Fix bin/magento taking all the RAM

While working with Magento 2.3.6 on Bixoto I hit a weird issue: the bin/magento command-line tool was always eating all the RAM, even with a simple command:

$ ./bin/magento --help
PHP Fatal error:  Allowed memory size of 2147483648 bytes exhausted (tried to allocate 262144 bytes) in /home/baptiste/.../vendor/magento/module-store/Model/Config/Placeholder.php on line 146
Check https://getcomposer.org/doc/articles/troubleshooting.md#memory-limit-errors for more info on how to handle out of memory errors.

The issue, as weird as it sounds, is an empty configuration value that causes Magento to end up in an infinite loop.

When I installed Magento on my local machine, I deactivated HTTPS by setting web/secure/base_url to NULL in the table core_config_data. This alone is the cause of the issue.

Check in MySQL:

SELECT * FROM core_config_data WHERE path = 'web/secure/base_url' LIMIT 1;

If this shows a line with a NULL value, either delete it or replace it with some non-null value:

UPDATE core_config_data SET value='http://...' WHERE path = 'web/secure/base_url' limit 1;

This has been reported to Magento but was closed because “it’s not a bug”. I don’t think falling in an infinite loop on --help because some config value is NULL should really be a normal behavior, but at least now you know how to solve it.

Fix Virtualbox installation for Docker on macOS

While following a tutorial to install Virtualbox in order to have docker working on macOS, I hit an issue where the docker-machine create command fails with an error that looks like this:

VBoxManage: error: Failed to create the host-only adapter
VBoxManage: error: VBoxNetAdpCtl: Error while adding new interface: failed to open /dev/vboxnetctl: No such file or directory
VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005), component HostNetworkInterfaceWrap, interface IHostNetworkInterface
VBoxManage: error: Context: "RTEXITCODE handleCreate(HandlerArg *)" at line 95 of file VBoxManageHostonly.cpp

If you search on the Web, everybody says you have to open the Security & Privacy settings window and allow the Oracle kernel extensions to run. But I didn’t have it. I tried uninstalling Virtualbox, re-installing through the official website, reboot, uninstall, re-install with brew cask but I always had the issue. Some people reported having a failed Virtualbox installation but mine seemed ok.

I tried the spctl solution but it didn’t change anything.

In the end, I tried this StackOverflow answer:

sudo "/Library/Application Support/VirtualBox/LaunchDaemons/VirtualBoxStartup.sh" restart

It failed, but it told me to check the Security & Privacy setting window. I did, and I had the button everyone was talking about. I enabled the kernel extension, rebooted, and it worked.

Hope this can save some time to anyone having the same issue!

Introduction to Code-Golf in Clojure

Code-Golf is the art of writing the shortest program in a given language that implements some given algorithm. It started in the 90’s in the Perl community and spread to other languages; there are now languages dedicated to code-golfing and StackExchange has a Q&A website for it.

In 2015, for example, I wrote a blog post showing how to write a JavaScript modules manager that fits in 140 chars (the maximum length of a tweet at that time).

4clojure is a well-known website to learn Clojure through exercises of increasing difficulty, but it has a lesser-known code-golf challenge which you can enable by clicking on “Leagues” in the top menu. If you check the code-golf checkbox, you then get a score on each problem that is the number of non-whitespace characters of your solution; the smaller the better.

The first thing you’ll note when code-golfing is that the reader syntax for anonymous functions is a lot shorter than using fn:

; 18 chars
(fn [a b c] (* (+ a b) c))

; 13 chars
#(* (+ %1 %2) %3)
; 12 chars: -1 char because '%' is equivalent to '%1'
#(* (+ % %2) %3)

Unfortunately you can’t have a reader-syntax function inside another reader-syntax one, so you often have to transform the code not to use anonymous functions.

for is a very powerful tool for that, because it allows you to do the equivalent of map, and a lot more, with no function:

; invalid!
#(map #(* 2 %) %)

; 19 chars
#(map (fn [x] (* 2 x)) %)
; 17 chars
#(map (partial * 2) %)
; 15 chars
#(for [x %] (* 2 x))

; Note that for this specific example
; the best solution uses `map`:
#(map + % %)

On some problems it can even be shorter than using map + filter:

; 31 chars
(fn [x a]
  (map inc (filter #(< % a) x)))

; 26 chars
#(for [e x :when (< e a)] (inc e))

Some core functions are equivalent in some contexts and so the shorter one can substitute a longer one:

; 18 chars
#(filter identity %)
; 14 chars
#(filter comp %)

; 6 chars
(inc x)
(dec x)
; 5 chars
(+ x 1)
(- x 1)

; 12 chars
(reduce str x)
; 11 chars
(apply str x)

; 14 chars
(apply concat x)
; 13 chars
(mapcat comp x)

When you must use a long function name in multiple places, it might be shorter to let that function with a one-letter symbol:

; 120 chars
#(clojure.set/difference
   (clojure.set/union % %2)
   (clojure.set/union
     (clojure.set/difference % %2)
     (clojure.set/difference %2 %)))

; 73 chars
#(let [d clojure.set/difference u clojure.set/union]
   (d (u % %2) (u (d % %2) (d %2 %))))

; Note that for this specific example
; there is a 17-chars solution
#(set (filter %2 %))

Other tricks

Use indexed access on vectors:

; 15 chars
(first [:a :b :c])
; 11 chars
([:a :b :c] 0)

Use set literals as functions:

; 16 chars
(remove #(= :a %) x)
; 14 chars
(remove #{:a} x)

Inverse conditions to use shorter functions:

; 15 chars
(if (empty? p) a b)
; 12 chars
(if (seq p) b a)

Inlined code is sometimes shorter:

; 24 chars
(let [p (* 3 a)]
  (if (< p 5)
    a
    p))
; 19 chars
(if (< (* 3 a) 5)
  a
  (* 3 a))

Use 1 instead of :else/:default in cond:

; 24 chars
(cond
  (= m p) a
  (< m p) b
  :else c)

; 20 chars
(cond
  (= m p) a
  (< m p) b
  1 c)

Use maps instead of ifs for conditions on equality (this one really makes the code harder to read):

; 13 chars
(if (= "L" x) a b)
; 12 chars
(case x "L" a b)
; 10 chars
({"L" a} x b)