FuseRule is both an executable binary that can be run, and a library that can be used in Rust programs.

Installing the command-line executable

Assuming you have Rust/Cargo installed, run this command in a terminal:

cargo install fuse-rule

It will make the fuse-rule command available in your PATH if you've allowed the PATH to be modified when installing Rust. cargo uninstall fuse-rule uninstalls.

Adding `fuse_rule` library as a dependency

Run this command in a terminal, in your project's directory:

cargo add fuse-rule

To add it manually, edit your project's Cargo.toml file and add to the [dependencies] section:

fuse-rule = "0.1.0"

The fuse_rule library will be automatically available globally. Read the fuse_rule library documentation.

Back to the crate overview.

Readme

FuseRule ⚡

FuseRule is a high-performance, developer-first rule engine built for the cloud-native ecosystem. It leverages Apache Arrow and DataFusion to provide a lightning-fast, SQL-expressive core for real-time data auditing and event processing.

Designed as an Infrastructure Primitive, FuseRule decouples its deterministic core from pluggable "edges" like persistence, evaluation engines, and notification agents.

🚀 Features

⚡ Arrow-Native: Zero-copy columnar data processing for maximum performance
🔍 SQL-Powered Rules: Write complex predicates using standard SQL expressions
🏗️ Infrastructure-First: Decoupled core with swappable traits for StateStore, RuleEvaluator, and Agent
📊 Real-Time Observability: Returns machine-readable EvaluationTrace logs for every ingestion
🔄 Zero-Downtime Reloading: Hot-swap rules and agents via SIGHUP without restarting the daemon
📈 Cloud-Native Metrics: Built-in Prometheus-formatted telemetry
🔔 Stateful Transitions: Built-in state management for Activated and Deactivated transitions
🪟 Time Windows: Sliding time windows for aggregate functions (AVG, COUNT, SUM)
🔐 API Key Authentication: Secure endpoints with configurable API keys
🚦 Rate Limiting: Built-in rate limiting for ingestion endpoints
📡 Multiple Ingestion Sources: HTTP, Kafka, and WebSocket support
🎨 Action Templates: Handlebars templating for custom webhook payloads
🐛 Interactive Debugging: REPL and step-through debugger for rule development

📦 Installation

As a Library

Add to your Cargo.toml:

[dependencies]
arrow-rule-agent = "0.1.0"

As a Binary

cargo install arrow-rule-agent

🎯 Quickstart

1. Create a Configuration File

Create fuse_rule_config.yaml:

engine:
  persistence_path: "fuserule_state"
  ingest_rate_limit: 1000  # requests per second
  api_keys:
    - "sk_live_abc123..."

schema:
  - name: "price"
    data_type: "float64"
  - name: "symbol"
    data_type: "utf8"
  - name: "volume"
    data_type: "int32"

agents:
  - name: "logger"
    type: "logger"
  - name: "slack-webhook"
    type: "webhook"
    url: "https://hooks.slack.com/services/YOUR/WEBHOOK/URL"
    template: |
      {
        "text": "🚨 {{rule_name}} triggered!",
        "symbol": "{{matched_data.0.symbol}}",
        "price": "{{matched_data.0.price}}"
      }

rules:
  - id: "high_price_alert"
    name: "High Price Alert"
    predicate: "price > 1000"
    action: "slack-webhook"
    version: 1
    enabled: true
    state_ttl_seconds: 3600  # Expire state after 1 hour

  - id: "volume_spike"
    name: "Volume Spike"
    predicate: "AVG(volume) > 10000"
    action: "logger"
    window_seconds: 60  # 60-second sliding window
    version: 1
    enabled: true

2. Start the Server

fuserule run --config fuse_rule_config.yaml --port 3030

3. Ingest Data

curl -X POST http://localhost:3030/ingest \
     -H "Content-Type: application/json" \
     -H "X-API-Key: sk_live_abc123..." \
     -d '[{"price": 1500, "symbol": "AAPL", "volume": 5000}]'

4. Check Rule States

# Get all rule states
curl http://localhost:3030/api/v1/state \
     -H "X-API-Key: sk_live_abc123..."

# Get specific rule state
curl http://localhost:3030/api/v1/state/high_price_alert \
     -H "X-API-Key: sk_live_abc123..."

📚 Usage as a Library

Basic Example

use arrow_rule_agent::{RuleEngine, config::FuseRuleConfig};
use arrow::array::{Float64Array, StringArray};
use arrow::datatypes::{DataType, Field, Schema};
use arrow::record_batch::RecordBatch;
use std::sync::Arc;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Load configuration
    let config = FuseRuleConfig::from_file("fuse_rule_config.yaml")?;
    
    // Create engine from config
    let mut engine = RuleEngine::from_config(config).await?;
    
    // Create a test batch
    let schema = Schema::new(vec![
        Field::new("price", DataType::Float64, true),
        Field::new("symbol", DataType::Utf8, true),
    ]);
    
    let price_array = Arc::new(Float64Array::from(vec![1500.0, 500.0]));
    let symbol_array = Arc::new(StringArray::from(vec!["AAPL", "GOOGL"]));
    
    let batch = RecordBatch::try_new(
        Arc::new(schema),
        vec![price_array, symbol_array],
    )?;
    
    // Process batch and get evaluation traces
    let traces = engine.process_batch(&batch).await?;
    
    for trace in traces {
        if trace.action_fired {
            println!("Rule '{}' activated!", trace.rule_name);
        }
    }
    
    Ok(())
}

Programmatic Rule Management

use arrow_rule_agent::{RuleEngine, rule::Rule};

// Add a rule programmatically
let rule = Rule {
    id: "custom_rule".to_string(),
    name: "Custom Rule".to_string(),
    predicate: "price > 100 AND volume < 50".to_string(),
    action: "logger".to_string(),
    window_seconds: None,
    version: 1,
    enabled: true,
};

engine.add_rule(rule).await?;

