sentryagent-idp/tests/unit/middleware/metrics.test.ts

/**
 * Unit tests for src/middleware/metrics.ts
 *
 * Verifies that metricsMiddleware increments agentidp_http_requests_total
 * and records agentidp_http_request_duration_seconds with the correct labels
 * (method, route, status_code) on each request's 'finish' event.
 */

import { Request, Response, NextFunction } from 'express';
import { metricsMiddleware } from '../../../src/middleware/metrics';
import { metricsRegistry } from '../../../src/metrics/registry';

/**
 * prom-client 15 MetricValue does not expose `metricName` in its TypeScript
 * types, but histogram entries carry it at runtime to distinguish _count/_sum
 * from _bucket rows. This local interface allows the cast below.
 */
interface HistogramMetricValue {
  labels: Record<string, string>;
  value: number;
  metricName?: string;
}

// ────────────────────────────────────────────────────────────────────────────
// Helpers
// ────────────────────────────────────────────────────────────────────────────

/** Build a minimal mock Express Request. */
function makeMockRequest(overrides: Partial<Request> = {}): Request {
  return {
    method: 'GET',
    path: '/test',
    baseUrl: '',
    route: undefined,
    originalUrl: '/test',
    ...overrides,
  } as unknown as Request;
}

/**
 * Build a minimal mock Express Response that captures 'finish' callbacks
 * so we can trigger them manually.
 */
function makeMockResponse(statusCode = 200): { res: Response; triggerFinish: () => void } {
  const finishCallbacks: Array<() => void> = [];

  const res = {
    statusCode,
    on: (event: string, cb: () => void) => {
      if (event === 'finish') {
        finishCallbacks.push(cb);
      }
    },
  } as unknown as Response;

  return {
    res,
    triggerFinish: () => finishCallbacks.forEach((cb) => cb()),
  };
}

// ────────────────────────────────────────────────────────────────────────────
// Tests
// ────────────────────────────────────────────────────────────────────────────

describe('metricsMiddleware', () => {
  let next: jest.MockedFunction<NextFunction>;

  beforeEach(async () => {
    // Reset all metric values between tests to avoid cross-test pollution.
    metricsRegistry.resetMetrics();
    next = jest.fn();
  });

  it('calls next() immediately', () => {
    const req = makeMockRequest();
    const { res } = makeMockResponse();

    metricsMiddleware(req, res, next);

    expect(next).toHaveBeenCalledTimes(1);
  });

  it('does NOT increment counter before finish event fires', async () => {
    const req = makeMockRequest();
    const { res } = makeMockResponse();

    metricsMiddleware(req, res, next);

    const metricsBefore = await metricsRegistry.getMetricsAsJSON();
    const counterEntry = metricsBefore.find((e) => e.name === 'agentidp_http_requests_total');
    // No values recorded yet — values array will be empty
    expect(counterEntry?.values ?? []).toHaveLength(0);
  });

  it('increments agentidp_http_requests_total after finish event', async () => {
    const req = makeMockRequest({ method: 'POST', path: '/api/v1/agents' });
    const { res, triggerFinish } = makeMockResponse(201);

    metricsMiddleware(req, res, next);
    triggerFinish();

    const metricsJson = await metricsRegistry.getMetricsAsJSON();
    const counterEntry = metricsJson.find((e) => e.name === 'agentidp_http_requests_total');
    expect(counterEntry).toBeDefined();
    expect(counterEntry!.values).toHaveLength(1);

    const recorded = counterEntry!.values[0];
    expect(recorded.labels['method']).toBe('POST');
    expect(recorded.labels['status_code']).toBe('201');
    expect(recorded.value).toBe(1);
  });

  it('records agentidp_http_request_duration_seconds after finish event', async () => {
    const req = makeMockRequest({ method: 'GET', path: '/health' });
    const { res, triggerFinish } = makeMockResponse(200);

    metricsMiddleware(req, res, next);
    triggerFinish();

    const metricsJson = await metricsRegistry.getMetricsAsJSON();
    const histEntry = metricsJson.find(
      (e) => e.name === 'agentidp_http_request_duration_seconds',
    );
    expect(histEntry).toBeDefined();
    // Histogram produces _bucket, _count and _sum entries — count must be 1
    const countEntry = (histEntry!.values as HistogramMetricValue[]).find(
      (v) => v.metricName === 'agentidp_http_request_duration_seconds_count',
    );
    expect(countEntry).toBeDefined();
    expect(countEntry!.value).toBe(1);
  });

  it('uses matched route pattern when req.route.path is available', async () => {
    const req = makeMockRequest({
      method: 'GET',
      path: '/api/v1/agents/some-uuid',
      baseUrl: '/api/v1/agents',
      route: { path: '/:agentId' } as Request['route'],
    });
    const { res, triggerFinish } = makeMockResponse(200);

    metricsMiddleware(req, res, next);
    triggerFinish();

    const metricsJson = await metricsRegistry.getMetricsAsJSON();
    const counterEntry = metricsJson.find((e) => e.name === 'agentidp_http_requests_total');
    expect(counterEntry).toBeDefined();
    const recorded = counterEntry!.values[0];
    // Route should be baseUrl + route.path = '/api/v1/agents/:agentId'
    expect(recorded.labels['route']).toBe('/api/v1/agents/:agentId');
  });

  it('replaces UUID segments when no route pattern is available', async () => {
    const uuid = '123e4567-e89b-12d3-a456-426614174000';
    const req = makeMockRequest({
      method: 'DELETE',
      path: `/api/v1/agents/${uuid}`,
      baseUrl: '',
      route: undefined,
    });
    const { res, triggerFinish } = makeMockResponse(204);

    metricsMiddleware(req, res, next);
    triggerFinish();

    const metricsJson = await metricsRegistry.getMetricsAsJSON();
    const counterEntry = metricsJson.find((e) => e.name === 'agentidp_http_requests_total');
    expect(counterEntry).toBeDefined();
    const recorded = counterEntry!.values[0];
    expect(recorded.labels['route']).toBe('/api/v1/agents/:id');
    expect(recorded.labels['method']).toBe('DELETE');
    expect(recorded.labels['status_code']).toBe('204');
  });

  it('increments counter multiple times for multiple requests', async () => {
    for (let i = 0; i < 3; i++) {
      const req = makeMockRequest({ method: 'GET', path: '/health' });
      const { res, triggerFinish } = makeMockResponse(200);
      metricsMiddleware(req, res, next);
      triggerFinish();
    }

    const metricsJson = await metricsRegistry.getMetricsAsJSON();
    const counterEntry = metricsJson.find((e) => e.name === 'agentidp_http_requests_total');
    expect(counterEntry).toBeDefined();
    const recorded = counterEntry!.values[0];
    expect(recorded.value).toBe(3);
  });
});