Get MQTT Topic name coming from AWS IOT CORE to AWS Lambda .Net Core

Question

i need an help. So i need to get from AWS Lambda the topic name subscribed (triggered) from AWS IOT CORE. So this is my code of lambda:

        public string FunctionHandler(Gps message, ILambdaContext context)
    { 
        LambdaLogger.Log("STRING MESSAGE DT: " + message.dt);
        LambdaLogger.Log("STRING MESSAGE LN: " + message.ln);
        LambdaLogger.Log("STRING MESSAGE LT: " + message.lt);
        LambdaLogger.Log("input context: " + context.FunctionName);
        LambdaLogger.Log("input context: " + context.Identity);
        LambdaLogger.Log("input context: " + context.InvokedFunctionArn);
        LambdaLogger.Log("input context: " + context.FunctionName);
        LambdaLogger.Log("input context: " + context.AwsRequestId);
        LambdaLogger.Log("input context: " + context.ClientContext);
        LambdaLogger.Log("input context: " + context.Logger);
        LambdaLogger.Log("input context: " + context.LogStreamName);
        return JsonConvert.SerializeObject(gpsList);
    }

i saw in cloud watch, i received correctly the payload data from MQTT and triggered correctrly. So this is my topic:

AWS/#

this is my payload (geolocations object json) publish on AWS/Test

{
        "dt": "2020-02-26 18:03:30",
        "lt": "xxx.xxx",
        "ln": "yyy.yyy"
}

My aws iot core rule:

SELECT *, topic() as Topic FROM 'AWS/#'

this is my logs from AWS CloudWatch

2021-04-20T09:26:48.457+02:00   STRING MESSAGE DT: 2020-02-26 18:03:30

2021-04-20T09:26:48.473+02:00   STRING MESSAGE LN: xxx.xxx

2021-04-20T09:26:48.473+02:00   STRING MESSAGE LT: yyy.yyy

As you can see i received correctly all data but, i need to read the name of topic. I need to read in this case AWS/Test

I need because the topic will contain basic info like serials of machines, for example 'AWS/xyz'. How can i read the topic name and read 'xyz' from publish MQTT? i need to get Topic name in AWS Lambda. I can't insert the serial machine into payload, but only on the naming of publish topic.

cementblocks cementblocks · Accepted Answer · 2021-04-20T14:54:05

You need to add a .Topic attribute to your Gps class. The event the lambda receives looks like this:

{
  "dt": "2020-02-26 18:03:30",
  "lt": "xxx.xxx",
  "ln": "yyy.yyy"
  "Topic: "your topic here"
}

Get MQTT Topic name coming from AWS IOT CORE to AWS Lambda .Net Core

1 Answers