// Update a rule
engine.update_rule("custom_rule", updated_rule).await?;

// Toggle rule
engine.toggle_rule("custom_rule", false).await?;

🏗️ Architecture

┌─────────────────────────────────────────────────────────────┐
│                      FuseRule Engine                         │
├─────────────────────────────────────────────────────────────┤
│                                                               │
│  ┌──────────────┐    ┌──────────────┐    ┌──────────────┐ │
│  │   Ingest     │───▶│   Evaluate   │───▶│   Activate   │ │
│  │   Sources    │    │   Rules      │    │   Agents     │ │
│  └──────────────┘    └──────────────┘    └──────────────┘ │
│         │                   │                    │           │
│         │                   │                    │           │
│         ▼                   ▼                    ▼           │
│  ┌──────────────────────────────────────────────────────┐   │
│  │          Arrow RecordBatch (Zero-Copy)              │   │
│  └──────────────────────────────────────────────────────┘   │
│                                                               │
│  ┌──────────────┐    ┌──────────────┐    ┌──────────────┐ │
│  │   State      │    │   Windows     │    │   Metrics    │ │
│  │   Store      │    │   Buffers     │    │   (Prom)     │ │
│  └──────────────┘    └──────────────┘    └──────────────┘ │
└─────────────────────────────────────────────────────────────┘

Design Philosophy: "Hard Core, Soft Edges"

FuseRule is built on the philosophy that the core logic of a rule engine should be a "boring," deterministic primitive, while the integration points (Ingress, Persistence, Notifications) should be flexible and pluggable.

Core (Hard):

Rule evaluation logic
State transitions
Window management
Metrics collection

Edges (Soft):

StateStore trait (Sled, Redis, etc.)
RuleEvaluator trait (DataFusion, custom SQL engines)
Agent trait (Webhooks, Loggers, custom actions)
Ingestion sources (HTTP, Kafka, WebSocket)

🔧 CLI Commands

Run Server

fuserule run --config fuse_rule_config.yaml --port 3030

Validate Rules

# Validate all rules in config
fuserule validate --config fuse_rule_config.yaml

# Validate specific predicate
fuserule validate --config fuse_rule_config.yaml --predicate "price > 100"

Interactive REPL

fuserule repl --config fuse_rule_config.yaml

Rule Debugger

fuserule debug --config fuse_rule_config.yaml

📡 API Endpoints

Public Endpoints

GET /status - Server status
GET /health - Health check with engine stats
GET /metrics - Prometheus metrics

Protected Endpoints (Require `X-API-Key` header)

Rule Management

GET /rules - List all rules
POST /api/v1/rules - Create new rule
PUT /api/v1/rules/:id - Update rule
PATCH /api/v1/rules/:id - Partial update (e.g., enable/disable)
DELETE /api/v1/rules/:id - Delete rule
POST /api/v1/rules/validate - Validate rule predicate

State Management

GET /api/v1/state - Get all rule states
GET /api/v1/state/:rule_id - Get specific rule state

Data Ingestion

POST /ingest - Ingest JSON data (rate-limited)

📊 Monitoring

FuseRule exposes Prometheus metrics at /metrics:

fuserule_batches_processed_total - Total batches ingested
fuserule_activations_total - Total rule activations
fuserule_agent_failures_total - Total agent failures
fuserule_evaluation_duration_seconds - Evaluation latency histogram
fuserule_rule_evaluations_total{rule_id} - Per-rule evaluation count
fuserule_rule_activations_total{rule_id} - Per-rule activation count

🔌 Ingestion Sources

HTTP (Default)

curl -X POST http://localhost:3030/ingest \
     -H "Content-Type: application/json" \
     -d '[{"price": 150, "symbol": "AAPL"}]'

Kafka

Configure in fuse_rule_config.yaml:

sources:
  - type: "kafka"
    brokers: ["localhost:9092"]
    topic: "events"
    group_id: "fuserule"
    auto_commit: true

WebSocket

Configure in fuse_rule_config.yaml:

sources:
  - type: "websocket"
    bind: "0.0.0.0:3031"
    max_connections: 1000

Connect and send JSON:

const ws = new WebSocket('ws://localhost:3031/ws');
ws.send(JSON.stringify([{"price": 150, "symbol": "AAPL"}]));

🎨 Action Templates

Use Handlebars templates for custom webhook payloads:

agents:
  - name: "custom-webhook"
    type: "webhook"
    url: "https://api.example.com/webhook"
    template: |
      {
        "alert": "{{rule_name}}",
        "timestamp": "{{timestamp}}",
        "data": {{#each matched_data}}
          {
            "price": {{price}},
            "symbol": "{{symbol}}"
          }{{#unless @last}},{{/unless}}
        {{/each}},
        "count": {{count}}
      }

🧪 Testing

Unit Tests

cargo test --test unit_test

Integration Tests

cargo test --test integration_test

Property-Based Tests

cargo test --test property_test

📖 Documentation

Architecture Guide - Deep dive into design
API Documentation - Full API reference (when published)
Local API Documentation: Generate and view locally with:
```
cargo doc --no-deps --open
```
This will build and open the documentation in your browser at target/doc/arrow_rule_agent/index.html
Examples - Code examples

🤝 Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

📜 License

Licensed under the Apache License, Version 2.0. See LICENSE for details.

🙏 Acknowledgments

Built on Apache Arrow for zero-copy data processing
Powered by DataFusion for SQL evaluation
Inspired by the "Hard Core, Soft Edges" philosophy

Installing the command-line executable

Adding fuse_rule library as a dependency

Adding `fuse_rule` library as a dependency