Can't get a Lambda function to send back information - ios

Question

I just got my first Lambda function written, but it does not work at this point.
I tried a number of variations in the code; partly following what I could think of and partly following what I could come across on the net; but all failed.
I want the Lambda function to listUsers in a UserPool and get an email for a given sub passed as parameter.
Here is the Swift function making the call to the Lambda function:
func getLambdaInfo() {
let lambdaInvoker = AWSLambdaInvoker.default(),
jsonObject:[String: Any] = ["sub" : "MY-USER-SUB"]
lambdaInvoker.invokeFunction("myLambdaFunc", jsonObject: jsonObject)
.continueWith(block: {
(task:AWSTask<AnyObject>) -> Any? in
if( task.error != nil) {
print("Error: \(task.error!)")
return nil
}
print("\(#function) ---- WE ARE HERE!!!!")
// Handle response in task.result:
if let JSONDictionary = task.result as? NSDictionary {
print("Result: \(JSONDictionary)")
}
return nil
})
}
Here is the Lambda function:
var AWS = require('aws-sdk/dist/aws-sdk-react-native');
exports.handler = async (event,context) => {
var params = {
UserPoolId: 'MY-POOL-ID',
AttributesToGet: ['email'],
Limit: '2'
};
var cognitoidentityserviceprovider = new AWS.CognitoIdentityServiceProvider();
cognitoidentityserviceprovider.listUsers(params, function(err, data) {
if (err) console.log(err, err.stack); // an error occurred
else console.log(data); // successful response
// How can I get this data sent in the response is probably the issue ??
});
const response = {
inBound: event.sub,
statusCode: 200,
body: JSON.stringify('Hello from Lambda!')
};
return response;
}
Here is what can be seen in the Xcode debugging console:
getLambdaInfo() ---- WE ARE HERE!!!!
Result: {
body = "\"Hello from Lambda!\"";
inBound = "MY-USER-SUB";
statusCode = 200;
}
I hope someone with more AWSLambda than me will be able to give me some hints concerning the changes I need to make in my code to get the result (email address) I want (into my Swift getLambdaInfo()).

Answer 1

You need to move your return statement in the callback of listUsers:
cognitoidentityserviceprovider.listUsers(params, function(err, data) {
if (err) {
console.log(err, err.stack); // an error occurred
// return a 500 error ?
}
else {
console.log(data);
const response = {
inBound: event.sub,
statusCode: 200,
body: JSON.stringify(data)
}
return response;
}
});
Since you're using the async pattern you can also do:
try {
const data = await cognitoidentityserviceprovider.listUsers(params).promise() // note the await and .promise() here
const response = {
inBound: event.sub,
statusCode: 200,
body: JSON.stringify(data)
}
return response;
} catch (err) {
// do something with err
}
Otherwise your Lambda function returns before your callback gets executed (async nature of JavaScript).