Azure Function TextWriter stream is appending to file and not overwriting - do I need to wrap in a using statement?

Question

I have an Azure Storage account where I upload a file. The file upload takes place in an Azure Function (Blob trigger).

Everything works as expected, however, if I trigger the Function, three times, the file is appended with previous three sessions data. I don't think I am disposing of the stream correctly.

 public void Run(
        [BlobTrigger("raw/{name}")] Stream input,
        [Blob("data/{name}", FileAccess.Write)] TextWriter output,
        string name,
        ILogger log)

I am then writing to the output as follows:

output.WriteLine(data);

I am not sure how to wrap this in a using statement.

Can anyone advise?

Answer 1

Here is the code that worked for me where each time I'm triggering the function the file is getting overwritten with the current triggered data.

using System;
using System.IO;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Host;
using Microsoft.Extensions.Logging;

namespace FunctionAppTW
{
    public static class Function1
    {
        [FunctionName("Function1")]
        public static void Run([BlobTrigger("raw/{name}", Connection = "")] Stream input, [Blob("data/{name}", FileAccess.Write)] TextWriter output, string name, ILogger log)
        {

            StreamReader reader = new StreamReader(input);
            string data = reader.ReadToEnd();

            output.WriteLine(data);
        }
    }
}

RESULT:

Answer 2

I've run into this issue before myself. I can't recall but I used dependency injection in my functions app. My implementation code kept the stream alive and would aggregate previous runs when using just the output.writeline() statement.

I had to close and dispose of the previous session before each and every method call.