OpenServiceBus.Core 1.0.4

OpenServiceBus

A zero-dependency, embeddable Azure Service Bus emulator for .NET. Speaks real AMQP 1.0 over TCP and WebSocket so Azure.Messaging.ServiceBus, Azure Functions ServiceBusTrigger, and any other Service Bus client connect unmodified.

Why this exists

Microsoft ships an official Service Bus emulator, but it needs Docker + SQL Server and is EULA-gated. OpenServiceBus is the MIT-licensed alternative: a single-node Service Bus emulator that runs as a NuGet inside your test fixture, as a docker run, or as a standalone executable - no SQL Server, no licensing dance, no 5-minute container boot.

It implements the full Service Bus feature surface that real client code uses: queues, topics + subscriptions (SQL/correlation filters), sessions, duplicate detection, auto-forwarding, transactions, defer, scheduled messages, TTL, peek-lock with renewal, dead-letter routing, exposed over both plain AMQP and AMQP-over-WebSocket, with native OpenTelemetry instrumentation throughout.

Install

From source

git clone https://github.com/mauritsarissen/OpenServiceBus
cd OpenServiceBus
dotnet run --project src/OpenServiceBus.Host

The host binds amqp://localhost:5672 (Service Bus SDK) and http://localhost:5300 (REST management + /health).

Docker

docker run -d --name openservicebus \
  -p 5672:5672 \
  -p 5300:5300 \
  -p 5400:5400 \
  -v osb-data:/data \
  mauritsarissen/openservicebus:latest

The image runs the broker and the Explorer UI side-by-side. SQLite-backed at /data/broker.db - mount the named volume and queues + messages survive container recreates. See Docker for the compose recipe, every env var, and the WebSocket-transport setup.

Connect

The same connection string works against either install path:

Endpoint=sb://localhost:5672;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=SAS_KEY_VALUE;UseDevelopmentEmulator=true

await using var client = new ServiceBusClient(
    "Endpoint=sb://localhost:5672;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=SAS_KEY_VALUE;UseDevelopmentEmulator=true");

await client.CreateSender("orders").SendMessageAsync(new ServiceBusMessage("hello"));
var msg = await client.CreateReceiver("orders").ReceiveMessageAsync();

UseDevelopmentEmulator=true tells the Azure SDK to skip TLS and accept the broker on plain TCP - the same trick the official Microsoft emulator uses.

As a NuGet inside your tests

If you don't want any external process at all, install the test fixture and run the broker inside your test process:

dotnet add package OpenServiceBus.Testing

Published on nuget.org - no extra source needed. (GitHub Packages also mirrors every release, see Contributing.)

await using var host = await OpenServiceBusTestHost.StartAsync();
await host.CreateQueueAsync("orders");

await using var client = new ServiceBusClient(host.ConnectionString);
await client.CreateSender("orders").SendMessageAsync(new ServiceBusMessage("hello"));

var receiver = client.CreateReceiver("orders");
var msg = await receiver.ReceiveMessageAsync();
await receiver.CompleteMessageAsync(msg);

One disposable host, free ephemeral port, full AMQP semantics - run thousands of these in parallel. See Testing for time-travel, parity testing, and the options surface.

Feature recipes

Topics + filters (SQL / correlation / true / false)

await host.Topics.CreateTopicAsync(new TopicDescriptor { Name = "events" });
await host.Topics.CreateSubscriptionAsync(new SubscriptionDescriptor
    { TopicName = "events", Name = "eu" });
await host.Topics.CreateOrReplaceRuleAsync(new RuleDescriptor
{
    TopicName = "events", SubscriptionName = "eu", Name = "EuOnly",
    Filter = new SqlFilter("region = 'eu' AND priority >= 5"),
});

await client.CreateSender("events").SendMessageAsync(new ServiceBusMessage("hi-eu")
{
    ApplicationProperties = { ["region"] = "eu", ["priority"] = 7 }
});

→ Topics and Subscriptions

Sessions

await host.Queues.CreateAsync(new QueueDescriptor { Name = "sessioned", RequiresSession = true });
var sender = client.CreateSender("sessioned");
await sender.SendMessageAsync(new ServiceBusMessage("a") { SessionId = "S" });
await sender.SendMessageAsync(new ServiceBusMessage("b") { SessionId = "S" });

var session = await client.AcceptSessionAsync("sessioned", "S");
var first  = await session.ReceiveMessageAsync(); // "a"
var second = await session.ReceiveMessageAsync(); // "b"

→ Sessions

Transactions (TransactionScope)

using (var scope = new TransactionScope(TransactionScopeAsyncFlowOption.Enabled))
{
    await sender.SendMessageAsync(new ServiceBusMessage("a"));
    await receiver.CompleteMessageAsync(previouslyReceivedMessage);
    scope.Complete(); // commit; without this everything rolls back
}

→ Transactions

Auto-forwarding

await host.Queues.CreateAsync(new QueueDescriptor { Name = "downstream" });
await host.Queues.CreateAsync(new QueueDescriptor
    { Name = "ingress", ForwardTo = "downstream" });
// Sends to "ingress" land on "downstream" - invisible to senders.

