validator implements value validations for structs and individual fields based on tags. It's probably the oldest and most popular validation library out there. It supports complex validation methods such as cross-field comparison, i18n, diving into fields. This library would be great if you have complex validation requirements.


asaskevich/govalidator is a package of validators and sanitizers for strings, structs and collections, and is based on validator.js. Similar to go-playground/validator, govalidator uses struct tags to define rules. It also provides individual validation functions and is a little easier to learn. This is a great alternative if you like mature and popular libraries.


go-ozzo/ozzo-validation provides configurable and extensible data validation capabilities. Unlike the previous two libraries, ozzo-validation uses programming constructs instead of struct tags to define rules. This makes it less error-prone and more readable than the other two.


AgentCosmic/xvalid is a lightweight validation library that can export rules as JSON so browsers can apply the same rules. xvalid is similar to ozzo-validation in that it uses programming constructs instead of struct tags to define rules. Being able to export rules to the browser will help you keep validation rules consistent. This is a great library if you only need simple validation.

Keywords: golang, library, validator, validation, open source, comparison, alternative

Increase Golang web app testing speed by over 2 times with parallel testing and more

We're all familiar with how tests get slower as we add more over time. If you're not already using parallel testing in Go, this article will give you an example of how to implement it in a web application. In one of my projects, I managed to decrease test time from 40s to just over 10s by employing these techniques.

The Solution

The easiest way to get major speed improvements is to add t.Parallel() to every top level test function.

func TestMyFunc(t *testing.T) { t.Parallel() // add this line ... testing code }

There's a pretty high chance that your test might break. The biggest culprit is having have singletons in your code. If any test uses a shared state, whether in a singleton or not, you cannot make that particular test parallel. Other tests can still be parallel. Some other obstacles could be caused by bad testing practice such as relying on previous test states for the next test, or using the same rows in a table etc. You can solve this by ensuring each test are designed to run in isolation.

Other Techniques

Another simple way to decrease test run time is simply not cleaning up the tests every run. That means not deleting from the database etc. If your tests are designed in isolation, this will be an easy change. The other benefit from this technique is having your tests run in a "dirty" state that mimics production environments.

You can take it a step further and break tests in smaller units like so:

func TestMyFunc(t *testing.T) { t.Run("t1", func (t *testing.T) { t.Parallel() }) t.Run("t2", func (t *testing.T) { t.Parallel() }) }

This will also help during debugging because you can isolate the test i.e. -run TestMyFunc/t2

You can shave off a few more seconds by running your code and database off a ramdisk. See how I run Go code from ramdisk.

Lastly, if you're not already using a tool to automatically run your code when you save a file, you should start now to save plenty of time during development.

Keywords: golang, go, test, speed, performance, parellel

How to Get File Notification Working on Docker, VirtualBox, VMWare or Vagrant

Have you tried using tools like inotify, nodemon or webpack inside Docker or VirtualBox but just couldn't get it to work? The problem lies with the virtual file system. They simply do not support the file notification API. The only existing solution out there is to use a polling method. One such program is fswatch. But it becomes slow once the number of files become big.

xnotify solves all these problems easily while adding some awesome features for common use case. It works by sending file events from your host machine to your virtual machine over HTTP. It works on all popular platforms like Windows, Linux and OSX with a single binary. In addition to that, you can easily run commands on file change using the -- option.

Here's a real world example of how I automatically run my Go test and reload the server automatically within VirtualBox:

PowerShell script on my windows host: .\xnotify.exe --verbose --client :8001 -i . -e "(vendor|\.git)$"

The command above watches all files in the current directory, excluding "vendor" and ".git" folders, and sends the event to localhost:8001, the address where our next program is listening on.

Bash script on my Linux VM to automatically run tests: ./xnotify --verbose --listen "" --base /my/project/dir --batch 50 -- go test -c app/test -- ./test.test -test.failfast

This will listen on for file events that the Windows program is sending. Then it runs the commands after the -- option, using the working directory of /my/project/dir.

Bash script on my Linux VM to automatically run reload the server: ./xnotify --verbose --trigger --listen "" --base /my/project/dir --batch 50 -- go build cmd/main.go -- ./main

This works in the same way, except that the commands after -- is used to run the web server instead of the tests.

For more examples, see the README at the project page.

Keywords: file, notification, docker, virtualbox, vmware, vagrant, xnotify

Go: Automatically Run Tests or Reload Web Server on File Changes

Wouldn't it be convenient if you could automatically run your tests or reload your web server whenever you save your file. Here's a very simple way to achieve it. First download xnotify. Then run the following command in your project directory.

