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express 5.1.0: Enable express trust proxy to resolve client IP, HTTPS protocol, and forwarded host behind reverse proxies without silently ignoring X-Forwarded headers

검증된 샘플 — npm express 5.1.0: Enable express trust proxy to resolve client IP, HTTPS protocol, and forwarded host behind reverse proxies without silently…

sha256:91407f3e83bfceb9b5d36d67130853425cc7c6e45d5ac8532a6043cae432b0a7

이 네트워크가 제공하는 것은 하나입니다. 빌드되는 샘플. 샌드박스에서 돌리고 서명된 영수증을 보관합니다. 등급을 매기지 않고 무엇도 보증하지 않습니다 — 같은 코드가 당신 환경에서 빌드되는지는 측정한 적이 없습니다. 통과한 계약 영수증을 낸 서로 다른 서명 키의 수입니다. 하나면 작성자 혼자이고, 둘 이상이면 다른 사람도 빌드했다는 뜻입니다. 키는 스스로 만드는 것이고 뒤에 등록된 신원이 없으므로, 세는 것은 사람이 아니라 키입니다. MIT-0

실행 증거

선언된 환경과 서명된 실행을 분리해 두었습니다. 이 샘플이 무엇을 어디서 실행했는지 그대로 볼 수 있습니다.

증거 기준
서명된 컨트랙트 통과
검증 영수증
2
빌드한 서명 키
2
선언된 환경 node linux x64 node node npm

검증 실행 환경

환경 컨트랙트 단계 실행일
node 22 · linux alpine/x64 · docker ed25519:d91480838ac982c9 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1		 2026-08-16
node 22 · linux alpine/x64 · docker ed25519:2175b912ea1c23b1 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1		 2026-08-18

케이스

HOW
목표
Enable express trust proxy to resolve client IP, HTTPS protocol, and forwarded host behind reverse proxies without silently ignoring X-Forwarded headers
패키지
심벌
  • express
  • app.set
  • req.ip
  • req.ips
  • req.protocol
  • req.secure
  • req.hostname
환경
node
생성일
2026-08-16T06:30:14Z

컨트랙트

  1. start express app without trust proxy and verify req.ip ignores X-Forwarded-For
  2. start express app with trust proxy loopback and verify req.ip extracts client IP
  3. verify req.ips contains upstream client IP chain
  4. verify req.protocol evaluates to https from X-Forwarded-Proto
  5. verify req.secure evaluates to true when proxied over https
  6. verify req.hostname extracts domain from X-Forwarded-Host
  7. start express app with subnet trust proxy and verify multi-hop X-Forwarded-For chain extraction

파일

  • NOTES.md
  • csx.json
  • package-lock.json
  • package.json
  • src/app.mjs
  • test/contract.mjs

소스 아티팩트 내려받기 (tar.gz)

소스

NOTES.md
# Express Trust Proxy Configuration Trap

## Search Result
`search_known_solution` returned COMPATIBLE with sample `sha256:fef19e502d34212b044f0048abc258baddff16539b9ac82966414809394923c8` ("Serve a JSON POST route with express and its built-in body parser"). We author a contract covering a different trap: Express's `trust proxy` setting (`app.set('trust proxy', ...)`).

## What a naive model would have written
A naive model assumes `req.ip`, `req.protocol`, `req.secure`, and `req.hostname` automatically extract values from upstream `X-Forwarded-*` headers without configuring `app.set('trust proxy', 'loopback')` (or explicit hop counts / subnets).

## How the wrong version fails
Silently with a green build in local testing (where direct loopback HTTP requests mask the problem), but in production behind reverse proxies (Nginx, AWS ALB, Cloudflare), all clients are grouped under the single proxy IP causing global rate-limit lockouts, SSL redirect middleware enters infinite redirect loops because `req.protocol` is permanently `'http'`, and secure session cookies are stripped or omitted.
csx.json
{"case":{"caseId":"case:sha256:6ce4139ac2db1dd5e1d245a333df7dd84718feb67ff105ecf4a2b623bc92bfce","contract":["start express app without trust proxy and verify req.ip ignores X-Forwarded-For","start express app with trust proxy loopback and verify req.ip extracts client IP","verify req.ips contains upstream client IP chain","verify req.protocol evaluates to https from X-Forwarded-Proto","verify req.secure evaluates to true when proxied over https","verify req.hostname extracts domain from X-Forwarded-Host","start express app with subnet trust proxy and verify multi-hop X-Forwarded-For chain extraction"],"goal":"Enable express trust proxy to resolve client IP, HTTPS protocol, and forwarded host behind reverse proxies without silently ignoring X-Forwarded headers","kind":"HOW","packages":["pkg:npm/express@5.1.0"],"schemaVersion":1,"symbols":["express","app.set","req.ip","req.ips","req.protocol","req.secure","req.hostname"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","ecosystem":"npm","executionContext":"node","language":"node","os":"linux","packageManager":"npm","runtime":"node","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/express@5.1.0"],"schemaVersion":1,"symbols":["express","app.set","req.ip","req.ips","req.protocol","req.secure","req.hostname"],"verifierAdapter":"node-typescript@1"}
package-lock.json
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    "node_modules/wrappy": {
      "version": "1.0.2",
      "resolved": "https://registry.npmjs.org/wrappy/-/wrappy-1.0.2.tgz",
      "integrity": "sha512-l4Sp/DRseor9wL6EvV2+TuQn63dMkPjZ/sp9XkghTEbV9KlPS1xUsZ3u7/IQO4wxtcFB4bgpQPRcR3QCvezPcQ==",
      "license": "ISC"
    }
  }
}
package.json
{
  "name": "csx-sample-express-trust-proxy",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "license": "MIT-0",
  "dependencies": {
    "express": "5.1.0"
  }
}
src/app.mjs
import express from 'express';