→ Auto-Forwarding

Duplicate detection

await host.Queues.CreateAsync(new QueueDescriptor
{
    Name = "deduped",
    RequiresDuplicateDetection = true,
    DuplicateDetectionHistoryTimeWindow = TimeSpan.FromMinutes(5),
});

await sender.SendMessageAsync(new ServiceBusMessage("first")  { MessageId = "k" });
await sender.SendMessageAsync(new ServiceBusMessage("second") { MessageId = "k" }); // silently dropped

→ Duplicate Detection

Declarative config.json bootstrap

OpenServiceBus reads the same config.json format as the official Microsoft emulator:

{
  "UserConfig": {
    "Namespaces": [
      {
        "Name": "demo",
        "Queues": [
          {
            "Name": "orders",
            "Properties": {
              "LockDuration": "PT1M",
              "MaxDeliveryCount": 3,
              "RequiresSession": false,
              "DefaultMessageTimeToLive": "PT1H"
            }
          }
        ]
      }
    ]
  }
}

Resolution: --config <path> → OPENSERVICEBUS_CONFIG env var → config.json in the host's content-root. Full schema in Configuration.

Persistence (SQLite)

export OPENSERVICEBUS__STORAGE__MODE=Sqlite
export OPENSERVICEBUS__STORAGE__DATASOURCE=/data/broker.db
dotnet run --project src/OpenServiceBus.Host

→ Persistence

AMQP-over-WebSocket

export OPENSERVICEBUS__WEBSOCKETS__ENABLED=true
dotnet run --project src/OpenServiceBus.Host

await using var client = new ServiceBusClient(
    "Endpoint=sb://localhost:5673;...;UseDevelopmentEmulator=true",
    new ServiceBusClientOptions { TransportType = ServiceBusTransportType.AmqpWebSockets });

→ WebSocket Transport

OpenTelemetry

services.AddOpenTelemetry()
    .WithTracing(b => b.AddSource(OpenServiceBusDiagnostics.SourceName).AddOtlpExporter())
    .WithMetrics(b => b.AddMeter(OpenServiceBusDiagnostics.SourceName).AddOtlpExporter());

→ OpenTelemetry

Configuration

The host honors these appsettings.json / environment variable keys:

Full reference: Configuration.

Samples

Each sample is self-contained: it ships a docker-compose.yml, a config.json, and a README.md that explains what it demonstrates and how to run it.

• samples/OpenServiceBus.Samples.QuickStart - minimal console send/receive against an emulator container.
• samples/OpenServiceBus.Samples.TopicsAndFilters - pub-sub with SQL + correlation filter rules.
• samples/OpenServiceBus.Samples.Sessions - session-locked workers with per-session FIFO ordering.
• samples/OpenServiceBus.Samples.WorkerService - Microsoft.Extensions.Hosting background-worker pattern.
• samples/OpenServiceBus.Samples.Functions - minimal Azure Functions ServiceBusTrigger app (the integration-test target).
• samples/OpenServiceBus.Samples.FunctionsTriggerDemo - interactive multi-trigger Functions app driven via the Explorer or HTTP.

See samples/README.md for the full index and a quick chooser table.

Documentation

Multi-page guides in docs/ - also published to the GitHub Wiki:

• Getting Started - install + first send/receive
• Configuration - config.json, env vars, every option
• Architecture - assemblies, AMQP layer, store contracts
• Docker - image, compose, env vars, persistence
• Persistence - SQLite store, schema, restart semantics
• Topics and Subscriptions - filters, rules, fan-out
• Sessions - session-locked receivers, state, ordering
• Auto-Forwarding - ForwardTo, DLQ forwarding, cycles
• Transactions - coordinator, TransactionScope, semantics
• Duplicate Detection - window, observed behavior
• WebSocket Transport - bridge setup, ports, client config
• OpenTelemetry - source names, attributes, gauges
• Explorer UI - running the browser console
• Testing - OpenServiceBusTestHost, fake-time, parity tests
• Contributing - repo layout, conventions, releasing
• Roadmap - what's next

Development

dotnet build         # multi-targets net8.0 + net10.0
dotnet test          # full regression suite (~210 tests)
docker build -t openservicebus:dev .

The Azure Functions integration test requires func (Azure Functions Core Tools v4) and the .NET 8 runtime; it skips when either is missing. See Contributing for repo conventions, the release flow, and how to add a new milestone.

License

MIT © Maurits Arissen and OpenServiceBus contributors.