Provider-agnostic event bus with schema validation, encryption, dead letter queues, and observability

A3S Event

A3S Event is a provider-agnostic event system for Rust. All backends implement the EventProvider trait — swap between NATS JetStream and in-memory without changing application code.

Feature Flags

All optional modules are behind feature gates. The minimal core compiles with zero optional dependencies.

Prop

Type

# Full (default)
a3s-event = "0.3"

# Minimal core only
a3s-event = { version = "0.3", default-features = false }

# Pick what you need
a3s-event = { version = "0.3", default-features = false, features = ["nats"] }

Architecture

┌──────────────────────────────────────────────────────────┐
│                        EventBus                          │
│                                                          │
│  ┌─────────────┐  ┌──────────────┐  ┌───────────────┐  │
│  │ SchemaReg   │  │  Encryptor   │  │  DLQ Handler  │  │
│  │ validate()  │  │ AES-256-GCM  │  │ MemoryDlq     │  │
│  └──────┬──────┘  └──────┬───────┘  └──────┬────────┘  │
│         │                │                  │            │
│         └────── publish ─┴── subscribe ─────┘            │
│                       │                                  │
│  ┌────────────────────┴────────────────────────────┐    │
│  │              EventProvider (trait)                │    │
│  │  publish · subscribe · durable · history · ack   │    │
│  └──────────────┬──────────────────┬───────────────┘    │
│                 │                  │                      │
│  ┌──────────────┴───┐  ┌──────────┴──────────┐         │
│  │  MemoryProvider   │  │   NatsProvider      │         │
│  │  tokio::broadcast │  │   JetStream         │         │
│  │  zero deps        │  │   durable subs      │         │
│  └──────────────────┘  └─────────────────────┘         │
│                                                          │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐  │
│  │ StateStore   │  │ EventMetrics │  │ Broker       │  │
│  │ File / Memory│  │ lock-free    │  │ routing ⚑    │  │
│  └──────────────┘  └──────────────┘  └──────────────┘  │
└──────────────────────────────────────────────────────────┘

⚑ = behind feature gate