Azure Service Bus Dead Letter Queue Drain

DeadLetterDrain.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Azure.Messaging.ServiceBus" Version="7.1.2"/>
    <PackageReference Include="CsvHelper" Version="27.0.2"/>
  </ItemGroup>
</Project>

Program.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using Azure.Messaging.ServiceBus;
using CsvHelper;

string connectionString = @"";
string topicName = "";
string subscriptionName = "";

await using var client = new ServiceBusClient(connectionString);

var receiver = client.CreateReceiver(topicName, subscriptionName, new ServiceBusReceiverOptions
{
    SubQueue = SubQueue.DeadLetter,
});


List<DeadLetterQueueEntry> entries = new();
ServiceBusReceivedMessage message = null;

try
{
    while (true)
    {
        message = await receiver.ReceiveMessageAsync(TimeSpan.FromSeconds(5));
        if (message == null)
        {
            break;
        }
        entries.Add(new DeadLetterQueueEntry(message.DeadLetterReason, message.EnqueuedTime, message.Body.ToString()));
        await receiver.CompleteMessageAsync(message);
        Console.WriteLine("Successfully pulled a new message from DLQ.");
    }
}
catch
{
    await receiver.AbandonMessageAsync(message);
}
finally
{
    // A safer alternative would be to write each out as received and instead flush here.
    // See https://joshclose.github.io/CsvHelper/getting-started/

    using StreamWriter writer = new("messages.csv");
    using CsvWriter csv = new(writer, CultureInfo.InvariantCulture);

    csv.WriteRecords(entries);
}

public record DeadLetterQueueEntry(string Reason, DateTimeOffset EqueuedTime, string MessageBody);