AWS SQS DLQ Downloader using .NET 10 single-file app. Downloads all messages from an SQS queue or DLQ to a .jsonl file, flushing to disk before deletion to avoid data loss. Supports AWS profile/region config, queue name or URL, and a --dry-run mode for safe testing without deleting messages.

sqs_dump.cs

// Run with: dotnet run sqs_dump.cs -- --queue-url https://sqs.eu-west-1.amazonaws.com/123456789012/my-dlq
// Optional: --out dlq.jsonl --region eu-west-1 --profile default --visibility 300 --wait 20 --queue-name my-dlq --dry-run

#:package AWSSDK.SQS@3.7.500.5

using Amazon;
using Amazon.SQS;
using Amazon.SQS.Model;
using Amazon.Runtime;
using Amazon.Runtime.CredentialManagement;
using System.Text;
using System.Text.Json;

string? Arg(string name)
{
    for (int i = 0; i < args.Length - 1; i++)
        if (args[i].Equals(name, StringComparison.OrdinalIgnoreCase))
            return args[i + 1];
    return null;
}

bool HasFlag(string flag) =>
    args.Any(a => a.Equals(flag, StringComparison.OrdinalIgnoreCase));

var queueUrl   = Arg("--queue-url") ?? Environment.GetEnvironmentVariable("QUEUE_URL");
var queueName  = Arg("--queue-name");
var region     = Arg("--region")     ?? Environment.GetEnvironmentVariable("AWS_REGION") ?? "eu-west-1";
var profile    = Arg("--profile")    ?? Environment.GetEnvironmentVariable("AWS_PROFILE") ?? "default";
var outPath    = Arg("--out")        ?? $"sqs-dlq-{DateTimeOffset.UtcNow:yyyyMMdd-HHmmss}.jsonl";
var visibility = int.TryParse(Arg("--visibility") ?? "180", out var vis) ? vis : 180;
var waitSecs   = int.TryParse(Arg("--wait") ?? "20", out var wt) ? wt : 20;
var dryRun     = HasFlag("--dry-run");

var config = new AmazonSQSConfig();
if (!string.IsNullOrWhiteSpace(region))
    config.RegionEndpoint = RegionEndpoint.GetBySystemName(region);

AWSCredentials? creds = null;
if (!string.IsNullOrWhiteSpace(profile) &&
    new CredentialProfileStoreChain().TryGetAWSCredentials(profile, out var c))
    creds = c;

using var sqs = creds is null ? new AmazonSQSClient(config) : new AmazonSQSClient(creds, config);

if (string.IsNullOrWhiteSpace(queueUrl) && !string.IsNullOrWhiteSpace(queueName))
{
    var urlResp = await sqs.GetQueueUrlAsync(new GetQueueUrlRequest { QueueName = queueName });
    queueUrl = urlResp.QueueUrl;
}

if (string.IsNullOrWhiteSpace(queueUrl))
{
    Console.Error.WriteLine("Usage: dotnet run app.cs -- --queue-url <url> [--queue-name name] [--out file.jsonl] [--region eu-west-1] [--profile default] [--visibility 180] [--wait 20] [--dry-run]");
    Environment.ExitCode = 2;
    return;
}

Console.WriteLine($"Downloading from: {queueUrl}");
Console.WriteLine($"Writing to      : {outPath}");
if (dryRun) Console.WriteLine("Dry-run mode: No messages will be deleted.");

var sysAttrs = new List<string> { "All" };
var msgAttrs = new List<string> { "All" };

using var fs = new FileStream(outPath, FileMode.Append, FileAccess.Write, FileShare.Read);
using var writer = new StreamWriter(fs, new UTF8Encoding(false)) { AutoFlush = true };

var cancelled = false;
Console.CancelKeyPress += (_, e) => { e.Cancel = true; cancelled = true; };

int total = 0, emptyPolls = 0, emptyLimit = 3;

while (!cancelled)
{
    var req = new ReceiveMessageRequest
    {
        QueueUrl = queueUrl!,
        MaxNumberOfMessages = 10,
        WaitTimeSeconds = waitSecs,
        VisibilityTimeout = visibility,
        MessageSystemAttributeNames = sysAttrs,
        MessageAttributeNames = msgAttrs
    };

    var resp = await sqs.ReceiveMessageAsync(req);
    if (resp.Messages.Count == 0)
    {
        if (++emptyPolls >= emptyLimit) break;
        continue;
    }

    emptyPolls = 0;

    foreach (var m in resp.Messages)
    {
        var line = new
        {
            m.MessageId,
            m.MD5OfBody,
            m.MD5OfMessageAttributes,
            Body = m.Body,
            Attributes = m.Attributes,
            MessageAttributes = m.MessageAttributes?.ToDictionary(
                kv => kv.Key,
                kv => new {
                    kv.Value.DataType,
                    kv.Value.StringValue,
                    BinaryValueBase64 = kv.Value.BinaryValue != null
                        ? Convert.ToBase64String(kv.Value.BinaryValue.ToArray())
                        : null
                })
        };

        await writer.WriteLineAsync(JsonSerializer.Serialize(line));
        writer.Flush();
        fs.Flush(true);

        if (dryRun)
        {
            Console.WriteLine($"[Dry-run] Would delete: {m.MessageId}");
            total++;
        }
        else
        {
            try
            {
                Console.WriteLine($"Deleting: {m.MessageId}");
                await sqs.DeleteMessageAsync(queueUrl!, m.ReceiptHandle);
                total++;
            }
            catch (Exception ex)
            {
                Console.Error.WriteLine($"Delete failed for {m.MessageId}: {ex.Message}");
                try { await sqs.ChangeMessageVisibilityAsync(queueUrl!, m.ReceiptHandle, Math.Min(visibility, 300)); } catch { }
            }
        }
    }
}

Console.WriteLine($"Done. {(dryRun ? "Tested" : "Downloaded and deleted")} {total} messages.");