systemprompt-events 0.32.2

Event bus, SSE broadcasters, and fan-out routing for systemprompt.io AI governance infrastructure. A2A, analytics, and context stream wiring for the MCP governance pipeline.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155

<div align="center">

<picture>
  <source media="(prefers-color-scheme: dark)" srcset="https://systemprompt.io/files/images/logo.svg">
  <source media="(prefers-color-scheme: light)" srcset="https://systemprompt.io/files/images/logo-dark.svg">
  <img src="https://systemprompt.io/files/images/logo.svg" alt="systemprompt.io" width="180">
</picture>

### Production infrastructure for AI agents

[**Website**](https://systemprompt.io) · [**Documentation**](https://systemprompt.io/documentation/) · [**Guides**](https://systemprompt.io/guides) · [**Core**](https://github.com/systempromptio/systemprompt-core) · [**Template**](https://github.com/systempromptio/systemprompt-template) · [**Discord**](https://discord.gg/wkAbSuPWpr)

</div>

---

# systemprompt-events

<div align="center">
  <picture>
    <source media="(prefers-color-scheme: dark)" srcset="https://raw.githubusercontent.com/systempromptio/systemprompt-core/main/assets/readme/terminals/dark/00-overview.svg">
    <source media="(prefers-color-scheme: light)" srcset="https://raw.githubusercontent.com/systempromptio/systemprompt-core/main/assets/readme/terminals/light/00-overview.svg">
    <img alt="systemprompt-events — systemprompt-core workspace" src="https://raw.githubusercontent.com/systempromptio/systemprompt-core/main/assets/readme/terminals/dark/00-overview.svg" width="100%">
  </picture>
</div>

[![Crates.io](https://img.shields.io/crates/v/systemprompt-events.svg?style=flat-square)](https://crates.io/crates/systemprompt-events)
[![Docs.rs](https://img.shields.io/docsrs/systemprompt-events?style=flat-square)](https://docs.rs/systemprompt-events)
[![codecov](https://img.shields.io/codecov/c/github/systempromptio/systemprompt-core/main?style=flat-square&logo=codecov)](https://codecov.io/gh/systempromptio/systemprompt-core)
[![License: BSL-1.1](https://img.shields.io/badge/license-BSL--1.1-2b6cb0?style=flat-square)](https://github.com/systempromptio/systemprompt-core/blob/main/LICENSE)

Every A2A, AG-UI, analytics, and context event fans out through one bus, and a durable Postgres outbox carries it across replicas so nothing is lost to a restart. Any component holding a `UserId` can publish without touching the wire format.

**Layer**: Infra. Infrastructure primitives consumed by the domain and application crates. Part of the [systemprompt-core](https://github.com/systempromptio/systemprompt-core) workspace.

## What it does

The in-process event bus fans typed events out to per-user SSE connections, managing connection lifecycles and cleaning up disconnected clients. It is not SSE-only: a durable Postgres outbox (`event_outbox` table, via LISTEN/NOTIFY) relays events across replicas so a multi-instance deployment stays consistent. The crate is shared between the HTTP API entry crate and the runtime layer.

## Modules

| Module | Purpose |
|--------|---------|
| `services` | The `GenericBroadcaster` implementation and per-event aliases, the static `EventRouter`, `ConnectionGuard`, keep-alive utilities, the `PostgresEventBridge` (LISTEN/NOTIFY relay), and the outbox repository. |
| `sse` | The `ToSse` trait and `serde`-driven impls converting `systemprompt-models` event types into `axum` SSE records. |
| `extension` | `EventsExtension` declares the `event_outbox` schema through the workspace extension framework. |
| `error` | `EventError` / `EventResult`. |

Schema DDL lives in `schema/` (`event_outbox.sql` plus the `migrations/` directory).

### Event flow

```
                    ┌─────────────────┐
                    │   EventRouter   │
                    └────────┬────────┘
                             │
        ┌────────────────────┼────────────────────┐
        │                    │                    │
        ▼                    ▼                    ▼
┌───────────────┐    ┌───────────────┐    ┌───────────────────┐
│AGUI_BROADCASTER│    │A2A_BROADCASTER│    │CONTEXT_BROADCASTER│
└───────┬───────┘    └───────┬───────┘    └─────────┬─────────┘
        │                    │                      │
        ▼                    ▼                      ▼
   SSE Clients          SSE Clients            SSE Clients
```

AG-UI and A2A events route to both their primary broadcaster and the context broadcaster for aggregation. Across replicas, `PostgresEventBridge` relays outbox rows so an instance publishes locally and every other instance sees it.

