Using Axios' Proxy Option

Oct 26, 2020

Axios supports a proxy option that lets you define an HTTP proxy for your request. A proxied request is an HTTP request that Axios sends to a different server (the proxy server) than the request is actually meant for. The idea is that the proxy server will do something with the request before sending it to where the request is meant to go.

Below is the basic syntax of how you can proxy a request that is meant for httpbin.org to a proxy server listening on localhost:3000.

const axios = require('axios');
const res = await axios.get('http://httpbin.org/get?answer=42', {
  // `proxy` means the request actually goes to the server listening
  // on localhost:3000, but the request says it is meant for
  // 'http://httpbin.org/get?answer=42'
  proxy: {
    host: 'localhost',
    port: 3000
  }
});
console.log(res.data);

How A Proxied Request Works on the Server

Let's take a look at the technical details of a proxied request. The http-proxy npm package is a popular HTTP proxy. Here's a script that listens on port 3000 and prints any requests before sending them out to their intended destination.

const express = require('express');
const httpProxy = require('http-proxy');

// Create a proxy and listen on port 3000
const proxy = httpProxy.createProxyServer({});
const app = express();
app.get('*', function(req, res) {
  // Prints "Request GET https://httpbin.org/get?answer=42"
  console.log('Request', req.method, req.url);
  proxy.web(req, res, { target: `${req.protocol}://${req.hostname}` });
});
const server = await app.listen(3000);

const axios = require('axios');
const res = await axios.get('http://httpbin.org/get?answer=42', {
  // `proxy` means the request actually goes to the server listening
  // on localhost:3000, but the request says it is meant for
  // 'http://httpbin.org/get?answer=42'
  proxy: {
    host: 'localhost',
    port: 3000
  }
});
console.log(res.data);

Notice that Express reports req.url is an httpbin.org URL! That's what we mean when we say Axios sends the request to a different server than the request is intended for. The URL associated with the request, req.url, is different than the proxy server's URL, and the proxy server is responsible for forwarding the request to req.url.

Proxy servers often do some sort of transformation to the request. For example, a proxy server may set an authorization header so your request doesn't have to.

const proxy = httpProxy.createProxyServer({});
proxy.on('proxyReq', function(proxyReq) {
  proxyReq.setHeader('Authorization', 'my-secret-key');
});

const app = express();
app.get('*', function(req, res) {
  proxy.web(req, res, { target: `${req.protocol}://${req.hostname}` });
});
const server = await app.listen(3000);

Now, if you make the same request with Axios, the proxy server will add the 'Authorization' header for you, and httpbin.org will include it in the response.

const axios = require('axios');
const res = await axios.get('http://httpbin.org/get?answer=42', {
  proxy: {
    host: 'localhost',
    port: 3000
  }
});
console.log(res.data.headers['authorization']); // "my-secret-key"

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