Code Explainers

Browse the library

java 
package com.example.monitoring;
 
import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;

A custom replica health check in Spring

health-check actuator monitoring
Intermediate 7 steps
javascript 
import { NextResponse } from 'next/server';
import Stripe from 'stripe';
import { headers } from 'next/headers';
 

Handling Stripe webhooks in Next.js

webhooks signature verification payment processing
Intermediate 7 steps
go 
func StreamMetrics(c *gin.Context) {
	clientGone := c.Request.Context().Done()
	ticker := time.NewTicker(time.Second)
	defer ticker.Stop()

Streaming server-sent events in Gin

server-sent-events streaming channels
Intermediate 7 steps
php 
<?php
 
namespace App\Http\Middleware;
 

Enforcing a JSON Accept header in Laravel

middleware content-negotiation http-headers
Beginner 5 steps
python 
from fastapi import APIRouter, Depends, Query
from pydantic import BaseModel
from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession

How a paginated list endpoint works in FastAPI

pagination dependency-injection async-orm
Intermediate 8 steps
javascript 
const fs = require('fs');
const path = require('path');
 
router.get('/downloads/:name', (req, res, next) => {

Streaming file downloads in Express

streaming backpressure file-download
Advanced 9 steps
ruby 
module Retryable
  class RetriesExhausted < StandardError; end
 
  RETRYABLE_ERRORS = [

Exponential backoff retries in Ruby

retry-logic exponential-backoff error-handling
Intermediate 7 steps
typescript 
import { IsEmail, IsEnum, IsInt, IsOptional, IsString, Length, Max, Min } from 'class-validator';
import { Type } from 'class-transformer';
import { Body, Controller, Post } from '@nestjs/common';
 

How DTO validation works in NestJS

validation data-transfer-objects decorators
Intermediate 8 steps
go 
package worker
 
import (
	"fmt"

A graceful worker pool in Go

concurrency goroutines channels
Intermediate 7 steps
java 
@Repository
public interface OrderRepository extends JpaRepository<Order, Long> {
 
    @QueryHints(@QueryHint(name = HINT_FETCH_SIZE, value = "1000"))

Streaming large result sets in Spring Data JPA

streaming jpa memory-management
Advanced 6 steps
javascript 
async function pollJobUntilComplete(jobId, { interval = 2000, timeout = 60000, signal } = {}) {
  const deadline = Date.now() + timeout;
 
  while (true) {

Polling a job until it finishes in JavaScript

polling async-await abortsignal
Intermediate 6 steps
ruby 
class Throttle
  def initialize(interval)
    @interval = interval
    @mutex = Mutex.new

A thread-safe throttle in Ruby

concurrency rate-limiting mutex
Intermediate 7 steps
typescript 
type CheckoutState = "cart" | "shipping" | "payment" | "review" | "confirmed";
 
type CheckoutEvent =
  | { type: "PROCEED" }

A typed checkout state machine in TypeScript

state-machine union-types type-safety
Intermediate 7 steps
go 
package handlers
 
import (
	"net/http"

Rendering HTML pages with Gin handlers

http-handlers templating error-handling
Beginner 8 steps
rust 
use axum::{
    body::Body,
    extract::Path,
    http::{header, StatusCode},

Streaming file downloads in Axum

streaming file-serving path-traversal
Intermediate 8 steps
java 
import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;

Three ways to deduplicate a list by key in Java

streams deduplication collectors
Intermediate 6 steps
php 
<?php
 
function verifyJwt(string $token, string $secret): array
{

Verifying an HS256 JWT in PHP

jwt hmac authentication
Intermediate 9 steps
python 
from fastapi import FastAPI, Request, status
from fastapi.responses import JSONResponse
 
app = FastAPI()

Custom exception handlers in FastAPI

exception handling error responses separation of concerns
Intermediate 7 steps