feat(backend-sep24): [sep-24] log detailed interaction metrics to prometheus

backend/src/api/middleware/sep24-metrics.middleware.ts

@@ -0,0 +1,23 @@
+import { Request, Response, NextFunction } from 'express';
+import { recordSep24InteractionRequest } from '../../services/sep24-metrics.service';
+
+/**
+ * Middleware that records SEP-24 interactive endpoint duration and request counts
+ * to Prometheus.
+ */
+export function sep24MetricsMiddleware(
+  req: Request,
+  res: Response,
+  next: NextFunction,
+): void {
+  const start = Date.now();
+  const method = req.method;
+  const endpoint = req.route?.path ?? req.path;
+
+  res.on('finish', () => {
+    const durationSeconds = (Date.now() - start) / 1000;
+    recordSep24InteractionRequest(endpoint, method, res.statusCode, durationSeconds);
+  });
+
+  next();
+}

backend/src/api/routes/sep24.route.ts

@@ -9,10 +9,12 @@ import {
 } from '../../services/kyc.service';
 import prisma from '../../lib/prisma';
 import { isValidStellarPublicKey } from '../../utils/stellar-address';
-import { Sep24Service } from '../../services/sep24.service';
+import { sep24MetricsMiddleware } from '../middleware/sep24-metrics.middleware';
 
 const router = Router();
 
+router.use(sep24MetricsMiddleware);
+
 interface InteractiveRequest {
   asset_code: string;
   account?: string;

backend/src/services/sep24-metrics.service.test.ts

@@ -0,0 +1,31 @@
+import { metricsService } from './metrics.service';
+import { recordSep24InteractionRequest } from './sep24-metrics.service';
+
+describe('SEP-24 metrics', () => {
+  beforeEach(() => {
+    metricsService.reset();
+  });
+
+  it('registers interaction request counter and duration histogram', async () => {
+    const metrics = await metricsService.getMetrics();
+
+    expect(metrics).toContain('sep24_interaction_requests_total');
+    expect(metrics).toContain('sep24_interaction_endpoint_duration_seconds');
+  });
+
+  it('records interaction endpoint duration and request count', async () => {
+    recordSep24InteractionRequest(
+      '/transactions/deposit/interactive',
+      'POST',
+      200,
+      0.125,
+    );
+
+    const metrics = await metricsService.getMetrics();
+
+    expect(metrics).toContain('endpoint="/transactions/deposit/interactive"');
+    expect(metrics).toContain('method="POST"');
+    expect(metrics).toContain('status_code="200"');
+    expect(metrics).toContain('sep24_interaction_endpoint_duration_seconds_count');
+  });
+});

backend/src/services/sep24-metrics.service.ts

@@ -0,0 +1,33 @@
+import promClient, { Counter, Histogram } from 'prom-client';
+import { metricsService } from './metrics.service';
+
+const sep24InteractionRequestsTotal = new Counter({
+  name: 'sep24_interaction_requests_total',
+  help: 'Total number of SEP-24 interactive endpoint requests',
+  labelNames: ['endpoint', 'method', 'status_code'] as const,
+  registers: [metricsService.getRegistry()],
+});
+
+const sep24InteractionEndpointDuration = new Histogram({
+  name: 'sep24_interaction_endpoint_duration_seconds',
+  help: 'Duration of SEP-24 interactive endpoint requests in seconds',
+  labelNames: ['endpoint', 'method', 'status_code'] as const,
+  buckets: [0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10],
+  registers: [metricsService.getRegistry()],
+});
+
+export function recordSep24InteractionRequest(
+  endpoint: string,
+  method: string,
+  statusCode: number,
+  durationSeconds: number,
+): void {
+  const labels = {
+    endpoint,
+    method,
+    status_code: String(statusCode),
+  };
+
+  sep24InteractionRequestsTotal.inc(labels);
+  sep24InteractionEndpointDuration.observe(labels, durationSeconds);
+}