Substitute invalid UTF-8 in JSON error renderer output

[iliaal]

json_encode() returns false when any string in the payload contains an invalid UTF-8 sequence, so a JSON error response for an exception whose message or title carries raw binary data (invalid-UTF-8 user input echoed into exception messages is the common path) was emitted as a zero-length body under Content-Type: application/json. Strict API clients then fail to parse the empty body and the actual error information is silently discarded.

This adds JSON_INVALID_UTF8_SUBSTITUTE so invalid byte sequences are replaced with the UTF-8 replacement character instead of failing the whole encode. The renderer output stays valid JSON in all cases.

Reproduction on 4.x before this change:

$renderer = new \Slim\Error\Renderers\JsonErrorRenderer();
$output = $renderer(new \RuntimeException("bad \xB1\x31 bytes"), true);
var_dump(strlen($output)); // int(0)

[coveralls]

coverage: 99.456%. remained the same — iliaal:fix/json-error-renderer-invalid-utf8 into slimphp:4.x

[akrabat]

I changed line 41 of JsonErrorRenderer back to JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES and the test didn't fail.

There's a couple of problems with the test.

First, the false in $output = $renderer->__invoke($exception, false); means that the error details are not rendered, and so only the title ("Slim Application Error") is encoded, so the JSON returned is:

{
    "message": "Slim Application Error"
}

which doesn't include the message we're looking for.

Secondly asserting that the key message exists in the array doesn't test that the invalid UTF-8 is correctly encoded in the JSON.

Can you update the test to prove that the change works?

[iliaal]

displayErrorDetails=false only encoded the title, so the invalid UTF-8 never reached json_encode. I changed the test to pass true and assert the decoded exception message is "Invalid \u{FFFD}1 UTF-8 sequence". That assertion fails if JSON_INVALID_UTF8_SUBSTITUTE is dropped.

[akrabat]

LGTM