Contextual Logging — Enriching Logs with Request and User Context

// Async Local Storage context
const { AsyncLocalStorage } = require('async_hooks');
const logContext = new AsyncLocalStorage();

function contextMiddleware(req, res, next) {
  const context = {
    correlationId: req.correlationId || uuidv4(),
    userId: req.user?.id,
    sessionId: req.session?.id,
    tenantId: req.tenant?.id,
    ip: req.ip,
    userAgent: req.headers['user-agent'],
    requestId: uuidv4(),
    startTime: Date.now()
  };

  logContext.run(context, () => next());
}

// Context-aware logger
const contextualLogger = {
  info: (message, data = {}) => {
    const ctx = logContext.getStore() || {};
    logger.info({
      ...ctx,
      message,
      ...data,
      timestamp: new Date().toISOString(),
      duration: ctx.startTime ? Date.now() - ctx.startTime : undefined
    });
  },

  error: (message, error, data = {}) => {
    const ctx = logContext.getStore() || {};
    logger.error({
      ...ctx,
      message,
      error: {
        name: error?.name,
        message: error?.message,
        stack: error?.stack?.split('\n').slice(0, 5)
      },
      ...data,
      timestamp: new Date().toISOString()
    });
  },

  warn: (message, data = {}) => {
    const ctx = logContext.getStore() || {};
    logger.warn({ ...ctx, message, ...data, timestamp: new Date().toISOString() });
  }
};

// Usage anywhere in request lifecycle
app.get('/api/scans', async (req, res) => {
  contextualLogger.info('Fetching scans', { filter: req.query.filter });
  const scans = await scanService.getAll();
  contextualLogger.info(`Found ${scans.length} scans`);
  res.json(scans);
});