Subrequests chaining [http/subrequests_chaining]

Chaining subrequests allows us to use the output of one subrequest as the input to another.

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

EXAMPLE='http/subrequests_chaining'
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/start -H 'Authorization: Bearer secret'
Token is 42

curl http://localhost/start
SyntaxError: Unexpected token at position 0

curl http://localhost/start -H 'Authorization: Bearer secre'
Error: token is not available

docker stop njs_example

Code Snippets

Notice how this config uses location blocks to define the target of each subrequest.

nginx.conf

...

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

  js_import utils.js;
  js_import main from http/subrequests_chaining.js;

  server {
        listen 80;

        location / {
            js_content main.process;
        }

        location = /auth {
            internal;
            proxy_pass http://localhost:8080;
        }

        location = /backend {
            internal;
            proxy_pass http://localhost:8090;
        }
  }

  ...

    server {
          listen 8080;

          location / {
              js_content main.authenticate;
          }
    }

    server {
          listen 8090;

          location / {
              return 200 "Token is $arg_token";
          }

}

This njs code retrieves a token from the “/auth” location and then passes the token to a second subrequest of the “/backend” location.

subrequests_chaining.js

  function process(r) {
      r.subrequest('/auth')
          .then(reply => JSON.parse(reply.responseBody))
          .then(response => {
              if (!response['token']) {
                  throw new Error("token is not available");
              }
              return response['token'];
          })
      .then(token => {
          r.subrequest('/backend', `token=${token}`)
              .then(reply => r.return(reply.status, reply.responseBody));
      })
      .catch(e => r.return(500, e));
  }

  function authenticate(r) {
      if (r.headersIn.Authorization.slice(7) === 'secret') {
          r.return(200, JSON.stringify({status: "OK", token:42}));
          return;
      }

      r.return(403, JSON.stringify({status: "INVALID"}));
  }

  export default {process, authenticate}