feat: add news cache metrics

Author: Your Name

src/metrics/register.ts

@@ -1,4 +1,4 @@
-import { Registry, Counter, collectDefaultMetrics } from "prom-client";
+import { Registry, Counter, Histogram, collectDefaultMetrics } from "prom-client";
 
 export const register = new Registry();
 
@@ -10,3 +10,25 @@ export const httpRequestsTotal = new Counter({
   labelNames: ["method", "status_code"],
   registers: [register],
 });
+
+export const cacheEventsTotal = new Counter({
+  name: "news_cache_events_total",
+  help: "Total news search cache lookups by result",
+  labelNames: ["result"],
+  registers: [register],
+});
+
+export const upstreamRequestsTotal = new Counter({
+  name: "news_upstream_requests_total",
+  help: "Total upstream news provider requests by outcome",
+  labelNames: ["outcome"],
+  registers: [register],
+});
+
+export const upstreamRequestDurationSeconds = new Histogram({
+  name: "news_upstream_request_duration_seconds",
+  help: "Duration of upstream news provider requests in seconds",
+  labelNames: ["outcome"],
+  buckets: [0.05, 0.1, 0.25, 0.5, 1, 2, 5, 10, 15],
+  registers: [register],
+});

src/services/newsService.ts

@@ -4,6 +4,11 @@ import { HttpError } from "../errors/HttpError";
 import { getCacheStore } from "../cache/store";
 import { UPSTREAM_TIMEOUT_MS } from "../config/upstream";
 import { ArticleSearchFilters, ArticleSearchOptions } from "../types/search";
+import {
+  cacheEventsTotal,
+  upstreamRequestDurationSeconds,
+  upstreamRequestsTotal,
+} from "../metrics/register";
 
 const API_KEY = process.env.GNEWS_API_KEY;
 const BASE_URL = "https://gnews.io/api/v4";
@@ -50,25 +55,36 @@ export const fetchArticles = async (options: ArticleSearchOptions): Promise<Arti
   const store = getCacheStore();
   const cached = await store.get(cacheKey);
   if (cached) {
+    cacheEventsTotal.inc({ result: "hit" });
     return cached as Article[];
   }
+  cacheEventsTotal.inc({ result: "miss" });
 
+  const stopUpstreamTimer = upstreamRequestDurationSeconds.startTimer();
+  let articles: Article[];
   try {
     const response = await axios.get<{ articles: Article[] }>(`${BASE_URL}/search`, {
       params: toProviderParams(options),
       timeout: UPSTREAM_TIMEOUT_MS,
       validateStatus: (s) => s >= 200 && s < 300,
     });
 
-    const articles = normalizeArticles(response.data);
-    await store.set(cacheKey, articles);
-    return articles;
+    articles = normalizeArticles(response.data);
+    upstreamRequestsTotal.inc({ outcome: "success" });
+    stopUpstreamTimer({ outcome: "success" });
   } catch (err) {
+    const outcome =
+      err instanceof HttpError && err.statusCode === 502 ? "invalid_payload" : "error";
+    upstreamRequestsTotal.inc({ outcome });
+    stopUpstreamTimer({ outcome });
     if (axios.isAxiosError(err)) {
       throw new HttpError(502, "Upstream news service unavailable");
     }
     throw err;
   }
+
+  await store.set(cacheKey, articles);
+  return articles;
 };
 
 export const fetchArticlesByTitle = async (title: string): Promise<Article | undefined> => {

test/app.test.ts

@@ -135,6 +135,22 @@ describe("app", () => {
     expect(mockGet).toHaveBeenCalledTimes(1);
   });
 
+  it("records cache and upstream metrics for article searches", async () => {
+    mockGet.mockResolvedValue({ data: { articles: sampleArticles } });
+    const q = `metrics-${Math.random().toString(36).slice(2)}`;
+    await request(app).get(`/api/articles?query=${encodeURIComponent(q)}&count=2`);
+    await request(app).get(`/api/articles?query=${encodeURIComponent(q)}&count=2`);
+
+    const res = await request(app).get("/metrics");
+    expect(res.status).toBe(200);
+    expect(res.text).toContain('news_cache_events_total{result="miss"}');
+    expect(res.text).toContain('news_cache_events_total{result="hit"}');
+    expect(res.text).toContain('news_upstream_requests_total{outcome="success"}');
+    expect(res.text).toContain(
+      'news_upstream_request_duration_seconds_bucket{le="0.05",outcome="success"}'
+    );
+  });
+
   it("GET /api/articles/title returns article when matched", async () => {
     mockGet.mockResolvedValueOnce({ data: { articles: sampleArticles } });
     const title = encodeURIComponent("Alpha headline");