Version: 1.0.0

Middleware

Add custom middleware for logging, metrics, distributed tracing, and other cross-cutting concerns.

Basic Middleware

fn logging(_payload: &[u8], result: &Result<()>) -> Result<()> {
    match result {
        Ok(_) => tracing::info!("✓ Message processed successfully"),
        Err(e) => tracing::error!("✗ Message processing failed: {:?}", e),
    }
    Ok(())
}

WorkerBuilder::new(ExchangeKind::Direct)
    .pool(pool)
    .queue("order.process")
    .middleware(logging)
    .build(handler)

Middleware Function Signature

fn middleware(
    payload: &[u8],
    result: &Result<()>,
) -> Result<()>

Parameters:

payload: Raw message bytes
result: Result of handler execution

Returns:

Ok(()): Continue processing
Err(_): Stop processing (optional)

Execution Order

Message Arrives
    ↓
Before Middleware (if implemented)
    ↓
Handler Function
    ↓
After Middleware (current)
    ↓
Ack/Nack Message

Built-in Middleware

Logging Middleware

pub fn logging(_payload: &[u8], result: &Result<()>) -> Result<()> {
    match result {
        Ok(_) => tracing::info!("✓ Message processed successfully"),
        Err(e) => tracing::error!("✗ Message processing failed: {:?}", e),
    }
    Ok(())
}

Usage:

.middleware(logging)

Metrics Middleware

pub fn metrics(_payload: &[u8], result: &Result<()>) -> Result<()> {
    static SUCCESS_COUNT: AtomicU64 = AtomicU64::new(0);
    static ERROR_COUNT: AtomicU64 = AtomicU64::new(0);
    
    match result {
        Ok(_) => {
            let count = SUCCESS_COUNT.fetch_add(1, Ordering::Relaxed);
            tracing::info!("📊 Success count: {}", count + 1);
        }
        Err(_) => {
            let count = ERROR_COUNT.fetch_add(1, Ordering::Relaxed);
            tracing::warn!("📊 Error count: {}", count + 1);
        }
    }
    Ok(())
}

Usage:

.middleware(metrics)

Tracing Middleware

pub fn tracing(_payload: &[u8], result: &Result<()>) -> Result<()> {
    let trace_id = extract_trace_id()
        .unwrap_or_else(|| "unknown".to_string());
    
    match result {
        Ok(_) => tracing::info!("✓ Processed - trace-id: {}", trace_id),
        Err(e) => tracing::warn!("✗ Failed - trace-id: {} | error: {:?}", trace_id, e),
    }
    Ok(())
}

fn extract_trace_id() -> Option<String> {
    easy_rmq::get_headers()
        .and_then(|h| h.inner().get("x-trace-id").cloned())
        .and_then(|v| match v {
            lapin::types::AMQPValue::LongString(s) => Some(s.to_string()),
            lapin::types::AMQPValue::ShortString(s) => Some(s.to_string()),
            _ => None,
        })
}

Usage:

.middleware(tracing)

Custom Middleware

Timing Middleware

fn timing(payload: &[u8], result: &Result<()>) -> Result<()> {
    use std::time::Instant;
    
    thread_local! {
        static START_TIME: RefCell<Option<Instant>> = RefCell::new(None);
    }
    
    // Before handler
    if result.is_ok() {
        START_TIME.with(|start| {
            *start.borrow_mut() = Some(Instant::now());
        });
    }
    
    // After handler
    if let Ok(_) = result {
        START_TIME.with(|start| {
            if let Some(start_time) = start.borrow().as_ref() {
                let duration = start_time.elapsed();
                tracing::info!("⏱️ Processing time: {:?}", duration);
            }
        });
    }
    
    Ok(())
}

Validation Middleware

fn validation(payload: &[u8], _result: &Result<()>) -> Result<()> {
    // Validate message size
    if payload.len() > 1_000_000 {
        tracing::error!("Message too large: {} bytes", payload.len());
        return Err(easy_rmq::Error::Custom("Message too large".into()));
    }
    
    // Validate JSON structure
    if let Err(e) = serde_json::from_slice::<serde_json::Value>(payload) {
        tracing::error!("Invalid JSON: {:?}", e);
        return Err(easy_rmq::Error::Custom(format!("Invalid JSON: {}", e)));
    }
    
    Ok(())
}

Enrichment Middleware

fn enrichment(payload: &[u8], result: &Result<()>) -> Result<()> {
    if let Ok(msg) = serde_json::from_slice::<Value>(payload) {
        // Add metadata
        let enriched = json!({
            "data": msg,
            "processed_at": Utc::now().to_rfc3339(),
            "consumer_id": get_consumer_id(),
        });
        
        tracing::debug!("Enriched message: {}", enriched);
    }
    
    Ok(())
}

Rate Limiting Middleware

fn rate_limiter(payload: &[u8], result: &Result<()>) -> Result<()> {
    use std::sync::atomic::{AtomicU64, Ordering};
    
    static COUNTER: AtomicU64 = AtomicU64::new(0);
    static LAST_RESET: AtomicU64 = AtomicU64::new(0);
    
    let now = Utc::now().timestamp() as u64;
    let last_reset = LAST_RESET.load(Ordering::Relaxed);
    
