Record Request Timing Metrics: Code Review Practice

We have no per-endpoint latency data, so slow routes only show up as customer complaints. This adds middleware that times every request and records it in a histogram labeled by method, route pattern, and status code. Unmatched paths share one "unmatched" label so raw URLs never become label values. The existing /metrics endpoint exposes it.

Aapi/middleware/requestTiming.ts1 of 3

Files Changed

api/middleware/

api/

api/middleware/requestTiming.ts

TypeScript · Click a line number to comment · Tap a line to comment

@@ -0,0 +1,25 @@

import type { NextFunction, Request, Response } from "express";

import { Histogram } from "prom-client";

export const requestDuration = new Histogram({

name: "http_request_duration_ms",

help: "HTTP request duration in milliseconds",

labelNames: ["method", "route", "status"],

buckets: [5, 10, 25, 50, 100, 250, 500, 1000, 2500, 5000],

});

export function requestTiming(req: Request, res: Response, next: NextFunction) {

const start = process.hrtime.bigint();

res.on("finish", () => {

const ms = Number(process.hrtime.bigint() - start) / 1e6;

requestDuration.observe(

{

method: req.method,

route: req.route?.path ?? "unmatched",

status: String(res.statusCode),

ms,

);

});

next();

}

api/middleware/requestTiming.ts

api/app.ts

api/middleware/requestTiming.test.ts