In-Memory Transport

ID: transport.inmemory
Name: In-memory transport
Maturity: GA
Summary: In-process channel broker used for fast tests and local workflows while preserving transport contracts.

What It Does

InMemoryTransportModule registers InMemoryTransportBroker, InMemoryPublisher, and InMemoryConsumer. Messages are queued by destination inside process memory and delivered through the same TransportMessage contract used by external brokers.

Each destination admits at most InMemoryTransportOptions.DestinationCapacity unsettled deliveries, including queued and currently handled messages. The default is 1024. When the limit is reached, PublishAsync waits asynchronously until a delivery settles or the caller cancels. LiteBus uses the lossless BoundedChannelFullMode.Wait behavior documented in the current .NET channels guidance.

Ack behavior is explicit. AcceptAsync and DiscardAsync release the delivery's capacity reservation. ReturnToQueueAsync re-enqueues with Redelivered = true and retains the reservation, so a waiting publisher cannot take the only slot and deadlock redelivery.

bus.AddInMemoryTransport(new InMemoryTransportOptions
{
    DestinationCapacity = 256
});

Public Surface

API	Role
`InMemoryTransportOptions.DestinationCapacity`	Per-destination queued and in-flight bound
`InMemoryTransportModule`	Registers in-memory transport services
`InMemoryTransportBroker`	Queue registry keyed by destination
`InMemoryPublisher.PublishAsync`	Enqueue publish request body and headers
`InMemoryConsumer.StartAsync`	Dequeue and invoke handler loop
`InMemoryDestinationEndpoint`	Destination queue and synchronization
`InMemoryPendingDelivery`	Delivery snapshot with redelivery bit
`LiteBusInMemoryTelemetry.MeterName`	Reserved in-memory adapter meter

Packages

LiteBus.Transport.InMemory

Requires

transport.publish-consume-contracts
transport.manual-acknowledgement
transport.single-broker-registration

Invariants

Transport is process-local and not durable.
Destination capacity is positive, applies independently to every destination, and is validated during composition.
Full destinations wait for capacity; the transport does not drop old or new writes.
Redelivery requires explicit ReturnToQueueAsync or exception path through invoker behavior.
Shared transport metrics are tagged inmemory.

Non-Goals

Cross-process messaging.
Durability and replay across restart.
Replacing external brokers for production workloads.

Observability

Metrics

Item	Value
Shared meter	`LiteBus.Transport`
Broker tag	`litebus.transport.broker="inmemory"`
Shared gauges	`litebus.transport.circuit_breaker.open`, `litebus.transport.circuit_breaker.failure_count`
Reserved adapter meter	`LiteBus.Transport.InMemory`
OpenTelemetry registration	`AddLiteBusTransportMetrics()`

Tracing

Activity source LiteBus.Transport
Spans send {destination} and process {destination} with messaging.system=litebus_in_memory

Test Coverage

Covered

Test method	Project
`PublishAndConsume_ShouldDeliverMessageToConsumer`	`LiteBus.Transport.UnitTests` (`InMemory/`)
`ReturnToQueue_ShouldRedeliverMessage`	`LiteBus.Transport.UnitTests` (`InMemory/`)
`HandlerThrow_ShouldRequeueMessageByDefault`	`LiteBus.Transport.UnitTests` (`InMemory/`)
`PublishAsync_WhenDestinationIsFull_ShouldWaitForSettlement`	`LiteBus.Transport.UnitTests` (`InMemory/`)
`PublishAsync_WhenCapacityWaitIsCanceled_ShouldReleaseAdmissionWaiter`	`LiteBus.Transport.UnitTests` (`InMemory/`)
`Constructor_WithNonPositiveDestinationCapacity_ShouldThrow`	`LiteBus.Transport.UnitTests` (`InMemory/`)
`PublishThroughInMemoryTransport_ShouldAcceptProcessAndDispatchCommand`	`LiteBus.Durable.IntegrationTests` (`Ingress/InMemory/`)
`ProcessPendingAsync_ShouldPublishEnvelopeToInMemoryDestination`	`LiteBus.Durable.IntegrationTests` (`Dispatch/Outbox/InMemory/`)
`ProcessPendingAsync_ShouldPublishLeasedEnvelopeToInMemoryDestination`	`LiteBus.Durable.IntegrationTests` (`Dispatch/Inbox/InMemory/`)