./xnotify -i . -- go test -c ./... -- ./test.test

That will automatically run your tests.

./xnotify -i . -- go build main.go -- ./main

That will automatically reload your web server.

What the command does is watch the current directory with -i . then runs the command that comes after --. The equivalent of running go test -c ./... && ./test.test. The -c option tell Go to compile into a binary instead of running the test. We need to do this so that the child process would not stay alive after killing the parent process. Here's a more complex use case:

./xnotify -i . -e "(vendor|\.git)$" --batch 50 -- go test -c -- ./test.test -test.failfast TestThisFunction

Some explanation on the code:

-e "(vendor|\.git)$" excludes "vendor" and ".git" directory.

--batch 50 will wait for 50ms before executing so that saving multiple files at once wouldn't restart too many times.

This time we pass a package name instead of the path with

-test.failfast will stop the test if any tests fails. TestThisFunction will only run the test function called "TestThisFunction".

Keywords: go, automatic, cli, xnotify, test, build, server

Which subreddit deletes the most comment? Is there censorship?

If you've been a long time reddit user you've probably realized that some subreddits are filled with deleted comments. Out of curiosity, I decided to do a quick analysis on just how many comments are deleted. To get started let's look at the result.


Looking at the top 10 subreddit gives us a good baseline for how many comments are usually deleted because of the larger sample size they provide. Interestingly r/science has an absurd amount of deleted comments. In the second chart we see that the average amount of deleted comments is 0.23% without r/science. That number will be useful for the next chart.

In the last chart I picked some interesting subreddits to study. The green line shows the average amount that was taken from the previous chart. Something I noticed is that style of moderating is a bigger influence on the deletion than the nature of the sub. For example we can see AskMen (0.11%) vs AskReddit (0.2%) vs AskWomen (2.53%), and relationship_advice (0.38%) vs relationships (1.32%).


All data were pulled from the top 30 posts in each subreddit over 7 days in an ad-hoc manner. All were done at least 24 hours apart to prevent any overlap.

Source Code

I'm releasing the source code so everyone can perform their own analysis. It's written in JavaScript and needs to be run in the browser on reddit. The main functions to run are right at the bottom.

