Azure Functions: StatusCode cannot be set because the response has already started-CodePudding

I am trying to stream data from my Azure Function and all is fine but I get an error after it has executed.

This is the code:

[FunctionName("QueryData")]
public async Task QuerySingleMessages([HttpTrigger(AuthorizationLevel.Function, "post", Route = null)] HttpRequest req)
{
     var message = await req.GetPostMessage<Message>();
     
     var response = req.HttpContext.Response; 
     response.StatusCode = 200;
     response.ContentType = "application/json-data-stream";
            
     var sw = new StreamWriter(response.Body);
     
     foreach (var msg in this.messageReaderService.FindLatestMessages(message.keys))
     {
         var json = System.Text.Json.JsonSerializer.Serialize(
                    msg,
                    new JsonSerializerOptions {PropertyNameCaseInsensitive = false});
         await sw.WriteAsync(json);
     }

     await sw.FlushAsync();
     await sw.DisposeAsync();
}

this is the error:

[2022-05-06T15:15:17.034Z] Executed 'QueryData' (Succeeded, Id=df70d5a7-37d7-40ef-b446-ecceb943e454, Duration=1350ms)
[2022-05-06T15:15:17.047Z] An unhandled host error has occurred.
[2022-05-06T15:15:17.048Z] Microsoft.AspNetCore.Server.Kestrel.Core: StatusCode cannot be set because the response has already started.

Is there a configuration (or something else) I can change so that I can stop the host error to occur?

Thanks

CodePudding user response：

After reproducing from our end we could able to get this work when we tried fixing the return type and return the EmptyResult i.e., return new EmptyResult();.

[FunctionName("Function1")]
        public static async Task<EmptyResult> Run(
            [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
            ILogger log)
        {
            var message = await req.GetPostMessage<Message>();

            var response = req.HttpContext.Response;
            response.StatusCode = 200;
            response.ContentType = "application/json-data-stream";

            var sw = new StreamWriter(response.Body);

            foreach (var msg in this.messageReaderService.FindLatestMessages(message.keys))
            {
                var json = System.Text.Json.JsonSerializer.Serialize(
                           msg,
                           new JsonSerializerOptions { PropertyNameCaseInsensitive = false });
                await sw.WriteAsync(json);
            }

            await sw.FlushAsync();
            await sw.DisposeAsync();

            return new EmptyResult();
        }