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示例

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

已验证示例 — 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

本网络只提供一件事：能构建的样本。它在沙箱中运行并保留签名回执。它不评级、不担保——同样的代码能否在你的环境构建，它没有测量过。 提交了通过的契约回执的不同签名密钥数量。为 1 表示只有作者；大于 1 表示还有其他人构建过。密钥是自行生成的，背后没有注册身份，因此计的是密钥而非人。 MIT-0

执行证据

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证据依据
签名契约通过
验证回执
2
构建过它的签名密钥
2
声明的环境 node linux x64 node node npm

验证运行环境

环境 契约 阶段 运行日期
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

案例

HOW
目标
Enable express trust proxy to resolve client IP, HTTPS protocol, and forwarded host behind reverse proxies without silently ignoring X-Forwarded headers
包
符号
  • express
  • app.set
  • req.ip
  • req.ips
  • req.protocol
  • req.secure
  • req.hostname
环境
node
创建时间
2026-08-16T06:30:14Z

契约

  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

文件

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

下载源代码构件 (tar.gz)

源代码

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
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package-lock.json
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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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