Azure function IoTHub: Error indexing method Value cannot be null. (Parameter 'connectionString')

Question

Am trying to set a trigger from an Azure function to read all data that comes from my IoT hub. For that, I followed this tutorial.

After setting the connection string inside my local settings, when I try to launch my function, I get the following error:

The 'functionName' function is in error: Microsoft.Azure.WebJobs.Host: Error indexing method 'Functions.functionName'. Microsoft.WindowsAzure.Storage: Value cannot be null. (Parameter 'connectionString').

I have tried to add the endpoint as a servicebus, or directly as a hostname, but in both I have the same error.

As ServiceBus: Endpoint=sb://{hubname}.servicebus.windows.net/;SharedAccessKeyName={keyname};SharedAccessKey={accesskeyname};
As hostname: HostName={hostName}.azure-devices.net;SharedAccessKeyName={keyname};SharedAccessKey={accesskeyname}

To add further clarify, I will show my implementation:

local.settings.json

{
    "IsEncrypted": false,
    "Values": {
        "AzureWebJobsStorage": "",
        "FUNCTIONS_WORKER_RUNTIME": "java",
        "app_trigger_hub_name": "{hubname}",
        "app_trigger_connection": "Endpoint=sb://{hubname}.servicebus.windows.net/;SharedAccessKeyName={accessKey};SharedAccessKey={sharedKey}",
    }
}

Azure Function trigger

 @FunctionName("functionName")
  public void eventHubProcessor(
  @EventHubTrigger(name = "functionName", eventHubName = "%app_trigger_hub_name%",
  connection = "app_trigger_connection") String message,
  final ExecutionContext context) {
  context.getLogger().info(message);
  }

Credentials from azure

EDIT

After some trial & error I managed to get the connection using the servicebus, but still not working. Now when I start the function, I got the following error:

The listener for function 'Functions.function' was unable to start. Microsoft.Azure.EventHubs.Processor: Encountered error while fetching the list of EventHub PartitionIds. System.Private.CoreLib: nodename nor servname provided, or not known.

byteArrayJake · Accepted Answer · 2022-02-04 08:33:17Z

0

First of all, are you using a IoTHub or a EventHub? In C# you use the iothub attribute: "IoTHubTrigger".

E.g:

@FunctionName("ehprocessor")
public void eventHubProcessor(
  @IoTHubTrigger(name = "msg",
                  eventHubName = "myeventhubname",
                  connection = "myconnvarname") String message,
       final ExecutionContext context )
       {
          context.getLogger().info(message);
 }

using IoTHubTrigger = Microsoft.Azure.WebJobs.EventHubTriggerAttribute;

And for the connectionString you use the "Event Hub compatible endpoint", that you can find under "Built-in endpoints" in the azure portal.

I saw your edited part now, have you tried to empty your eventhub container locally? "azure-webjobs-eventhub"? that have solved many wierd errors for me.

edited Feb 4, 2022 at 8:33

answered Feb 3, 2022 at 13:41

byteArrayJake

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3 Comments

maro01507 Over a year ago

I totally forgot about this. What I did was using a Built-in endpoint as the connection String.

byteArrayJake Over a year ago

@maro01507 cool, so you have solved the problem? :)

maro01507 Over a year ago

yep, thanks for trying to help anyway.

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