Code Explainers

Browse the library

ruby 
class Order
  class InvalidTransition < StandardError; end
 
  TRANSITIONS = {

A state machine for order transitions in Ruby

state-machine data-driven error-handling
Intermediate 8 steps
python 
from flask import Blueprint, jsonify, request, abort
 
v1 = Blueprint("users_v1", __name__)
v2 = Blueprint("users_v2", __name__)

Versioning a Flask API with Blueprints

api versioning blueprints rest
Intermediate 7 steps
java 
public class SlidingLogRateLimiter {
 
    private final int maxRequests;
    private final long windowMillis;

How a sliding-log rate limiter works

rate-limiting concurrency sliding-window
Advanced 8 steps
typescript 
import { Injectable, UnauthorizedException } from '@nestjs/common';
import { PassportStrategy } from '@nestjs/passport';
import { ExtractJwt, Strategy } from 'passport-jwt';
import { ConfigService } from '@nestjs/config';

How a JWT strategy authenticates in NestJS

authentication jwt passport
Intermediate 7 steps
go 
package theme
 
import (
	"fmt"

Per-tenant HTML templates with Gin's renderer

multi-tenancy concurrency html-templates
Advanced 8 steps
rust 
use std::cmp::Ordering;
 
pub struct PrefixIndex {
    entries: Vec<String>,

Prefix search with binary partitioning in Rust

binary-search sorting case-insensitive
Intermediate 7 steps
php 
<?php
 
namespace App\Http\Controllers;
 

Streaming a filtered CSV export in Laravel

streaming csv-export query-builder
Intermediate 9 steps
javascript 
const express = require('express');
const router = express.Router();
const { pool } = require('../db');
const redis = require('../redis');

Building a health check endpoint in Express

health-check timeouts promise-race
Intermediate 9 steps
ruby 
class CreateOrderItems < ActiveRecord::Migration[7.1]
  def change
    create_table :order_items do |t|
      t.references :order, null: false, foreign_key: { on_delete: :cascade }

Enforcing order-item integrity in Rails

migrations foreign-keys validations
Intermediate 7 steps
python 
import time
import threading
from enum import Enum
from functools import wraps

Building a circuit breaker in Python

circuit-breaker resilience decorators
Advanced 7 steps
java 
public final class Slugifier {
 
    private static final Pattern NON_LATIN = Pattern.compile("[^\\w-]");
    private static final Pattern WHITESPACE = Pattern.compile("[\\s]+");

Building a URL slugifier in Java

regex unicode-normalization string-processing
Intermediate 8 steps
typescript 
import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent, HttpErrorResponse } from '@angular/common/http';
import { BehaviorSubject, Observable, throwError } from 'rxjs';
import { catchError, filter, take, switchMap } from 'rxjs/operators';

Refreshing auth tokens in an Angular interceptor

http-interceptor token-refresh rxjs
Advanced 8 steps
go 
package auth
 
import (
	"net/http"

Setting and reading secure session cookies in Go

cookies session-management security
Intermediate 6 steps
rust 
use std::cmp::Ordering;
use std::str::FromStr;
 
#[derive(Debug, Clone, PartialEq, Eq)]

Parsing and ordering semantic versions in Rust

parsing trait-implementation ordering
Intermediate 8 steps
php 
<?php
 
namespace App\Http\Middleware;
 

Idempotent requests with Laravel middleware

idempotency middleware caching
Advanced 8 steps
javascript 
'use client';
 
import { useEffect } from 'react';
import * as Sentry from '@sentry/nextjs';

How a Next.js error boundary recovers

error-boundary error-handling observability
Intermediate 8 steps
ruby 
class Registration < ApplicationRecord
  belongs_to :event
 
  validates :email, presence: true, format: { with: URI::MailTo::EMAIL_REGEXP }

Validating registrations in Rails

validations i18n error-handling
Intermediate 8 steps
python 
from django.contrib.postgres.search import SearchQuery, SearchRank, SearchVector
from django.core.cache import cache
from django.db.models import F
from django.http import JsonResponse

Ranked full-text search in Django

full-text-search debouncing caching
Advanced 9 steps