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Dart AppSync Subscription
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var query = { | |
'operationName': 'OnNewPets', | |
'query': '''subscription OnNewPets { | |
onCreatePet { | |
id | |
name | |
description | |
} | |
}''' | |
}; | |
var _endpoint = 'https://yourendpoint.appsync-api.us-east-1.amazonaws.com/graphql' | |
try { | |
http.post( | |
'$_endpoint', | |
headers: { | |
'Authorization': _session.getAccessToken().getJwtToken(), //_session comes from amazon_cognito_identity_dart package | |
'Content-Type': 'application/json', | |
}, | |
body: json.encode(query), | |
) | |
.then((data) { | |
Map<String, dynamic> response = | |
jsonDecode(data.body) as Map<String, dynamic>; | |
mqtt.MqttClient _client; | |
mqtt.MqttConnectionState connectionState; | |
_client = mqtt.MqttClient( | |
response['extensions']['subscription']['mqttConnections'][0]['url'] | |
.toString(), | |
response['extensions']['subscription']['mqttConnections'][0]['client'] | |
.toString()); | |
_client.logging(on: true); | |
_client.keepAlivePeriod = 300; | |
_client.useWebSocket = true; | |
_client.onDisconnected = () => print("Disconnected"); | |
_client.onConnected = () => print("Connected"); | |
_client.onSubscribed = (value) => print(value); | |
_client.port = 443; | |
try { | |
_client.connect().then((data) { | |
if (_client.connectionStatus.state == MqttConnectionState.connected) { | |
print('CONNECTED!'); | |
try { | |
_client.subscribe( | |
response['extensions']['subscription']['mqttConnections'][0] | |
['topics'][0] | |
.toString(), | |
MqttQos.atMostOnce); | |
_client.updates | |
.listen((List<MqttReceivedMessage<MqttMessage>> c) { | |
final MqttPublishMessage recMess = | |
c[0].payload as MqttPublishMessage; | |
final String pt = MqttPublishPayload.bytesToStringAsString( | |
recMess.payload.message); | |
print( | |
'EXAMPLE::Change notification:: topic is <${c[0].topic}>, payload is <-- $pt -->'); | |
print(''); | |
}); | |
_client.published.listen((MqttPublishMessage message) { | |
print( | |
'EXAMPLE::Published notification:: topic is ${message.variableHeader.topicName}, with Qos ${message.header.qos}'); | |
}); | |
} catch (error) { | |
print(error); | |
} | |
} | |
print(data); | |
}); | |
} on Exception catch (e) { | |
print('EXAMPLE::client exception - $e'); | |
_client.disconnect(); | |
} | |
}); | |
} catch (e) { | |
print(e); | |
} |
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I've been using this code for some time, and recently AppSync subscription would randomly stop working for a day. What I found is - sometimes AppSync will maintain sevearal topics, and I would need to subscribe to topic 1, not topic 0 as this code does. This was also the reason it would randomly start working - when the old topic expired, code would start working again.
The solution - we need to grab the topic from "newSubscriptions" and find the right mqqt connection.
Something like this:
`