Nuxt: modify a response from a proxied server using NuxtJS server middleware

Question

I'm using NuxtJS server middleware as a proxy pass as described in this article to proxy incoming requests to an internal service in order to avoid cross domain issues.

const httpProxy = require('http-proxy')
const proxy = httpProxy.createProxyServer()
const API_URL = 'https://api.mydomain.com'

export default function(req, res, next) {
  proxy.web(req, res, {
    target: API_URL
  })
}

How can I analyse the response of the proxied server and potentially modify it at this level?

Answer 1

I've found an example in the http-proxy documentation. To modify the response, selfHandleResponse must be set to true. Here is the example in documentation:

var option = {
  target: target,
  selfHandleResponse : true
};
proxy.on('proxyRes', function (proxyRes, req, res) {
    var body = [];
    proxyRes.on('data', function (chunk) {
        body.push(chunk);
    });
    proxyRes.on('end', function () {
        body = Buffer.concat(body).toString();
        console.log("res from proxied server:", body);
        res.end("my response to cli");
    });
});
proxy.web(req, res, option);

The code below allowed me to handle the proxied answer if the request matches a certain url and just forward (pipe) it otherwise.

proxy.once('proxyRes', function(proxyRes, req, res) {
  if (!req.originalUrl.includes('api/endpoint')) {
    res.writeHead(proxyRes.statusCode) // had to reset header, otherwise always replied proxied answer with HTTP 200
    proxyRes.pipe(res)
  } else {
    // modify response
    let body = []
    proxyRes.on('data', function(chunk) {
      body.push(chunk)
    })
    proxyRes.on('end', function() {
      body = Buffer.concat(body).toString()
      console.log('res from proxied server:', body)
      res.end('my response to cli')
    })
  }
})

Note I add to replace .on() with once() to make it work.