Next.js App Router can't handle proxied requests

[Smolya]

Checks

• I understand project setup issues should be asked on StackOverflow or in GitHub Discussions.
• I updated to latest http-proxy-middleware.

Describe the bug (be clear and concise)

I'm using App Router (next 13) and trying to proxy requests on another server via createProxyMiddleware. But I've got an error by doing this. I use example from https://github.com/chimurai/http-proxy-middleware/blob/master/recipes/servers.md#nextjs, but fitted to a new App Routes with GET and POST handlers
Error:

TypeError: Cannot set property url of #<NextRequest> which has only a getter
    at Object.set (webpack-internal:///(sc_server)/./node_modules/next/dist/server/future/route-modules/app-route/helpers/proxy-request.js:117:26)
    at HttpProxyMiddleware.applyPathRewrite (webpack-internal:///(sc_server)/./node_modules/http-proxy-middleware/dist/http-proxy-middleware.js:113:29)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async HttpProxyMiddleware.prepareProxyRequest (webpack-internal:///(sc_server)/./node_modules/http-proxy-middleware/dist/http-proxy-middleware.js:93:13)
    at async HttpProxyMiddleware.middleware (webpack-internal:///(sc_server)/./node_modules/http-proxy-middleware/dist/http-proxy-middleware.js:23:48)
    at async eval (webpack-internal:///(sc_server)/./node_modules/next/dist/server/future/route-modules/app-route/module.js:265:37)

Step-by-step reproduction instructions

- api/internal/[...path]/route.ts

import type { NextApiRequest, NextApiResponse } from 'next';
import {
    createProxyMiddleware,
} from 'http-proxy-middleware';

const proxy = createProxyMiddleware<NextApiRequest, NextApiResponse>({
    target: process.env.BACKEND_URL,
    pathRewrite: {
        '^/api/internal': '',
    },
}) as any;

function handler(req: NextApiRequest, res: NextApiResponse) {
    return proxy(req, res, (err) => {
        if (err) {
            console.log(err);
        }

        return res;
    });
}

export {
    handler as GET,
    handler as POST,
};

Client call:

const users = await fetch('/api/internal/users');

Expected behavior (be clear and concise)

Handle proxied requests via Next 13 (App Router)

How is http-proxy-middleware used in your project?

@demo/web@0.1.0 /Users/sergey.samoylov/WebstormProjects/demo/web
└── http-proxy-middleware@3.0.0-beta.1

What http-proxy-middleware configuration are you using?

const proxy = createProxyMiddleware<NextApiRequest, NextApiResponse>({
    target: process.env.BACKEND_URL,
    pathRewrite: {
        '^/api/internal': '',
    },
})

What OS/version and node/version are you seeing the problem?

System:
    OS: macOS 13.3
    CPU: (10) arm64 Apple M1 Pro
    Memory: 130.45 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 16.10.0 - ~/.nvm/versions/node/v16.10.0/bin/node
    Yarn: 1.22.17 - ~/.nvm/versions/node/v16.10.0/bin/yarn
    npm: 7.24.0 - ~/.nvm/versions/node/v16.10.0/bin/npm
    pnpm: 6.35.1 - ~/.nvm/versions/node/v16.10.0/bin/pnpm
  Managers:
    Homebrew: 4.1.4 - /opt/homebrew/bin/brew
    pip3: 23.1 - /Library/Frameworks/Python.framework/Versions/3.10/bin/pip3
    RubyGems: 3.0.3.1 - /usr/bin/gem
  Utilities:
    Make: 3.81 - /usr/bin/make
    GCC: 14.0.3 - /usr/bin/gcc
    Git: 2.39.2 - /usr/bin/git
    Clang: 14.0.3 - /usr/bin/clang
    Curl: 7.87.0 - /usr/bin/curl
  Servers:
    Apache: 2.4.54 - /usr/sbin/apachectl
  Virtualization:
    Docker: 20.10.12 - /usr/local/bin/docker
  IDEs:
    Vim: 9.0 - /usr/bin/vim
    WebStorm: 2021.3.3
    Xcode: /undefined - /usr/bin/xcodebuild
  Languages:
    Bash: 3.2.57 - /bin/bash
    Go: 1.20.3 - /usr/local/go/bin/go
    Perl: 5.30.3 - /usr/bin/perl
    Protoc: 3.21.12 - /opt/homebrew/bin/protoc
    Python3: 3.10.11 - /Library/Frameworks/Python.framework/Versions/3.10/bin/python3
    Ruby: 2.6.10 - /usr/bin/ruby
  Databases:
    MongoDB: 5.0.6 - /opt/homebrew/bin/mongo
    PostgreSQL: 14.9 - /opt/homebrew/bin/postgres
    SQLite: 3.41.2 - /opt/local/bin/sqlite3
  Browsers:
    Chrome: 116.0.5845.140
    Safari: 16.4

