Blob Outstream on Azure Function

Question

i have this function

 [FunctionName("Func")]
 public async Task Run(
         [TimerTrigger("1 1 8-23 * * 1-5")] TimerInfo timerInfo,
         [Blob("metrics/accepted.json", FileAccess.Read, Connection = "AzureWebJobsStorage")] string json,
         [Blob("metrics/accepted.json", FileAccess.Write, Connection = "AzureWebJobsStorage")] Stream outputFile,
         ILogger log
 )
 {
      string out = await doThing(json);
      if (out != "") {
         byte[] byteArray = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(resp));
          await outputFile.WriteAsync(byteArray, 0, byteArray.Length);
      }
}

After adding a breakpoint, the file is emptied when it populates the stream ? Is there someway to prevent this from happening ?

Answer 1

After adding a breakpoint, the file is emptied when it populates the stream ? Is there someway to prevent this from happening ?

The issue you are facing, because you are trying to read and write on the same file which is resulting the concurrency issue, and the data of the file is being emptied because output binding overwrites content of the file.

You need to write it on the different file.

This code worked for me. Function1.cs

using System;
using System.IO;
using System.Reflection.Metadata;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;

namespace FunctionApp3
{
    public class Function1
    {
        [FunctionName("Function1")]
        public static async Task Run([TimerTrigger("0 */5 * * * *")] TimerInfo myTimer,
         [Blob("metrics/accepted.json", FileAccess.Read, Connection = "AzureWebJobsStorage")] Stream json,
         [Blob("metrics/accepted2.json", FileAccess.Write, Connection = "AzureWebJobsStorage")] Stream outputFile,
         ILogger log)

        {
            log.LogInformation($"C# Timer trigger function executed at: {DateTime.Now}");

            JsonModel jsonObject;
            using (var reader = new StreamReader(json))
            {
                var jsonContent = await reader.ReadToEndAsync();

                log.LogInformation($"content of accepted.json : {jsonContent}");

                jsonObject = JsonConvert.DeserializeObject<JsonModel>(jsonContent);
                jsonObject.Platform = "StackOverflow";

            }
            byte[] byteArray = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(jsonObject, Formatting.Indented));

            await outputFile.WriteAsync(byteArray,0,byteArray.Length);

        }

        public class JsonModel
        {
            public string FirstName { get; set; }
            public string LastName { get; set; }
            public string Platform { get; set; }
        }
    }
}

OUTPUT:

accepted.json:

{
 "FirstName": "Vivek",
 "LastName": "Shandilya"
}

Functions:

        Function1: timerTrigger

For detailed output, run func with --verbose flag.
[2024-01-24T07:00:57.091Z] Executing 'Function1' (Reason='Timer fired at 2024-01-24T12:30:54.2878940+05:30', Id=56819861-b602-447c-82ea-5dab57849da1)
[2024-01-24T07:00:57.097Z] Trigger Details: UnscheduledInvocationReason: IsPastDue, OriginalSchedule: 2024-01-24T12:10:00.0000000+05:30
[2024-01-24T07:00:57.172Z] C# Timer trigger function executed at: 1/24/2024 12:30:57 PM
[2024-01-24T07:00:57.490Z] content of accepted.json : {
[2024-01-24T07:00:57.494Z]      "FirstName":"Vivek",
[2024-01-24T07:00:57.499Z]      "LastName":"Shandilya"
[2024-01-24T07:00:57.503Z] }
[2024-01-24T07:00:57.665Z] Host lock lease acquired by instance ID '000000000000000000000000AAE5F384'.
[2024-01-24T07:00:58.538Z] Executed 'Function1' (Succeeded, Id=56819861-b602-447c-82ea-5dab57849da1, Duration=4181ms)

accepted2.json:

{
  "FirstName": "Vivek",
  "LastName": "Shandilya",
  "Platform": "StackOverflow"
}