express-oom-middleware

Express middleware to reject requests and avoid out of memory (OOM) crashes

requirements

• Node v18.16.0+

usage

npm i @xplora-uk/express-oom-middleware

Shorter version:

import express from 'express';
import { makeExpressMiddleware } from '@xplora-uk/express-oom-middleware';

const app = express();
app.use(makeExpressMiddleware({
  memoryUsageLimit: 1024 * 1024 * 1024,
  //httpStatusCode: 500,
  //makeResponsePayload: () => ({ error: 'server is busy', ts: new Date() })
}));
app.get('/', (_req, res) => res.json({ ok: true }));

Longer version:

import express from 'express';
import { MemoryTracker, RequestRejector } from '@xplora-uk/express-oom-middleware';

const app = express();

const oneGB = 1024 * 1024 * 1024;
const mt = new MemoryTracker({ memoryUsageLimit: oneGB });
const rr = new RequestRejector(mt, {
  //httpStatusCode: 500,
  //makeResponsePayload: () => ({ error: 'server is busy', ts: new Date() })
});

app.use(rr.makeMiddleware());

app.get('/', (_req, res) => res.json({ ok: true }));

maintenance

installation

npm i

code

src/
  __tests__/
    component/
      express.test.ts          component tests for express middleware
      RequestRejector.test.ts  component tests for RequestRejector
    unit/
      MemoryTracker.test.ts    unit tests for MemoryTracker
  index.ts                     main file that exports features of this library
  express.ts                   file for express middleware - shortcut
  MemoryTracker.ts             MemoryTracker can give info about heap memory
  RequestRejector              RequestRejector uses MemoryTracker and creates an express middleware

build

npm run build

tests

You can run tests with/without coverage info.

npm run test:unit
npm run test:component
npm run test:coverage

Current coverage:

--------------------|---------|----------|---------|---------|-------------------
File                | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
--------------------|---------|----------|---------|---------|-------------------
All files           |     100 |    72.72 |     100 |     100 |                   
 MemoryTracker.ts   |     100 |    57.14 |     100 |     100 | 16-18             
 RequestRejector.ts |     100 |    77.77 |     100 |     100 | 27-28             
 express.ts         |     100 |    83.33 |     100 |     100 | 7                 
--------------------|---------|----------|---------|---------|-------------------

publish

It is important to increment version number using semantic versioning in package.json and re-create package-lock.json

# https://docs.npmjs.com/cli/v9/commands/npm-login
# using a member in xplora-uk
npm login

# https://docs.npmjs.com/cli/v9/commands/npm-publish
npm publish --access public