Converting response body characters to lower case [http/response/to_lower_case]

NGINX Javascript now provides a js_body_filter directive to modify the response body before returning it to the client. In this example, we just convert the body text to lower case.

Step 1: Use the following commands to start your NGINX container with this lab’s files:

EXAMPLE='http/response/to_lower_case'
docker run --rm --name njs_example  -v $(pwd)/conf/$EXAMPLE.conf:/etc/nginx/nginx.conf:ro -v $(pwd)/njs/:/etc/nginx/njs/:ro -p 80:80 -d nginx

Step 2: Now let’s use curl to test our NGINX server:

curl http://localhost/
hello world

docker stop njs_example

Code Snippets

This config proxies requests to a simple upstream on port 8080. Responses are passed through the main.to_lower_case method before being returned to the client.

nginx.conf

...

http {
  js_path "/etc/nginx/njs/";

  js_import main from http/response/to_lower_case.js;

  server {
        listen 80;

        location / {
            js_body_filter main.to_lower_case;
            proxy_pass http://localhost:8080;
        }
  }

  server {
        listen 8080;

        location / {
            return 200 'Hello World';
        }
  }
}

This njs code takes the “data” returned by the upstream server and uses the .toLowerCase() method to convert it to lower case. It then constructs a new response using r.sendBuffer() that is sent to the client instead.

to_lower_case.js

  function to_lower_case(r, data, flags) {
      r.sendBuffer(data.toLowerCase(), flags);
  }

  export default {to_lower_case};