CosmosDBTrigger Alters DateTimeOffset Format in Azure Function Isolated Process

[JarFrank]

I'm encountering an issue with the CosmosDBTrigger in an Azure Function using the isolated process model. When documents are triggered by changes in a Cosmos DB collection, the CosmosDBTrigger seems to alter the format of DateTimeOffset fields in the JSON payload.

Repro steps

Set up an Azure Function with a CosmosDBTrigger to monitor changes in a Cosmos DB collection.

public class TriggerFunction(ILoggerFactory loggerFactory)
{
    private readonly ILogger _logger = loggerFactory.CreateLogger<Function>();

    [Function("TriggerFunction")]
    public void Run([CosmosDBTrigger(
        databaseName: "my-database",
        containerName: "my-container",
        Connection = "ConnectionStrings:Cosmos",
        LeaseContainerName = "leases",
        StartFromBeginning = true,
        LeaseContainerPrefix = "my-",
        CreateLeaseContainerIfNotExists = true)] string input)
    {
        _logger.LogInformation("Migration {input}", input);
    }
}

1. Insert a document into the Cosmos DB collection:

{
    "id": "1",
    "TransactionDate": "2023-07-04T12:00:00+00:00"
}

2. The CosmosDBTrigger function receives:

{
    "id": "1",
    "TransactionDate": "2023-07-04T14:00:00+02:00"
}

Expected behavior

The CosmosDBTrigger should pass the document as-is without altering the format or values.

Actual behavior

The date field in the JSON document is modified.

Known workarounds

none.

Related information

• Azure Function 4.x - isolated process
• Language C#
• Packages:
  Microsoft.Azure.Functions.Worker, Version="1.22.0"
  Microsoft.Azure.Functions.Worker.Extensions.CosmosDB, Version="4.9.0"
  Microsoft.Azure.Functions.Worker.Extensions.Http, Version="3.2.0"
  Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore, Version="1.3.2"
  Microsoft.Azure.Functions.Worker.Sdk, Version="1.17.2"
  Microsoft.ApplicationInsights.WorkerService, Version="2.22.0"
  Microsoft.Azure.Functions.Worker.ApplicationInsights, Version="1.2.0"

[ealsur]

This seems related to Date Time Handling. When the raw JSON comes from the service, in order to bind it to string (the type on your trigger), it gets serialized through Newtonsoft.Json (the default engine for Cosmos DB SDK).

Newtonsoft.Json has a default Json serialization behavior for dates which does DateTime conversion with timezones.

References:

• https://www.newtonsoft.com/json/help/html/datesinjson.htm
• https://stackoverflow.com/a/62199568/5641598

You can probably set it on the global JsonSerializerSettings. I am not an expert in the Isolated Process world though to know if that will work.

[ealsur]

Also, the correct repo is https://github.com/Azure/azure-functions-dotnet-worker/issues

The nuget you are using is not from this repo.