function getPosts(subreddit, callback) { fetch('' + subreddit + '?&sort=hot') .then(response => { return response.json() }) .then(data => { let ids = Object.keys(data.posts) callback(ids) }) .catch(err => { console.error(err) }) } function getComments(id, callback) { fetch('' + id + '?sort=top&depth=100&limit=100000') .then(response => { return response.json() }) .then(data => { let stats = { total: 0, deleted: 0 } for (let id in data.comments) { let comment = data.comments[id] if (comment.deletedBy == 'moderator') { stats.deleted++ } } callback(stats) }) .catch(err => { console.error(err) }) } function analyze(subreddit, callback) { getPosts(subreddit, ids => { var total = 0, deleted = 0, counted = 0 for (let id of ids) { getComments(id, stats => { total += deleted += stats.deleted counted++ if (counted == ids.length) { callback(subreddit, deleted, total); } }) } }) } function analyzeToJSON(subs) { var dict = {} function loop(i) { if (i >= subs.length) { console.log(JSON.stringify(dict)); return } analyze(subs[i], (sub, deleted, total) => { dict[sub] = { deleted: deleted, total: total } loop(++i) }) } loop(0) } function analyzeToCSV(subs) { let csv = '' function loop(i) { if (i >= subs.length) { console.log(csv); return } analyze(subs[i], (sub, deleted, total) => { csv += `${sub},${deleted},${total},${Math.round(deleted / total * 10000, 2) / 100}%\n`; loop(++i) }) } csv += 'sub,deleted,total,percent\n'; loop(0) } function compile(entries) { let results = {} for (let entry of entries) { for (let sub in entry) { if (!results[sub]) { results[sub] = { deleted: 0, total: 0, } } let r = results[sub] let e = entry[sub] r.deleted += e.deleted += } } for (let sub in results) { let r = results[sub] r.percent = r.deleted / } return results } function getMean(entries) { let total = 0, count = 0 for (let sub in entries) { total += entries[sub].percent count++ } return total / count } function getMedian(entries) { let list = [] for (let sub in entries) { list.push(entries[sub].percent) } list.sort((a, b) => a - b) if (list.length % 2 === 0) { let a = list.length / 2, b = a - 1 return (list[a] + list[b]) / 2 } else { return list[(list.length - 1) / 2] } } function getStdDiv(entries) { let list = [] let mean = getMean(entries) for (let sub in entries) { let d = entries[sub].percent - mean list.push(Math.sqrt(d * d)) } return list.reduce((accumulator, currentValue) => accumulator + currentValue) / list.length } function getCSV(data) { let csv = 'sub,deleted,total,percent\n' for (let sub in data) { let r = data[sub] csv += `${sub},${r.deleted},${},${Math.round(r.percent * 10000, 2) / 100}%\n`; } return csv } function formatPercent(i) { return Math.round(i * 10000, 2) / 100 + '%' } function report(entries) { const percents = Object.values(entries).map(e => e.percent) const max = formatPercent(Math.max.apply(null, percents)) const min = formatPercent(Math.min.apply(null, percents)) console.log(`Mean: ${formatPercent(getMean(entries))}, Median: ${formatPercent(getMedian(entries))}, Standard Deviation: ${formatPercent(getStdDiv(entries))}, Min: ${min}, Max: ${max}`); console.log(getCSV(entries)); } var presets = { top10: [ 'funny', 'AskReddit', 'gaming', 'pics', 'science', 'worldnews', 'todayilearned', 'aww', 'movies', 'videos' ], custom: [ 'AskReddit', 'AskMen', 'AskWomen', 'TwoXChromosomes', 'sex', 'relationships', 'relationship_advice', 'unpopularopinion', 'news', 'politics', 'The_Donald', 'MGTOW', 'AmItheAsshole', ], } var results = { top10: [{ "funny": { "deleted": 3, "total": 5053 }, "AskReddit": { "deleted": 34, "total": 8687 }, "gaming": { "deleted": 2, "total": 3954 }, "pics": { "deleted": 4, "total": 3691 }, "science": { "deleted": 195, "total": 2786 }, "worldnews": { "deleted": 30, "total": 5580 }, "todayilearned": { "deleted": 1, "total": 4889 }, "aww": { "deleted": 5, "total": 3133 }, "movies": { "deleted": 10, "total": 5129 }, "videos": { "deleted": 1, "total": 4038 } }, // add more results here ], custom: [{ "AskReddit": { "deleted": 34, "total": 8723 }, "AskMen": { "deleted": 0, "total": 1626 }, "AskWomen": { "deleted": 37, "total": 2351 }, "TwoXChromosomes": { "deleted": 67, "total": 1872 }, "sex": { "deleted": 9, "total": 549 }, "relationships": { "deleted": 12, "total": 1276 }, "relationship_advice": { "deleted": 12, "total": 2684 }, "unpopularopinion": { "deleted": 5, "total": 2233 }, "news": { "deleted": 20, "total": 3252 }, "politics": { "deleted": 30, "total": 7723 }, "The_Donald": { "deleted": 21, "total": 3069 }, "MGTOW": { "deleted": 1, "total": 850 }, "AmItheAsshole": { "deleted": 30, "total": 8131 } }, // add more results here ], } // analyzeToJSON(presets.top10) // analyzeToCSV(presets.custom) // report(compile(results.top10)) // report(compile(results.custom))
Keywords: reddit, subreddit, comments, censorship

How to Compile Go Code 40% Faster With RAM Disk

Go is already famous for it's impressive compilation speed. But if you came from a scripting language with practically no compile time, you're probably not satisfied. Here's the compile time after running go build main.go a few times to warm up the file system.

real 0m2.590s user 0m2.685s sys 0m0.775s

It's easily 2 to 3 times slower when the files aren't cached. Which could happen if your disk is experiencing a lot of usage. Here's the compile time when compiling from RAM disk. A whopping 40% faster; almost a second off.

real 0m1.871s user 0m2.124s sys 0m0.380s

Here's the bash script to get things working:

#!/bin/sh if [ ! -d ~/ramdisk ]; then mkdir ~/ramdisk fi sudo mount -t tmpfs -o size=512M tmpfs ~/ramdisk rsync -ah ~/go ~/ramdisk/ rsync -ah --exclude '.git' ~/path/to/project ~/ramdisk export GOPATH=$HOME/ramdisk/go

This creates a directory under the home folder as ~/ramdisk. Then assigns 512MB disk space and mounts it on the RAM. The rsync calls copy all Go files and project files to the RAM disk. Finally, it sets GOPATH to the new Go path under ~/ramdisk.

The next step is to reflect all file changes to the RAM disk instead of editing the files directly on it. This way you don't have to worry about losing your work. To do that we need a tool to watch for file changes and automatically duplicate the file. You can use any tool you like e.g. inotify, fswatch, nodemon etc. I'm going to use xnotify, a high level tool which can help with the build process.

