Execute js script to update requestBody before redirect

I am configuring à nginx location but I need to run a script (njs) that update requestBody before redirection :

This my conf but when i deploy it still redirect without update requestBody or return error

Parent nginx.conf:

     // .....
     js_import checkScript from  /etc/nginx/js/scripts/checkScript.js;
     // ....

In checkScript.js :

export default {
    rights
}

function rights(r) {
    const body = JSON.parse(r.requestBody);
    if (body.isAdmin) {
        body.rights = ['ADMIN'];
        r.requestBody = JSON.stringify(body);
    } else {
        r.return(403, 'Not admin');
    }
}

products.http-service.conf :

location /api/data/products/new {
    set $gateway_role "dev.yumStore";
    set $gateway_realm "yumStore";

    auth_request /_tokenExchange;

    # check rights and update body
    js_content checkScript.rights;

    proxy_set_header "Authorization" $gateway_auth_header;

    # redirection
    proxy_pass $OUTGATEWAY/api/data/products/new;
}

Thanks for help!!

You are updating a local copy of the JSON document in your function.

I don't know if this is allowed, but you can try:

function rights(r) {
    const body = JSON.parse(r.requestBody);
    if (body.isAdmin) {
        body.rights = ['ADMIN']
        r.requestBody = JSON.stringify(body); // I don't know if nginx JS allows overwriting the requestBody...
    } else {
        r.return(403, 'Not admin');
    }
}

I hope you have proper authentication for your admin part in addition to this, since this approach is really straightforward to bypass.

Say you send the body detrevni to nginx, a njs module wich inverts the string into inverted, proxy_pass to an upstream server which will respond with echoing: inverted.

The following config works for the test above. Hope it helps.

default.conf:

js_import main from invert.js;

server {
    
    location /ping {
        return 200 'pong';
    }

    location / {
        js_content main.invert;
    }

    location /api {
        proxy_pass http://host.docker.internal:5015;
    }
}

invert.js

async function invert(r) {
  let body = r.requestText;
  let inverted = body.split("").reverse().join("");
  let res = await r.subrequest("/api", { body: inverted });
  r.return(res.status, res.responseBody);
}

export default { invert };

api

const server = new Server(5015, async (request, response) => {
  const incoming = await payload(request);
  const answer = `echoing: ${incoming}`;
  console.log("answering with", answer);
  response.writeHead(200, { "content-type": "text/plain" });
  response.write(answer);
  response.end();
});

The code can be found here: https://github.com/ericminio/learning-nginx/tree/master/njs-modify-body