How to send message back to device from Lambda function? - aws-lambda

Question

Is there any way we can send a message to a device from Lambda function which is invoked by Alexa Skill. The message contains some values collected by Lambda function.
So basically I want to do this:
Device ---> Voice command ---> Alexa Skill --(Trigger)--> Lambda function
Lambda function(collect values) ---- message ---> Device
Is there any example in Java?
Thanks for any pointer/help.
-James

Answer 1

Invoke Alexa device from lambda function is a very similar question, with the answer: "it's not possible YET"
I will elaborate. You can send notifications to all users of a skill such as a new feature, however, you cannot send a notification to a specific user that invokes a function.
To send notifications to all users of an Alexa skill who have notifications enabled, see this design.
Reference this thread for more information on the limitations of sending a notification to a specific user.

Answer 2

What you are asking can be done.
First the voice command does not come from a human from your diagram.
A device talks to Alexa. Alexa invokes or triggers Lambda. Lambda function messages device.
The function inside Lambda is http or https. If your device can handle https or TLS encryption then good. But most of the device are small and have limited computing power, so you will end up using http. As of now 2020, AWS allows http, but a year from now it requires you to use https or TLS 1.3 due to federal regulations. But we don't know until it happens.
Below is a sample of Lambda http post in NodeJS. The trigger data comes in request. So you should know what JSON will come in and extract your data from JSON using the if statement.
NodeJS website has good examples for http.
Now your device is the server. It has to anticipate the Lambda request and process it and reply to Lambda if needed.
Now your device talks and receives information.
const http = require('http');
exports.handler = async (request, context) => {
if (request.directive.header.namespace === 'FromAlexaSkill') {
httpost("This is your data to device", "192.168.1.2");
}
//**********************************************
let httpPost =async (postData, servername) => {
let dataString = '';
const response = await new Promise((resolve, reject) => {
const options = {
hostname: servername,
port: 1777,
path: '/dim',
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-urlencoded',
'Content-Length': Buffer.byteLength(postData)
}
};
const req = http.request(options, (res) =>
{
res.setEncoding('utf8');
res.on('data', chunk => {
dataString += chunk;
});
res.on('end', () => {
resolve({
"body":dataString
});
});
});//http.request
req.on('error', (e) => {
console.error("problem with request: "+e.message);
reject({
statusCode: 500,
body: 'Something went wrong!'
});
});
// Write data to request body
req.write(postData);
req.end();
}); //Promise
return response;
};//httpPost
}