journalctl — abhijithota.com

HyperLogLog

• https://alexharri.com/blog/typescript-structural-typing
• https://neugierig.org/software/blog/2019/11/interface-pattern.html

• Goroutines are lightweight threads

• Goroutines run in the same address space

  • What’s an address space?

    that’s saying that if you have concurrent access to shared memory you must synchronize it. More specifically, if we let A be a variable, you cannot have multiple goroutines reading and writing to A without synchronization

• Channels are the default structures to send and receive values between goroutines

  By default, sends and receives block until the other side is ready. This allows goroutines to synchronize without explicit locks or condition variables.

• The following code waits till c receives two values.

  x, y := <- c, <- c

  • Ask a clarifying question about how does it know when to block or not

    Sends to a buffered channel block only when the buffer is full. Receives block when the buffer is empty.

• time.Sleep is blocking

• If you want to add stuff to previous commits:

  # OLDCOMMIT is the commit hash like abcd123
  git add <my fixed files>
  git commit --fixup=OLDCOMMIT
  git rebase --interactive --autosquash OLDCOMMIT^

Courtesy: https://stackoverflow.com/a/27721031/12172493

Learnt about windows functions while trying to find out the answer to this question

If the code panics inside a function in Gin, it sends 500 instead of exiting the process! :chef’s kiss:

• afdfsf

• sff

• Using ImageMagick’s convert to merge two photos.

  • To merge vertically:

    convert input1.png input2.png -append output-that-is-created.png

    If your photos are of different width, you’ll likely get an ugly padding. As a workaround, you can limit the maximum width to be <= to the width of the photo with the minimum width like:

    convert input1.png input2.png input3.png input4.png -geometry x1000 -append output-that-is-created.png

    assuming the minimum width among the 4 inputs is <= 1000px.

  • To merge horizontally, +append instead of -append. The logic for padding and width constraint applies to heights here.

  • Using identify to get basic photo information:

    identify image1.png

• I stumbled upon this Postmark issue and so I made this gist to help.

  Used pup to parse the webpage along with jq. Here’s the command for doing what I achieved:

  cat downloaded.html \
  | pup 'json{}' \
  | jq '[.[].children[] | select(.tag == "strong" and .text != null) | .text] | map(split(" - ")) | map({ code: .[0], message: .[1] })' \
  > out.json

  Obviously, I won’t remember a lot so here’s a super cool jq cheat sheet

• The ::marker pseudo-element can be used for styling li markers.

• MongoDB $map operator is pretty cool.

• I wanted to update a MongoDB collection. A simple operation. Move all the items from one array field to an other array field. It resulted in 2 hours of documentation scouring but I finally got it.

  In MongoDB db.collection.update(), you have to specify the update query (the second paramter) as an array to pass it as a pipeline. Some operations won’t work including references to document fields with $ notation.

  Here’s the forum post I made and solved myself.

• Bash is pretty easy to learn but I still have to come across its whitespace nuances.

• The Rainbow Chart

• Google spent a lot of time and research into finding a SHA-1 collision. Here.

• https://news.ycombinator.com/item?id=14791255

• RSA works on the principle of how difficult it is to factorise large (like 617 digits large) numbers. More info here

• Redeemed Educative’s GitHub scholarship

• Applied to a copule of internships:

  • FamPay (found via LinkedIn)
  • Tilt (via AngelList)
  • Shortlisted a few FinTech startups

• SendGrid sucks. They put our account under review because we did not use it for a while. There were no pending payments whatsoever. Shifted to Postmark and Mailersend. Going to try them before shifting totally.

This is how you split a string: http://www.cplusplus.com/faq/sequences/strings/split/#string-find_first_of or best way using the std lib:

#include <sstream>
#include <iostream>
#include <vector>

using namespace std;

int main() {
    vector<string> strings;
    istringstream f("denmark;sweden;india;us");
    string s;
    while (getline(f, s, ';')) {
        cout << s << endl;
        strings.push_back(s);
    }
}

• MongoDB: You cannot mix inclusion and exclusion, the only exception is the _id field. Look here.
• JavaScript
  • Learnt about flatMap . Solved an SO question using that:

    const arr = [1, 2, 3, 4, 5];
    const str = arr
    	.flatMap((val, i, _arr) =>
    		i !== arr.length - 1 ? `${val} => ${_arr[i + 1]}` : []
    	)
    	.join(", ");
    console.log(str); // "1 => 2, 2 => 3, 3 => 4, 4 => 5"

    Going to use it instead of chaining filters and map.
• Some blogs I discovered
  • Daniel Stenberg (Creator of curl)
  • Matt Mullenburg
  • Martin Tournoij
  • Julia Evans

I accidentally cleared a production database…

I love StackOverflow.

This is my query:

const deleted = db
	.getCollection("oplog.rs")
	.find({ op: "d", ns: "e_summit_2021.users" }, { "o._id": 1 })
	.sort({ ts: -1 });

db.getCollection("oplog.rs")
	.find(
		{ op: "i", ns: "e_summit_2021.users", $in: { "o._id": deleted } },
		{ o: 1 }
	)
	.sort({ ts: -1 });

HNY!

Found this cool table:

,	/	:	;	=	?	@	[	]
%2C	%2F	%3A	%3B	%3D	%3F	%40	%5B	%5D

!	#	$	&	‘	(	)	*	+
%21	%23	%24	%26	%27	%28	%29	%2A	%2B

• Installed and integrated Cmder and successfully integrated it with Windows Terminal and VS Code. Loving it so far. This is exactly what I was looking for in a terminal on Windows!

• git pruning:

• git remote prune origin removes all the remote stale deleted branches. Use cases: Some branches remain in the origin/*** when you do a git branch -a. Pruning sort of cleans up the repository. I’ll be using this mostly.

  • git fetch -p prunes and fetches everything locally.

• Learnt (again) about Mongoose SchemaTypes. Clarified one thing:

  let mySchema = new mongoose.Schema({
  	name: String,
  	hobbies: [String],
  	friends: [{ name: String, hobbies: [String] }],
  });

  is same as

  let mySchema = new mongoose.Schema({
  	name: { type: String },
  	hobbies: [{ type: String }],
  	friends: [
  		{
  			name: { type: String },
  			hobbies: [{ type: String }],
  		},
  	],
  });