Cannot proxy after parsing body

[connelhooley]

I cannot re-send a proxied request's body after I have parsed it.

Using this recipe, this comment and this comment I have written the following example:

import express from 'express';
import proxy from 'http-proxy-middleware';
import bodyParser from 'body-parser'

const app = express();
app.use(bodyParser.json());
app.post('*', proxy({
    target: 'http://target.here.com',
    secure: false,
    onProxyReq: (proxyReq, req) => {
        if (req.body) {
            const bodyData = JSON.stringify(req.body);
            proxyReq.setHeader('Content-Type','application/json');
            proxyReq.setHeader('Content-Length', Buffer.byteLength(bodyData));
            proxyReq.write(bodyData);
        }
    }
}));
app.listen(2001, () => console.log('Listening'));

I get an error when trying to set the first header on the proxyReq saying: Cannot set headers after they are sent to the client.

If that is the case how does the recipe work?

[connelhooley]

Looks related to:
http-party/node-http-proxy#1279

[SBRK]

+1 got the same issue. Moving the middlewares before body.json works

[connelhooley]

+1 got the same issue. Moving the middlewares before body.json works

Yes that's correct. I need to parse the body to know if I need to proxy the request though.

[windix]

If need to parse the body before proxy, I have followed suggestion from this issue: #177 (comment)

[taozhi8833998]

same issue

[ThalesMatoso]

+1

[risu-p]

+1

[stuartZhang]

This is my solution: https://github.com/stuartZhang/coexist-parser-proxy

[chimurai]

fixed in #492

[phoenixstudiodz]

The solutions proposed here worked fine, but after adding an agent (sock5 SocksProxyAgent from socks-proxy-agent) I started getting Can't set headers after they are sent to the client.
I fixed that by overriding verify in the bodyParser.

//
const bodyParser = require('body-parser') 
const { Readable } = require('stream');
//
app.use(bodyParser.json({
  // verify function has access to buff that contains the stream
  // create a new readable stream and save it to streamBody
  verify: (req, res, buf, encoding) => {
  const readableStream = Readable.from(buf);
  req.streamBody = readableStream
 }
}));
 // Param "buffer" accept a stream if the original one was consumed
app.all("*", (req, res) => proxy.web(req, res, {
 target: "target-here",
 buffer: req.streamBody
});