## Usage

```toml
[dependencies]
systemprompt-events = "0.32"
```

```rust
use systemprompt_events::{AGUI_BROADCASTER, Broadcaster};
use systemprompt_identifiers::UserId;

async fn active_listeners(user_id: &UserId) -> usize {
    AGUI_BROADCASTER.connection_count(user_id).await
}
```

## Public API

### Traits
| Trait | Methods | Purpose |
|-------|---------|---------|
| `Broadcaster` | `register`, `unregister`, `broadcast`, `connection_count`, `total_connections` | Type-safe event broadcasting |

### Types
| Type | Description |
|------|-------------|
| `EventSender` | `tokio::sync::mpsc::Sender<Result<Event, Infallible>>` |
| `EventError` / `EventResult<T>` | `thiserror`-derived error and result alias |
| `GenericBroadcaster<E>` | Generic broadcaster for any `ToSse + Clone + Send + Sync` event |
| `AgUiBroadcaster` | `GenericBroadcaster<AgUiEvent>` |
| `A2ABroadcaster` | `GenericBroadcaster<A2AEvent>` |
| `ContextBroadcaster` | `GenericBroadcaster<ContextEvent>` |
| `AnalyticsBroadcaster` | `GenericBroadcaster<AnalyticsEvent>` |
| `ConnectionGuard<E>` | RAII guard for automatic unregistration |
| `EventRouter` | Routes events to appropriate broadcasters |
| `PostgresEventBridge` | LISTEN/NOTIFY relay draining the `event_outbox` table across replicas |
| `OutboxChannel` / `OUTBOX_CHANNEL` | Outbox notification channel type and name |
| `EventsExtension` | Extension registering the `event_outbox` schema |

### Constants
| Constant | Value | Purpose |
|----------|-------|---------|
| `HEARTBEAT_INTERVAL` | 15 seconds | SSE keep-alive interval |
| `HEARTBEAT_JSON` | `{"type":"heartbeat"}` | Keep-alive payload |

### Global Singletons
| Static | Type | Purpose |
|--------|------|---------|
| `AGUI_BROADCASTER` | `LazyLock<AgUiBroadcaster>` | AG-UI event broadcasts |
| `A2A_BROADCASTER` | `LazyLock<A2ABroadcaster>` | Agent-to-agent events |
| `CONTEXT_BROADCASTER` | `LazyLock<ContextBroadcaster>` | Aggregated context events |
| `ANALYTICS_BROADCASTER` | `LazyLock<AnalyticsBroadcaster>` | Analytics event tracking |

## Tests

Tests are located in `crates/tests/unit/infra/events/` following the project convention of separating tests from source files.

## Dependencies

| Crate | Purpose |
|-------|---------|
| `systemprompt-models` | Event types (`AgUiEvent`, `A2AEvent`, `ContextEvent`, `SystemEvent`, `AnalyticsEvent`) |
| `systemprompt-identifiers` | `UserId` / `ConnectionId` types (`sqlx` feature) |
| `systemprompt-extension` | Schema registration for the `event_outbox` table |
| `tokio` | Async runtime, channels, synchronization |
| `axum` | SSE `Event` and `KeepAlive` types |
| `sqlx` | Durable outbox relay over Postgres LISTEN/NOTIFY |
| `chrono` | Outbox row timestamps |
| `inventory` | Compile-time extension registration |
| `serde` / `serde_json` | Event serialization |
| `tracing` | Structured logging |

## License

BSL-1.1 (Business Source License). Source-available for evaluation, testing, and non-production use. Production use requires a commercial license. Each version converts to Apache 2.0 four years after publication. See [LICENSE](https://github.com/systempromptio/systemprompt-core/blob/main/LICENSE).

---

<div align="center">

**[systemprompt.io](https://systemprompt.io)** · **[Documentation](https://systemprompt.io/documentation/)** · **[Guides](https://systemprompt.io/guides)** · **[Live Demo](https://systemprompt.io/features/demo)** · **[Template](https://github.com/systempromptio/systemprompt-template)** · **[crates.io](https://crates.io/crates/systemprompt-events)** · **[docs.rs](https://docs.rs/systemprompt-events)** · **[Discord](https://discord.gg/wkAbSuPWpr)**

<sub>Infra layer · Own how your organization uses AI.</sub>

</div>