Error with v4 EventHub trigger and cardinality many

[rvk86]

I'm upgrading my EventHub trigger to the v4 programming model. When I run the trigger locally and publishing a message the code works fine with cardinality: "one", but when I switch to cardinality: "many" I'm receiving the following error:

[2023-11-03T09:33:04.431Z] Executed 'Functions.location-updates' (Failed, Id=eac578f2-f16e-470b-8474-601a02d0e0b8, Duration=59ms)
[2023-11-03T09:33:04.432Z] System.Private.CoreLib: Exception while executing function: Functions.location-updates. Microsoft.Azure.WebJobs.Host: Exception binding parameter 'eventHubTrigger1'. Microsoft.Azure.WebJobs.Host: Binding parameters to complex objects (such as 'Object') uses Json.NET serialization. 
[2023-11-03T09:33:04.432Z] 1. Bind the parameter type as 'string' instead of 'Object' to get the raw values and avoid JSON deserialization, or
[2023-11-03T09:33:04.432Z] 2. Change the queue payload to be valid json. The JSON parser failed: Unexpected character encountered while parsing value: . Path '', line 0, position 0.

Repro steps

1. Run the below code locally with func start
2. Publish a message to the EventHub the trigger is listening to
3. Observe the error being thrown

import { app } from "@azure/functions";

const eventHubTrigger = async function (
    eventHubMessages: any
): Promise<void> {
    console.log(eventHubMessages);
};

app.eventHub("location-updates", {
    eventHubName: process.env.EVENT_HUB_NAME,
    connection: "EVENT_HUB_CONNECTION",
    handler: eventHubTrigger,
    cardinality: "many", // if this is set to "one" the trigger works fine
});

Expected behavior

I'd expect the handler function to run with an array of strings as the first argument.

Actual behavior

The emulator throws the error as shown above

[ejizba]

Hi @rvk86 this is somewhat of a known problem, tracked by Azure/azure-functions-eventhubs-extension#118

The recommended workarounds are to either make sure your event hub messages are JSON-parseable or to add dataType: "string" to your configuration.

[rvk86]

Hi @ejizba, thanks for your response. Since my messages are in Avro format, your first workaround is not feasible. I'd love to try the second, but with the v4 programming model I wouldn't know where to define the dataType. Can you help me with that?

[ejizba]

Try this:

app.eventHub("location-updates", {
    eventHubName: process.env.EVENT_HUB_NAME,
    connection: "EVENT_HUB_CONNECTION",
    handler: eventHubTrigger,
    cardinality: "many", // if this is set to "one" the trigger works fine
    dataType: "string",
});

We don't have full support for "dataType" yet in the TypeScript types (tracked here), but functionality-wise it should work. If TypeScript complains, casting the options object to "any" is an easy way to suppress the error:

app.eventHub("location-updates", <any>{

[rvk86]

specifying the dataType in the eventHubOptions indeed solves the problem! Would be nice to update the type definitions to avoid this confusion.

Thanks for your help :)

[ejizba]

Nice! Closing in favor of #72 and Azure/azure-functions-eventhubs-extension#118