Module nats 

NATS provider implementation using JetStream.

This module provides production-ready NATS integration via the async-nats client with JetStream. It implements the QueueProvider and SessionProvider traits, enabling NATS to be used as a drop-in backend in the queue-runtime abstraction layer.

Key Features

• JetStream: Persistent, at-least-once message delivery with ack/nak semantics
• Pull consumers: Explicit message fetch with configurable ack-wait (visibility timeout analog)
• Dead letter support: Failed messages forwarded to a configurable DLQ stream
• Session emulation: Sessions emulated via per-session filter subjects within a shared stream
• Batch operations: Up to 100 messages per batch

Stream and Subject Naming

The provider creates one JetStream stream per queue. Naming conventions:

• Stream name: {stream_prefix}-{queue_name} (hyphens replace underscores for NATS compatibility)
• Subject: {stream_prefix}.{queue_name}
• Session subject: {stream_prefix}.{queue_name}.session.{session_id}

Dead Letter Support

When enable_dead_letter is true and dead_letter_subject_prefix is set, messages dead-lettered via [dead_letter_message] are published to {prefix}.{queue_name} using a separate JetStream stream for DLQ messages.

Session Support

Sessions are emulated via JetStream subject filtering. Each session gets its own subject ({prefix}.{queue}.session.{session_id}), and a NatsSessionProvider creates a per-session pull consumer filtered to that subject.

Connection

The provider uses the async-nats client which reconnects automatically on connection loss. Optional NATS credentials can be loaded from a .creds file via the credentials_path configuration field.

Testing

use queue_runtime::providers::NatsProvider;
use queue_runtime::NatsConfig;

let config = NatsConfig {
    url: "nats://localhost:4222".to_string(),
    ..NatsConfig::default()
};

let provider = NatsProvider::new(config).await.unwrap();

Structs

NatsConfig

NATS provider configuration using JetStream

NatsError

NATS-specific error type.

NatsProvider

NATS queue provider using JetStream for persistent, at-least-once delivery.

NatsSessionProvider

Session provider for NATS using a per-session JetStream pull consumer.