read POST data from client request

[fsallstrom]

trafficstars

Hi, I have created a proxy server between my client device and server that I use to re-format the server response before it hits the client device. I have used the http-proxy successfully.

Now, I would like to add some logging to the proxy server so that I can see what POST data is sent from the client and has tried this:

proxy.on('proxyReq', function(proxyReq, req, res, options) {
	console.log('incoming client request');
	console.log(req);
}); 

as well as this:

proxy.on('proxyReq', function(proxyReq, req, res, options) {
	console.log('incoming client request');
	console.log(options);
});

without success. Perhaps I have completely misunderstood the concept. Where can I get access to the POST data from the client request? Thank you in advance!

[Sebaci]

req.body may be what you are looking for.

[fsallstrom]

req.body may be what you are looking for.

Thanks, I tried this:

proxy.on('proxyReq', function(proxyReq, req, res, options) {
	console.log(req.body);
});

and get "undefined" in the console

[jsmylnycky]

You need to use a body parsing middleware to populate req.body. It isn't a standard property.

Assuming you're using Express, see: http://expressjs.com/en/resources/middleware/body-parser.html

[fsallstrom]

You need to use a body parsing middleware to populate req.body. It isn't a standard property.

Assuming you're using Express, see: http://expressjs.com/en/resources/middleware/body-parser.html

Thank you for responding. I am not at all familiar with express and what it does. I'm pretty new to node in general and have used http-proxy to create a simple web proxy for doing some modifications of the target server's response. My entire code here:

var httpProxy = require('http-proxy');
const port = process.env.PORT;

var proxy = httpProxy.createServer({
 
  target: 'https://<my_target_hostname>',
  secure: false,
  followRedirects: true,
  autoRewrite: true,
  changeOrigin: true,
  selfHandleResponse: true
}).listen(port, () => {
  console.log(`Server running at port ${port}`)
 });
 
proxy.on('proxyReq', function(proxyReq, req, res, options) {
	console.log('incoming request: ', req.body); //this doesn't work: console output is undefined
});
 
proxy.on('proxyRes', function (proxyRes, req, res) {
        var body = '';
	var response = '';
	proxyRes.on('data', function (chunk) {
            body += chunk;
        });
        proxyRes.on('end', function () {
		response = JSON.parse(body);
		console.log(response);
		res.end(JSON.stringify({SessionID : response}));
        });
});  

Basically there are two things I want to add to my proxy-server; first I want to be able to log the request.body (at least parts of it) and second, I would like to change the reponseCode in the server response before I send it back to the client. The target server always sends back responseCode 200 even though the request could not be served properly.

[fsallstrom]

setting the response responseCode was pretty easy, using writeHead

res.writeHead(401);
res.end(...)

[jsmylnycky]

You still need to use a library capable of parsing the body of a request. Look into using that module on its own if you're not using Express, otherwise there are probably numerous other options out there that do similar things.

[fsallstrom]

Thank you. I think it's a bit over my head. I solved it by having the client send the data I needed to monitor in a customer header, and used proxyReq.getHeader() to fetch it.

[Sebaci]

@fsallstrom You can also take inspiration from this example:

https://github.com/http-party/node-http-proxy/blob/master/examples/middleware/bodyDecoder-middleware.js

[gh-amistry]

Hey, I had a similar issue today. Using your code above for reference:

console.log(response);

Did this return anything? For me it does; I can see all the expected data from the POST.

The problem I was having was that the data would never get sent back to the original client. Using your code above again as an example: res.end(JSON.stringify({SessionID : response})); this would not return and there wouldn't be any error.

What I tried was calling res.write with some non-empty value just before the response, and this works:

res.write('x');
res.write()res.end(JSON.stringify({SessionID : response}));

Unfortunately, the response that the client gets has a character that needs to be stripped.

Is this by design or is this a bug? Thanks!

[jeanffc]

I had the same problem.

I am using express and body-parser to JSON.

I fixed adding this restream parsed body before proxying:

//restream parsed body before proxying
proxy.on('proxyReq', function(proxyReq, req, res, options) {
  if (!req.body || !Object.keys(req.body).length) {
    return;
  }

  var contentType = proxyReq.getHeader('Content-Type');
  var bodyData;

  if (contentType === 'application/json') {
    bodyData = JSON.stringify(req.body);
  }

  if (contentType === 'application/x-www-form-urlencoded') {
    bodyData = queryString.stringify(req.body);
  }

  if (bodyData) {
    proxyReq.setHeader('Content-Length', Buffer.byteLength(bodyData));
    proxyReq.write(bodyData);
  }
});

[alijch89]

what if header include form-data and want to parse file before proxy request ?