[ Question ] How do you manipulate proxy response

Hi, I’m using Express 4,

In normal way, I can do the following

    app.get('/v1/users/:username', function(request, response, next) {
        var username = request.params.username;
        findUserByUsername(username, function(error, user) {
            if (error) return next(error);
            return response.render('user', user);
        });
    });

But how do I execute custom logic if I’m using proxy, let’s say I want to manipulate some of the data before response to the user? Is there a good pattern to do that with this middleware ?

app.use('/api', proxy({target: 'http://www.example.org', changeOrigin: true}));

[cokeknight]

here is my answer,

onProxyRes :function(proxyRes, req, res){
      var _write = res.write;
      var output;
      var body = "";
      proxyRes.on('data', function(data) {
          data = data.toString('utf-8');
          body += data;
      });
      res.write = function (data) {
        try{
          eval("output="+body)
          output = mock.mock(output)
          _write.call(res,JSON.stringify(output));
        } catch (err) {}
      }
    }

add onProxyRes option on the http-proxy-middleware use the data event on the proxyRes to get the output then modify the output in res.write

[mrt123]

My solution:

const zlib = require('zlib');
...
onProxyRes: (proxyRes, req, res) => {
	let originalBody = new Buffer('');
	proxyRes.on('data', function (data) {
		originalBody = Buffer.concat([originalBody, data]);
	});
	proxyRes.on('end', function () {
		const bodyString = zlib.gunzipSync(originalBody).toString('utf8')
		const objectToModify = JSON.parse(bodyString)
		objectToModify.modification = 'Mickey Mouse'
		res.end(JSON.stringify(objectToModify));
	});
},
selfHandleResponse: true . // necessary to avoid res.end being called automatically
...