[gciluffo]

Same issue here. Had to work around by creating a /pages/api directory adjacent to my app directory in order to get api proxies working.

[jtomaszewski]

I've tried handcrafting it but also failed.

I created app/[...all]/router.ts file with following contents:

import httpProxy from "http-proxy";

export async function GET(request: Request) {
  const proxy: httpProxy = httpProxy.createProxy();
  const response = new Response();

  return new Promise((resolve, reject) => {
    proxy
      .once("proxyRes", resolve)
      .once("error", reject)
      .web(request, response, {
        target: "https://napiachu.pl",
        secure: false,
        changeOrigin: true,
        autoRewrite: true,
        cookieDomainRewrite: "",
      });
  });
}

But it just doesn't work, it raises TypeError: req.on is not a function error.

That's probably because the interface of request & response object is now completely different in app router (request is a node fetch "request" object, not a IncomingMessage class object coming from node http library; and response is simply not existing).

So http-proxy nor http-proxy-middleware can't be used "as is", unless we find some way how we can make it work on top of the new request & response interfaces.

[liambowers]

If you're about to add a 'I have this issue too, +1' kind of comment, I'd suggest giving the first post a thumbs-up which communicates the same and doesn't spam subscribed users unnecessarily.

[karbica]

Same. I wish the route segment config, e.g. const runtime = 'nodejs'; (the default btw), would actually pass the supported request and response interfaces. Instead we get the interfaces that would run on the edge and inside the browser which are incompatible with other third-party proxy implementations.

[KakkoiDev]

I've tried handcrafting it but also failed.

I created app/[...all]/router.ts file with following contents:

import httpProxy from "http-proxy";

export async function GET(request: Request) {
  const proxy: httpProxy = httpProxy.createProxy();
  const response = new Response();

  return new Promise((resolve, reject) => {
    proxy
      .once("proxyRes", resolve)
      .once("error", reject)
      .web(request, response, {
        target: "https://napiachu.pl",
        secure: false,
        changeOrigin: true,
        autoRewrite: true,
        cookieDomainRewrite: "",
      });
  });
}

But it just doesn't work, it raises TypeError: req.on is not a function error.

That's probably because the interface of request & response object is now completely different in app router (request is a node fetch "request" object, not a IncomingMessage class object coming from node http library; and response is simply not existing).

So http-proxy nor http-proxy-middleware can't be used "as is", unless we find some way how we can make it work on top of the new request & response interfaces.

After trying for a while I was still getting the TypeError: req.on is not a function error. So I finally dropped http-proxy-middleware in favor of a more "native" NextJS solution: with a middleware and rewrites.

The logic is as follow: Every time a request starting with /api is made, the middleware will update it as needed and then the rewrites will proxy it to the desired destination.

middleware.ts

// imports...

export async function middleware(request: NextRequest) {
  // your other middleware actions...

  if (/^\/api/.test(path)) { // if sending a request to /api/...
    const newResponse = NextResponse.next(); // prepare a new response

    // modify your response if needed
    const bearerToken = await getBearerToken();
    newResponse.headers.set("Authorization", "Bearer " + bearerToken);
    // ...

    return newResponse; // return the modified response
  }
}

next.config.js

module.exports = {
  // your other config...
  async rewrites() {
    return [
      {
        source: "/api/:path*", // get everything after /api/
        destination: `${process.env.NEXT_PUBLIC_API_URL}/:path*`, // send it to your API
      },
    ];
  },
}

For more information:

• NextJS Middleware: https://nextjs.org/docs/pages/building-your-application/routing/middleware
• NextJS Rewrites: https://nextjs.org/docs/pages/api-reference/next-config-js/rewrites