Dialogflow response with output context crashes PHP/Symfony server - symfony

Question

TL;DR
My PHP/Symfony server crashes when Dialogflow sends a response with output context, but works fine when the response does not have any output context.
Why is that so and how can I prevent my server from crashing ?
Some context
I'm working on a old project made by a colleague who left the company a few months ago.
The project uses Dialogflow and a PHP/Symfony server to create a chatbot.
Back in January, the project worked well, but when I tried to test it last week, I discovered our server had been irremediably removed from the host.
I reuploaded and reinstalled the server code but I cannot be 100% sure that the backup code was exactly the same as the hosted code.
Correct behaviour
I send "hey" to the server
The server transmits the message to Dialogflow
Dialogflow determines that the intent is "Welcome"
Dialogflow sends back "Salutations" to the server
I get the response "Salutations"
Faulty behaviour
I send "help" to the server
The server transmits the message to Dialogflow
Dialogflow determines that the intent is "Help"
Dialogflow sends back "[some long text]" to the server
The server crashes and returns a generic error 500
Same goes for the default fallback intent, if I send a request like "blah blah blah".
The difference
The Welcome intent does not provide output context, nor does it reset the context.
The Help intent does provide output context.
The Fallback intent does not provide output context, but does reset the context.
I verified, if I provide output context with the Welcome intent, the server crashes, and if I remove the output context from the Help intent, everything works fine.
The questions
What is going on with this project ? Why is the output context crashing my server ? How can I fix it ?
I can't just remove the output contexts from the intents, of course.
The code
<?php
namespace AppBundle\Controller;
use Ramsey\Uuid\Uuid;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;
use Google\Cloud\Dialogflow\V2\SessionsClient;
use Google\Cloud\Dialogflow\V2\TextInput;
use Google\Cloud\Dialogflow\V2\QueryInput;
class DefaultController extends Controller
{
/**
* #Route("/messenger", name="homepage")
*
*/
public function indexAction(Request $request)
{
return $this->render('#App/messenger.twig', array());
}
/**
* #param Request $request
*
* #Route("/messenger/call/{intent}", options={"expose"=true}, name="call_assistant")
* #throws \Google\ApiCore\ValidationException
* #throws \Google\ApiCore\ApiException
* #throws \Exception
*/
public function callAssistantAction(Request $request, $intent) {
$sessionDialogFlow = $this->get('session')->get('dialogFlow_session');
if ($sessionDialogFlow === null) {
$sessionDialogFlow = Uuid::uuid4()->toString();
$this->get('session')->set('dialogFlow_session', $sessionDialogFlow);
}
$sessionClient = new SessionsClient(array(
'credentials' => realpath($this->getParameter('kernel.root_dir'). "/../web/authentDialogFlow.json")
));
$session = $sessionClient->sessionName("<my session name>", $sessionDialogFlow);
$textInput = new TextInput();
$textInput->setText($intent);
$textInput->setLanguageCode('fr-FR');
$queryInput = new QueryInput();
$queryInput->setText($textInput);
$response = $sessionClient->detectIntent($session, $queryInput); // <- this line is where the crash happens
$queryResult = $response->getQueryResult();
$fulfillmentText = $queryResult->getFulfillmentText();
return new JsonResponse(array("response" => $fulfillmentText));
}
}
The Welcome dialogflow output
{
"queryText": "hey",
"action": "input.welcome",
"parameters": {},
"fulfillmentText": "Salutations !",
"fulfillmentMessages": [
{
"text": {
"text": [
"Salutations !"
]
},
"lang": "fr"
}
],
"intent": {
"id": "<id>",
"displayName": "Default Welcome Intent",
"priority": 500000,
"events": [
"WELCOME"
],
"action": "input.welcome",
"messages": [
{
"text": {
"text": [
"Hi! How are you doing?",
"Hello! How can I help you?",
"Good day! What can I do for you today?",
"Greetings! How can I assist?"
]
},
"lang": "en"
},
{
"text": {
"text": [
"Salut !",
"Bonjour !",
"Salutations !",
"Bienvenue !"
]
},
"lang": "fr"
}
]
},
"intentDetectionConfidence": 1,
"languageCode": "fr",
"slotfillingMetadata": {
"allRequiredParamsPresent": true
},
"id": "<id>",
"sessionId": "<id>",
"timestamp": "2019-07-15T07:41:28.778Z",
"source": "agent",
"webhookStatus": {
"webhookEnabledForAgent": true
},
"agentEnvironmentId": {
"agentId": "<id>",
"cloudProjectId": "<id>"
}
}
The Help dialogflow output
{
"queryText": "aide",
"parameters": {},
"fulfillmentText": "<long text>",
"fulfillmentMessages": [
{
"text": {
"text": [
"<long text>"
]
},
"lang": "fr"
}
],
"intent": {
"id": "<id>",
"displayName": "Help",
"priority": 500000,
"messages": [
{
"text": {
"text": [
"<long text>"
]
},
"lang": "fr"
}
]
},
"intentDetectionConfidence": 1,
"languageCode": "fr",
"slotfillingMetadata": {
"allRequiredParamsPresent": true
},
"id": "<id>",
"sessionId": "<id>",
"timestamp": "2019-07-15T13:05:25.255Z",
"source": "agent",
"webhookStatus": {
"webhookEnabledForAgent": true
},
"agentEnvironmentId": {
"agentId": "<id>",
"cloudProjectId": "<id>"
}
}
Feel free to ask for additional information.

Answer 1

After days of gloom, it turned out my server was missing PHP extension bcmath needed by google/protobuf. I enabled it in my php.ini and everything worked fine.
You can find a bit more information on the Github issue : https://github.com/googleapis/google-cloud-php/issues/2120