Advanced code explainers

go

package streaming
 
import (
	"bufio"

Streaming NDJSON logs over HTTP in Go

http-streaming channels select

Advanced 10 steps

java

@Component
@Converter
public class EncryptedStringConverter implements AttributeConverter<String, String> {

Transparent column encryption in Spring & JPA

encryption aes-gcm jpa-converter

Advanced 10 steps

rust

use axum::{
    extract::{Path, State},
    response::sse::{Event, KeepAlive, Sse},
};

Streaming import progress with SSE in Axum

server-sent-events streams watch-channel

Advanced 7 steps

javascript

import { useState, useEffect, useCallback, useRef } from 'react';
 
const cache = new Map();
const inflight = new Map();

Building a stale-while-revalidate hook in React

caching request-deduplication custom-hooks

Advanced 10 steps

go

func (w *Watcher) resetDebounce(d time.Duration) {
	if !w.timer.Stop() {
		select {
		case <-w.timer.C:

Debouncing a stream of events in Go

debounce timers channels

Advanced 7 steps

rust

use std::collections::VecDeque;
use std::sync::{Arc, Condvar, Mutex};
use std::time::{Duration, Instant};

Building a counting semaphore in Rust

concurrency synchronization condition-variable

Advanced 9 steps

typescript

import { Injectable, Scope, Inject, NotFoundException } from '@nestjs/common';
import { REQUEST } from '@nestjs/core';
import { Request } from 'express';
import { DataSource } from 'typeorm';

Per-tenant database connections in NestJS

multi-tenancy connection-pooling dependency-injection

Advanced 8 steps

rust

use std::time::Duration;
use tokio::sync::mpsc;
use tokio::time::{interval, MissedTickBehavior};

A token-bucket rate limiter in Tokio

rate-limiting channels async

Advanced 8 steps

ruby

class Coupon < ApplicationRecord
  has_many :redemptions, dependent: :destroy
 
  validates :code, presence: true, uniqueness: { case_sensitive: false }

Safe coupon redemption in Rails

validation contexts pessimistic locking scopes

Advanced 10 steps

javascript

const { pool } = require('./db');
 
function withTransaction() {
  return async (req, res, next) => {

A per-request transaction middleware in Express

middleware database-transactions connection-pooling

Advanced 7 steps

rust

use axum::{
    extract::FromRequestParts,
    http::{request::Parts, HeaderMap, StatusCode},
};

Building a replay-guard extractor in Axum

custom-extractor replay-protection shared-state

Advanced 8 steps

go

type Counter struct {
	counts sync.Map
}

A concurrent counter with sync.Map in Go

concurrency atomics sync.map

Advanced 8 steps

typescript

import { useCallback, useRef, useState } from "react";
 
type Tag = { id: string; label: string };

A debounced, abortable tag-input hook in React

custom-hooks debounce abort-controller

Advanced 10 steps

ruby

require "openssl"
require "base64"
 
module SecureToken

Authenticated encryption with AES-GCM in Ruby

encryption aes-gcm authentication

Advanced 8 steps

javascript

class Sheet {
  constructor() {
    this.cells = new Map();
    this.computing = new Set();

Building a reactive spreadsheet engine

reactivity dependency-tracking graph-traversal

Advanced 9 steps

javascript

const express = require('express');
const router = express.Router();
 
router.get('/exports/orders', async (req, res) => {

Streaming a large JSON export in Express

streaming backpressure cursors

Advanced 9 steps

python

import asyncio
import logging
from dataclasses import dataclass

A concurrent batch geocoder in asyncio

asyncio producer-consumer rate-limiting

Advanced 8 steps

javascript

const crypto = require('crypto');
 
function idempotency({ store, ttlMs = 24 * 60 * 60 * 1000 }) {
  return async function idempotencyMiddleware(req, res, next) {

Idempotent POST requests in Express

idempotency middleware caching

Advanced 8 steps