HttpFoundation Request POST parameters

Question

From VueJS, I am sending a POST HTTP request to my Drupal 8 controller.

Here is my Controller:

<?php

namespace Drupal\mymodule\Controller;

use Drupal\Core\Controller\ControllerBase;
use Symfony\Component\HttpFoundation\Request;

class ExampleController extends ControllerBase {

  public function doSomething( Request $request) {

    \Drupal::logger('mymodule')->notice($request->getContent());
    \Drupal::logger('mymodule')->notice($request->request->get('message'));

    return [];
  }
}

The first log entry outputs:

@"params":{"message":"hello world","headers":@"Content-Type":"application/json; charset=UTF-8","Access-Control-Allow-Origin":"http://localhost:8080"}

The second log entry fails (it is empty).

What am I doing wrong and how am I supposed to retrieve this message POST parameter?

For completeness, here is the JS POST request:

this.$http.post('http://mydrupal8.url/simple_path', {
  params: {
    'message': 'hello world'
  },
  headers: {
    'Content-Type': 'application/json; charset=UTF-8',
    'Access-Control-Allow-Origin': 'http://localhost:8080',
  }
}).then(response => {
  // response
}, response => {
  // error callback
});

mymodule.routing.yml file:

mymodule.api_example:
  path: 'simple_path'
  defaults:
    _controller: '\Drupal\mymodule\Controller\ExampleController::doSomething'
  methods: [POST]
  requirements:
    _access: 'TRUE'

Answer 1

Apparently with Vue Resource, I need to add emulateJSON:

emulateJSON boolean Send request body as application/x-www-form-urlencoded content type.

this.$http.post('http://mydrupal8.url/simple_path', {
  params: {
    'message': 'hello world'
  },
  headers: {
    'Access-Control-Allow-Origin': 'http://localhost:8080',
  }
}, {
  emulateJSON: true
}).then(response => {

  console.log(response);

}, response => {
  // error callback
});

Now in my D8 backend:

$params = $request->request->get('params');
$message = $params['message'];

And now it works as expected.