Empty Body on POST Request in Guzzle6/PSR7 - php

Question

I use Guzzle6 in the PSR7 flavor because it integrates nicely with Hawk authentication. Now, I face problems adding a body to the request.
private function makeApiRequest(Instructor $instructor): ResponseInterface
{
$startDate = (new CarbonImmutable('00:00:00'))->toIso8601ZuluString();
$endDate = (new CarbonImmutable('00:00:00'))->addMonths(6)->toIso8601ZuluString();
$instructorEmail = $instructor->getEmail();
$body = [
'skip' => 0,
'limit' => 0,
'filter' => [
'assignedTo:user._id' => ['email' => $instructorEmail],
'start' => ['$gte' => $startDate],
'end' => ['$lte' => $endDate],
],
'relations' => ['reasonId']
];
$request = $this->messageFactory->createRequest(
'POST',
'https://app.absence.io/api/v2/absences',
[
'content_type' => 'application/json'
],
json_encode($body)
);
$authentication = new HawkAuthentication();
$request = $authentication->authenticate($request);
return $this->client->sendRequest($request);
}
When I var_dump the $request variable, I see no body inside the request. This is backed by the fact that the API responds as if no body was sent. I cross-checked this in Postman. As you can see, the body specifies filters and pagination, so it is easy to see that the results I get are actually not filtered.
The same request in Postman (with body) works flawlessly.
As the parameter be can of type StreamInterface I created a stream instead and passed the body to it. Didn't work either.

Answer 1

Simple JSON requests can be created without using json_encode()... see the documentation.
use GuzzleHttp\Client;
$client = new Client([
'base_uri' => 'https://app.absence.io/api/v2',
'timeout' => 2.0
]);
$response = $client->request('POST', '/absences', ['json' => $body]);

Answer 2

Found the problem, actually my POST body is NOT empty. It just turns out that dumping the Request will not hint anything about the actual body being enclosed in the message.
I can recommend anyone having similar problems to use http://httpbin.org/#/HTTP_Methods/post_post to debug the POST body.
Finally, the problem was that my content_type header spelling was wrong as the server expects a header Content-Type. Because of this, the JSON data was sent as form data.