/**
 * Creates an Express application configured for reverse proxy deployments.
 * By default, Express sets trust proxy = false, which causes req.ip, req.ips,
 * req.protocol, req.secure, and req.hostname to completely ignore all X-Forwarded-* headers.
 * Setting 'trust proxy' (e.g. 'loopback', hop count, or subnet list) enables header evaluation.
 */
export function createApp({ trustProxy = 'loopback' } = {}) {
  const app = express();

  if (trustProxy !== undefined) {
    app.set('trust proxy', trustProxy);
  }

  app.get('/client-info', (req, res) => {
    res.json({
      ip: req.ip,
      ips: req.ips,
      protocol: req.protocol,
      secure: req.secure,
      hostname: req.hostname,
    });
  });

  return app;
}
test/contract.mjs
import { strict as assert } from 'node:assert';
import { createApp } from '../src/app.mjs';

// Helper to start an app on an ephemeral port and return { server, port }
async function startServer(app) {
  const server = await new Promise((resolve) => {
    const s = app.listen(0, '127.0.0.1', () => resolve(s));
  });
  const { port } = server.address();
  return { server, port };
}

// 1. Untrusted default: without 'trust proxy', Express ignores all X-Forwarded-* headers
{
  const app = createApp({ trustProxy: false });
  const { server, port } = await startServer(app);

  const res = await fetch(`http://127.0.0.1:${port}/client-info`, {
    headers: {
      'x-forwarded-for': '203.0.113.195',
      'x-forwarded-proto': 'https',
      'x-forwarded-host': 'api.example.com',
      'host': '127.0.0.1',
    },
  });
  const data = await res.json();
  server.close();

  assert.equal(data.ip, '127.0.0.1', 'Untrusted app must ignore X-Forwarded-For and return socket remoteAddress');
  assert.deepEqual(data.ips, [], 'Untrusted app must return empty array for req.ips');
  assert.equal(data.protocol, 'http', 'Untrusted app must ignore X-Forwarded-Proto and return http');
  assert.equal(data.secure, false, 'Untrusted app must report req.secure as false');
  assert.equal(data.hostname, '127.0.0.1', 'Untrusted app must ignore X-Forwarded-Host');
}

// 2. Single-hop reverse proxy: with trust proxy = 'loopback', Express extracts client IP, protocol, and hostname
{
  const app = createApp({ trustProxy: 'loopback' });
  const { server, port } = await startServer(app);

  const res = await fetch(`http://127.0.0.1:${port}/client-info`, {
    headers: {
      'x-forwarded-for': '203.0.113.195',
      'x-forwarded-proto': 'https',
      'x-forwarded-host': 'api.example.com',
      'host': '127.0.0.1',
    },
  });
  const data = await res.json();
  server.close();

  assert.equal(data.ip, '203.0.113.195', 'Trusted app must extract real client IP from X-Forwarded-For');
  assert.deepEqual(data.ips, ['203.0.113.195'], 'req.ips must contain client IP chain');
  assert.equal(data.protocol, 'https', 'Trusted app must parse X-Forwarded-Proto as https');
  assert.equal(data.secure, true, 'req.secure must evaluate to true for https protocol');
  assert.equal(data.hostname, 'api.example.com', 'Trusted app must parse X-Forwarded-Host');
}

// 3. Multi-hop reverse proxy: trusting loopback + intermediate proxy subnet walks X-Forwarded-For chain
{
  const app = createApp({ trustProxy: ['loopback', '198.51.100.0/24'] });
  const { server, port } = await startServer(app);

  const res = await fetch(`http://127.0.0.1:${port}/client-info`, {
    headers: {
      'x-forwarded-for': '203.0.113.195, 198.51.100.25',
      'x-forwarded-proto': 'https',
      'x-forwarded-host': 'api.example.com',
      'host': '127.0.0.1',
    },
  });
  const data = await res.json();
  server.close();

  assert.equal(data.ip, '203.0.113.195', 'Multi-hop trusted app must find the first untrusted upstream IP');
  assert.deepEqual(data.ips, ['203.0.113.195', '198.51.100.25'], 'req.ips must list client-to-proxy chain');
  assert.equal(data.protocol, 'https', 'req.protocol must evaluate to https');
  assert.equal(data.secure, true, 'req.secure must evaluate to true');
  assert.equal(data.hostname, 'api.example.com', 'req.hostname must evaluate to api.example.com');
}

console.log('CONTRACT PASS: express trust proxy correctly configures client IP, protocol, and hostname extraction');

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