When Serialisation goes bad- payload_fields
This is the third in a series of posts about building an HTTP Integration for a The Things Network(TTN) application.
In part 1 & part 2 I had been ignoring the payload_fields property of the Payload class. The documentation indicates that payload_fields property is populated when an uplink message is Decoded.
There is a built in decoder for Low Power Payload(LPP) which looked like the simplest option to start with.
I modified the Seeeduino LoRaWAN Over The Air Activation(OTAA) sample application and added the LPP library from Electronic Cats.
#include <LoRaWan.h>
LPP lpp(64);
char buffer[256];
void setup(void)
{
SerialUSB.begin(9600);
while(!SerialUSB);
lora.init();
memset(buffer, 0, 256);
lora.getVersion(buffer, 256, 1);
SerialUSB.print("Ver:");
SerialUSB.print(buffer);
memset(buffer, 0, 256);
lora.getId(buffer, 256, 1);
SerialUSB.print("ID:");
SerialUSB.println(buffer);
lora.setKey(NULL, NULL, "12345678901234567890123456789012");
lora.setId(NULL, "1234567890123456", "1234567890123456");
lora.setPort(10);
lora.setDeciveMode(LWOTAA);
lora.setDataRate(DR0, AS923);
lora.setDutyCycle(false);
lora.setJoinDutyCycle(false);
lora.setPower(14);
while(!lora.setOTAAJoin(JOIN, 10));
}
void loop(void)
{
bool result = false;
lpp.reset ();
// Original LPPv1 data types only these work
//
lpp.addAnalogInput( 0, 0.01234) ;
lpp.addAnalogOutput( 0, 0.56789);
lpp.addDigitalInput(0, false);
lpp.addDigitalInput(1, true);
lpp.addGPS (1, -43.5309, 172.6371, 6.192);
lpp.addAccelerometer(0, 0.0, 0.0, 1.0);
lpp.addGyrometer(1, 0.0,0.0,0.0);
lpp.addLuminosity(0, 0); // Pitch black
lpp.addLuminosity(1, 8000); // 40w fluro
lpp.addPresence(0, 0);
lpp.addPresence(1, 1);
lpp.addBarometricPressure(0,0.0);
lpp.addBarometricPressure(0,1013.25);
lpp.addRelativeHumidity (0, 50.0);
lpp.addRelativeHumidity (1, 60.0);
lpp.addTemperature (0, -273.00);
lpp.addTemperature (1, 0.0);
lpp.addTemperature (2, 100.0);
// Additional data types don't think any of these worked
//lpp.addUnixTime(1, millis());
//lpp.addGenericSensor(1, 1.23456);
//lpp.addVoltage(1, 4.5);
//lpp.addCurrent(0, 1.0);
//lpp.addFrequency (1, 50);
//lpp.addPercentage(1, 50);
//lpp.addAltitude(1, 20.5);
//lpp.addPower(1, 1500);
//lpp.addDistance(1, 120.0);
//lpp.addEnergy(1, 2.345);
//lpp.addDirection(1, -98.76);
//lpp.addSwitch(0, 1);
//lpp.addConcentration(0, 10);
//lpp.addColour(1, 255, 255, 255);
uint8_t *lppBuffer = lpp.getBuffer();
uint8_t lppLen = lpp.getSize();
SerialUSB.print("Length is: ");
SerialUSB.println(lppLen);
// Dump buffer content for debugging
PrintHexBuffer (lppBuffer, lppLen);
//result = lora.transferPacket("Hello World!", 10);
result = lora.transferPacket(lppBuffer, lppLen);
if(result)
{
short length;
short rssi;
memset(buffer, 0, sizeof(buffer));
length = lora.receivePacket(buffer, 256, &rssi);
if(length)
{
SerialUSB.print("Length is: ");
SerialUSB.println(length);
SerialUSB.print("RSSI is: ");
SerialUSB.println(rssi);
SerialUSB.print("Data is: ");
for(unsigned char i = 0; i < length; i ++)
{
SerialUSB.print("0x");
SerialUSB.print(buffer[i], HEX);
SerialUSB.print(" ");
}
SerialUSB.println();
}
}
delay( 30000);
}
void PrintHexBuffer( uint8_t *buffer, uint8_t size )
{
for( uint8_t i = 0; i < size; i++ )
{
if(buffer[i] < 0x10)
{
Serial.print('0');
}
SerialUSB.print( buffer[i], HEX );
Serial.print(" ");
}
SerialUSB.println( );
}
I then copied and saved to files the payloads from the Azure Application Insights events generated when an uplink messages were processed.