./xnotify --verbose -i . --base /home/vagrant/ramdisk/project --batch 50 -- go build cmd/main.go -- ./main | xargs -L 1 ./

#!/bin/sh NAME=$2 SRC=/path/to/project/$NAME if [ -f $SRC ]; then echo Copying: $NAME cp $SRC ~/ramdisk/project/$NAME fi

The command above basically copies the file to the RAM disk and runs go build cmd/main.go && ./main when a file changes. Now if we want to stop using the RAM disk we just need to run this script:

#!/bin/sh sudo lsof -n ~/ramdisk sudo umount ~/ramdisk rm ~/ramdisk -r export GOPATH=$HOME/go
Keywords: go, golang, compile, speed, ram, disk, ramdisk

Theory of Cost Driven Testing


In this article we shall explore guidelines that can help us reap the benefits of automated software testing with the least effort and time possible. There's always a trade off between writing bug free software and delivering results quickly. Thanks to the law of diminishing returns, we know that every additional effort produces less returns than before. This is especially true in startups and small dev teams with tight deadlines. Why are some software "bug free" despite having no automated test? Why do some software have many bugs despite high code coverage? Can we write tests that we are very likely to benefit from while not writing any test that is unlikely to help us?

Critical Features

Critical features are those that must be working correctly or there will be dire consequences. A bug in the feature could have catastrophic consequences such as losing your job, losing money, someone dying etc. This should always be the first to have automated testing. Thorough testing is highly recommended for expected and unexpected values since any bug could have potentially disastrous effect. Everything else can come later.

We have to be strict when deciding whether a feature is critical, or we might end up saying that 90% of the code is critical. Would a bug cause the app to crash? That's not critical. Would it make customer angry? That's not critical since it can be used as an excuse for every bug.

Bug Prone Code

Once all critical features are fully tested, we can move on to bug prone areas starting from the most likely to the least likely. Some of the factors that increase the chance of bugs are: amount of custom code, number inputs and outputs, logical complexity, high usage. That usually means testing high level functions such as controllers, instead of low level utility functions. This will let you get more code coverage with less tests, and also cover more flows, inputs and outputs. Functions which are made up of mostly third party party code will have lower priority since most of it are already be well tested. Features that are very frequently used should have higher priority simply because bug discovery is much more likely and more people will be affected by the bug. Compare this to a buggy feature that is barely used by anyone. There's a lower chance of discovering the bug. And even if the bug goes unnoticed, very few people would be affected by it. It is quite unnecessary to test functions that are simple and infrequently used since they are 1) less likely to be buggy, 2) less likely to be affected by code changes, 3) much easier to achieve 0 bug.

Since frequent usage increase the chance and impact of bug, it stands to reason that we should prioritize testing with data that users are more likely to enter. That means we should have lower priority for testing edge cases and bad input. Or simply not test them at all. For example, a user who enters his email in a date field might cause a horrifying error page, but he can easily rectify this by trying again and hopefully realizing this mistake. In the worst case, 1 user will have an unpleasant experience. Compare this to a user who enters the correct value into the correct field. There is simply no way to help himself. And everyone would be affected by it.

That's All

Since the goal is to write as little test as possible, any additional test means we waste more time and increase our technical debt. Hopefully with these guidelines we can write only 20% of the tests yet achieve 80% of the benefits of testing.

Keywords: unit testing, software testing, automated testing, programming

KPop Star Rain & Mediacorp Celebrities Red Carpet at Cartier - Ion

The Cartier flagship store at Ion Orchard has officially reopened and is now the largest boutique in South East Asia. There were special appearances by KPop star Rain and local celebrities Zoe Tay, Fann Wong, Christopher Lee, Rui En, Rebecca Lim and Sheila Sim.

Keywords: rain, mediacorp, celebrity, cartier, ion, opening, photography

Tiger Sugar Opening at Capitol Piazza

Popular Taichung brand Tiger Sugar has finally come to Singapore with the first store opening at Capitol Piazza. Creating the drink requires around 10 staff and 3 hours. The brand's emphasis on quality and authenticity extends to even the type of ice it uses. The shape of ice is similar to the ones typically drunk with whisky. The new store opened with a bang and a long queue that lasted over an hour.

Keywords: tiger sugar, opening, ceremony, event, lion dance, photographer

AIG Sentosa Golf Club and Tangling Rugby Club 2018

Some examples of official photographs from AIG Sentosa Golf Club and Tangling Rugby Club events held on 16 November and 17 November 2018.

Keywords: sports, youth, acitivity, photographer, event, photography, aig, golf, rubgy