PHP Slim framework ErrorHandler - send exception to client - slim

Question

I implemented ErrorHandler in my Slim Framework REST API:
$container['errorHandler'] = function ($c) {
return function (ServerRequestInterface $request, Response $response, $exception) use ($c) {
$data = [
'message' => $exception->getMessage()
];
return $c->get('response')->withStatus(500)
->withHeader('Content-Type', 'application/json')
->write(json_encode($data));
};
};
I try to create error:
public function test(ServerRequestInterface $request, Response $response){
$email = null;
$arr = [1,2];
$x = $arr[3]; //Undefined array key 3
}
I see the error in the Postman correctly (Status 500, {message: Undefined array key 3}, but in Developer tools in browser (Response tab) is only "Failed to load response data: No data found for resource with gived identifier".
In JS is this error:
{"headers":{"normalizedNames":{},"lazyUpdate":null,"headers":{}},"status":0,"statusText":"Unknown Error","url":"http://localhost:8080/auth/login","ok":false,"name":"HttpErrorResponse","message":"Http failure response for http://localhost:8080/auth/login: 0 Unknown Error","error":{"isTrusted":true}}
When I send error response from test method:
public function test(ServerRequestInterface $request, Response $response){
return $response->withStatus(500)
->withHeader('Content-Type', 'application/json')
->write("ERROR");
}
in JS is correct exception object, and I see response in Developer tools:
{"headers":{"normalizedNames":{},"lazyUpdate":null},"status":500,"statusText":"Internal Server Error","url":"http://localhost:8080/auth/login","ok":false,"name":"HttpErrorResponse","message":"Http failure response for http://localhost:8080/auth/login: 500 Internal Server Error","error":"ERROR"}
what could be the problem? How to send error from errorHandler correctly?
Thanks for advices

Answer 1

The PSR-7 headers are immutable, but the HTTP body methods are not immutable.
To fix it try this:
$response = $response
->withStatus(500)
->withHeader('Content-Type', 'application/json');
$response->getBody()->write(json_encode($data)));
return $response;