test-bug.js

#!/usr/bin/env node

// test-bug.js — Simulates a real-world bug: a config parser that crashes
// when required fields are missing from a JSON config file.

import { readFileSync } from "node:fs";
import { resolve } from "node:path";

function loadConfig(filePath) {
  const raw = readFileSync(resolve(filePath), "utf8");
  return JSON.parse(raw);
}

function validateConfig(config) {
  const required = ["database", "server", "auth"];
  const missing = [];

  for (const key of required) {
    if (!config[key]) {
      missing.push(key);
    }
  }

  if (missing.length > 0) {
    throw new Error(
      `Invalid config: missing required fields: ${missing.join(", ")}. ` +
      `Expected at least: ${required.join(", ")}. ` +
      `Got: ${Object.keys(config).join(", ") || "none"}`
    );
  }

  return config;
}

function setupDatabase(dbConfig) {
  if (!dbConfig.host || !dbConfig.port) {
    throw new TypeError(
      `Cannot connect to database: host and port are required. ` +
      `Received host="${dbConfig.host}", port=${dbConfig.port}`
    );
  }

  // Simulate connection attempt
  const connection = { connected: false, host: dbConfig.host, port: dbConfig.port };

  if (dbConfig.password === "wrong") {
    connection.error = new Error(
      `Authentication failed for user "${dbConfig.user}" on ${dbConfig.host}:${dbConfig.port}`
    );
  } else {
    connection.connected = true;
  }

  return connection;
}

// --- Main ---
try {
  const config = loadConfig("./test-config.json");
  const validated = validateConfig(config);
  const db = setupDatabase(validated.database);

  if (!db.connected) {
    throw db.error || new Error("Database connection failed for unknown reason");
  }

  console.log("Config loaded successfully:", JSON.stringify(validated, null, 2));
} catch (err) {
  console.error("FATAL: Application startup failed");
  console.error(`Error: ${err.message}`);
  console.error(`Code: ${err.code || "ERR_APP_STARTUP"}`);
  if (err.stack) {
    console.error("Stack trace:");
    console.error(err.stack);
  }
  process.exit(1);
}