How to manipulate reponses without content-length

[diegogonzalez]

I'm trying to manipulate reponses, and adding headers. I just realized, thanks to this page that it the response doesn't contain the content-length header the onProxyRes will not receive the response in the buffer. I can't manipulate the headers neither.

Is it possible to achieve this?

[chimurai]

Thanks for reaching out.
Do you have a reproducible example?

[diegogonzalez]

Hey @chimurai thanks for answering. Yes here is the full code, accesing to localhost you can reproduce the issue.

const { createProxyMiddleware, responseInterceptor } = require('http-proxy-middleware');
const http = require('http');
const connect = require('connect');


const proxy = createProxyMiddleware({
    target: "http://www.notion.so" ,

    changeOrigin: true,
    /**
     * IMPORTANT: avoid res.end being called automatically
     **/
    selfHandleResponse: true, 

    /**
     * Intercept response and replace 'Hello' with 'Goodbye'
     **/
    onProxyRes: responseInterceptor(async (responseBuffer, proxyRes, req, res) => {
        res.setHeader("custom-header", "header-value");
        const response = responseBuffer.toString('utf8'); // convert buffer to string
        return response.replaceAll('Hello', 'GoodBye'); // manipulate response and return the result
    }),
});


const app = connect();

/**
 * Add the proxy to connect
 */
app.use('/', proxy);

const server = http.createServer(app).listen(80);

I tried it with several versions and with all the same thing happens to me, but just in case these are the versions that I'm using

    "connect": "^3.7.0",
    "http-proxy-middleware": "^2.0.6"
```

[chimurai]

You've set your target with the http: protocol
This causes a 302 redirect from http://localhost to https://www.notion.so

After changing the target to https: I'm able to modify the response:

-    target: "http://www.notion.so" ,
+    target: "https://www.notion.so" ,

Alternatively you can add the option to handle the redirects:

  target: "http://www.notion.so" ,
+ followRedirects: true,

Original:

Manipulated response:

Full example:

const { createProxyMiddleware, responseInterceptor } = require('http-proxy-middleware');
const http = require('http');
const connect = require('connect');


const proxy = createProxyMiddleware({
    target: "https://www.notion.so" ,

    changeOrigin: true,
    /**
     * IMPORTANT: avoid res.end being called automatically
     **/
    selfHandleResponse: true, 

    /**
     * Intercept response and replace 'Hello' with 'Goodbye'
     **/
    onProxyRes: responseInterceptor(async (responseBuffer, proxyRes, req, res) => {

        res.setHeader("custom-header", "header-value");
        const response = responseBuffer.toString('utf8'); // convert buffer to string
        return response.replaceAll('workspace', 'world').replaceAll('team', 'human'); // manipulate response and return the result
    }),
});


const app = connect();

/**
 * Add the proxy to connect
 */
app.use('/', proxy);

const server = http.createServer(app).listen(3000);

[diegogonzalez]

Ahh ok, sorry.. I thought that the target was sending the content in the response.
Thank you very much for your responses!