{
"app_id": "rak811wisnodetest",
"dev_id": "seeeduinolorawan4",
"hardware_serial": "1234567890123456",
"port": 10,
"counter": 1,
"is_retry": true,
"payload_raw": "AWcBEAFlAGQBAAEBAgAyAYgAqYgGIxgBJuw=",
"payload_fields": {
"analog_in_1": 0.5,
"digital_in_1": 1,
"gps_1": {
"altitude": 755,
"latitude": 4.34,
"longitude": 40.22
},
"luminosity_1": 100,
"temperature_1": 27.2
},
"metadata": {
"time": "2020-08-28T10:41:04.496594225Z",
"frequency": 923.4,
"modulation": "LORA",
"data_rate": "SF12BW125",
"coding_rate": "4/5",
"gateways": [
{
"gtw_id": "eui-b827ebfffe6c279d",
"timestamp": 3971612260,
"time": "2020-08-28T10:41:03.313471Z",
"channel": 1,
"rssi": -53,
"snr": 11.2,
"rf_chain": 0,
"latitude": -43.49885,
"longitude": 172.60095,
"altitude": 25
}
]
},
"downlink_url": "https://integrations.thethingsnetwork.org/ttn-eu/api/v2/down/rak811wisnodetest/azure-webapi-endpoint?key=ttn-account-v2.12345678901234567_12345_1234567-dduo"
}
I used JSON2Csharp to generate C# classes which would deserialise the above uplink message.
// Third version of classes for unpacking HTTP payload
public class Gps1V3
{
public int altitude { get; set; }
public double latitude { get; set; }
public double longitude { get; set; }
}
public class PayloadFieldsV3
{
public double analog_in_1 { get; set; }
public int digital_in_1 { get; set; }
public Gps1V3 gps_1 { get; set; }
public int luminosity_1 { get; set; }
public double temperature_1 { get; set; }
}
public class GatewayV3
{
public string gtw_id { get; set; }
public ulong timestamp { get; set; }
public DateTime time { get; set; }
public int channel { get; set; }
public int rssi { get; set; }
public double snr { get; set; }
public int rf_chain { get; set; }
public double latitude { get; set; }
public double longitude { get; set; }
public int altitude { get; set; }
}
public class MetadataV3
{
public string time { get; set; }
public double frequency { get; set; }
public string modulation { get; set; }
public string data_rate { get; set; }
public string coding_rate { get; set; }
public List<GatewayV3> gateways { get; set; }
}
public class PayloadV3
{
public string app_id { get; set; }
public string dev_id { get; set; }
public string hardware_serial { get; set; }
public int port { get; set; }
public int counter { get; set; }
public bool is_retry { get; set; }
public string payload_raw { get; set; }
public PayloadFieldsV3 payload_fields { get; set; }
public MetadataV3 metadata { get; set; }
public string downlink_url { get; set; }
}
I added a new to controller to my application which used the generated classes to deserialise the body of the POST from the TTN Application Integration.
[Route("[controller]")]
[ApiController]
public class ClassSerialisationV3Fields : ControllerBase
{
private static readonly ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
public string Index()
{
return "move along nothing to see";
}
[HttpPost]
public IActionResult Post([FromBody] PayloadV3 payload)
{
// Check that the post data is good
if (!this.ModelState.IsValid)
{
log.WarnFormat("ClassSerialisationV3Fields validation failed {0}", this.ModelState.Messages());
return this.BadRequest(this.ModelState);
}
log.Info($"DevEUI:{payload.hardware_serial} Payload Base64:{payload.payload_raw} analog_in_1:{payload.payload_fields.analog_in_1} digital_in_1:{payload.payload_fields.digital_in_1} gps_1:{payload.payload_fields.gps_1.latitude},{payload.payload_fields.gps_1.longitude},{payload.payload_fields.gps_1.altitude} luminosity_1:{payload.payload_fields.luminosity_1} temperature_1:{payload.payload_fields.temperature_1}");
return this.Ok();
}
}
I then updated the TTN application integration to send messages to my new endpoint. In the body of the Application Insights events I could see the devEUI, port, and the payload fields had been extracted from the message.
DevEUI:1234567890123456 Payload Base64:AWcBEAFlAGQBAAEBAgAyAYgAqYgGIxgBJuw= analog_in_1:0.5 digital_in_1:1 gps_1:4.34,40.22,755 luminosity_1:100 temperature_1:27.2
This arrangement was pretty nasty and sort of worked but in the “real world” would not have been viable. I would need to generate lots of custom classes for each application taking into account the channel numbers (e,g, analog_in_1,analog_in_2) and datatypes used.
I also explored which datatypes were supported by the TTN decoder, after some experimentation (Aug 2019) it looks like only the LPPV1 ones are.
- AnalogInput
- AnalogOutput
- DigitalInput
- DigitalOutput
- GPS
- Accelerometer
- Gyrometer
- Luminosity
- Presence
- BarometricPressure
- RelativeHumidity
- Temperature
What I need is a more flexible way to stored and decode payload_fields property..
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