How to modify req.body?

[Doun72]

I try to modify the parameters (password) from proxyOnRequest before sending them the web server.
In my index.js, I have the following "redbird" function:
reverseProxy.register("node:5470", "web:4000", {ssl:false, useTargetHostHeader: true});

Then I call this function:
reverseProxy.proxy.on('proxyReq', changetohash.onRequest());

Inside the "changetohash" function, I want to modify the received password and send it again as parameter for the web server.

The only way to retrieve the parameter is to use this function (request.on):

export function onRequest (options) {
return function hashOnRequest(proxyRequest, request, response, options) {
if (((proxyRequest.path == "/signup") || (proxyRequest.path == "/login")) && (request.method == 'POST')) {
// Make any needed POST parameter changes
let body = '';
request.on('data', (chunk) => {
body += chunk;
}).on('end', () => {
//I try to modify the request header here
});
....

but when I wanted to modify the request header:
request.setHeader( 'content-length', body.length );

I obtain a error: "the request is already closed"
The 'content-type' is 'application/x-www-form-urlencoded'

Any ideas how to retrieve the body of my request? I tried directly request.body but it didn't work.

Thanks for your help.

[amalhotragannett]

we need to wait till the request has been finished.

function waitTillRequestEnds(request) {
 // you can change the logic to what you want on the request fields method, path, ....
  if (request.method === 'POST') {
    return new Promise((resolve) => {
      const body = [];
      request.on('data', (chunk) => {
        body.push(chunk);
      });
      request.on('end', () => {
        resolve(Buffer.concat(body).toString());
      });
    });
  } else {
    return;
  }
};

Now we will listen to the event proxyReq on the proxy server.

proxy.on('proxyReq', async (proxyReq, request, res, options) => {
  const requestBody = await waitTillRequestEnds(request); // will return the request body
  const newBody = requestBody.concat(' ', 'bar'); // changing the body
  proxyReq.setHeader('x-header', 'my-custom-header'); // changing the header
  proxyReq.write(newBody); // restream body before proxying 
});

[Doun72]

Thanks for your help. I tried what you proposed but I had the following error message on this line(proxyRequest.setHeader('x-header','my-custom-header');):
Cannot set headers after they are sent to the client
at ClientRequest.setHeader (_http_outgoing.js:541:11)
at ProxyServer.hashOnRequest

[amalhotragannett]

Are you behind a corporate firewall? There is an open issue with node-http-proxy which is the backend for redbird.

There is a workaround mentioned on the issue. Check if that helps you resolve the issue.