    // Reset counter every minute
    if now - last_reset > 60 {
        COUNTER.store(0, Ordering::Relaxed);
        LAST_RESET.store(now, Ordering::Relaxed);
    }
    
    let count = COUNTER.fetch_add(1, Ordering::Relaxed);
    
    if count > 1000 {
        tracing::warn!("Rate limit exceeded: {} messages/min", count);
        return Err(easy_rmq::Error::Custom("Rate limit exceeded".into()));
    }
    
    Ok(())
}

Chaining Middleware

WorkerBuilder::new(ExchangeKind::Direct)
    .pool(pool)
    .queue("order.process")
    .middleware(validation)     // 1. Validate message
    .middleware(rate_limiter)   // 2. Check rate limit
    .middleware(tracing)        // 3. Log trace ID
    .middleware(timing)         // 4. Measure time
    .middleware(metrics)        // 5. Track metrics
    .middleware(logging)        // 6. Log result
    .build(handler)

Execution Order:

Validation
Rate limiting
Tracing
Timing
Metrics
Logging

Complete Example

use easy_rmq::{AmqpClient, SubscriberRegistry, WorkerBuilder};
use lapin::ExchangeKind;

#[tokio::main]
async fn main() -> easy_rmq::Result<()> {
    let client = AmqpClient::new("amqp://guest:guest@localhost:5672".to_string(), 10)?;
    let pool = client.channel_pool();

    let worker = SubscriberRegistry::new()
        .register({
            let pool = pool.clone();
            move |_count| {
                WorkerBuilder::new(ExchangeKind::Direct)
                    .pool(pool)
                    .with_exchange("orders")
                    .queue("order.process")
                    .retry(3, 5000)
                    .prefetch(50)
                    .concurrency(10)
                    .parallelize(tokio::task::spawn)
                    .middleware(validation)
                    .middleware(tracing)
                    .middleware(timing)
                    .middleware(metrics)
                    .middleware(logging)
                    .build(handle_order)
            }
        });

    worker.run().await?;
    Ok(())
}

fn validation(payload: &[u8], _result: &Result<()>) -> easy_rmq::Result<()> {
    if payload.len() > 1_000_000 {
        return Err(easy_rmq::Error::Custom("Message too large".into()));
    }
    Ok(())
}

fn tracing(_payload: &[u8], result: &Result<()>) -> easy_rmq::Result<()> {
    let trace_id = extract_trace_id().unwrap_or_else(|| "unknown".to_string());
    match result {
        Ok(_) => tracing::info!("✓ Processed - trace-id: {}", trace_id),
        Err(e) => tracing::warn!("✗ Failed - trace-id: {} | error: {:?}", trace_id, e),
    }
    Ok(())
}

fn timing(_payload: &[u8], result: &Result<()>) -> easy_rmq::Result<()> {
    use std::time::Instant;
    thread_local! {
        static START_TIME: RefCell<Option<Instant>> = RefCell::new(None);
    }
    
    if result.is_ok() {
        START_TIME.with(|start| *start.borrow_mut() = Some(Instant::now()));
    } else {
        START_TIME.with(|start| {
            if let Some(start_time) = start.borrow().as_ref() {
                let duration = start_time.elapsed();
                tracing::info!("⏱️ Processing time: {:?}", duration);
            }
        });
    }
    Ok(())
}

fn metrics(_payload: &[u8], result: &Result<()>) -> easy_rmq::Result<()> {
    static SUCCESS_COUNT: AtomicU64 = AtomicU64::new(0);
    static ERROR_COUNT: AtomicU64 = AtomicU64::new(0);
    
    match result {
        Ok(_) => {
            let count = SUCCESS_COUNT.fetch_add(1, Ordering::Relaxed);
            tracing::info!("📊 Success: {}", count + 1);
        }
        Err(_) => {
            let count = ERROR_COUNT.fetch_add(1, Ordering::Relaxed);
            tracing::warn!("📊 Error: {}", count + 1);
        }
    }
    Ok(())
}

fn logging(_payload: &[u8], result: &Result<()>) -> easy_rmq::Result<()> {
    match result {
        Ok(_) => tracing::info!("✓ Message processed"),
        Err(e) => tracing::error!("✗ Message failed: {:?}", e),
    }
    Ok(())
}

fn handle_order(data: Vec<u8>) -> easy_rmq::Result<()> {
    let order: Order = serde_json::from_slice(&data)?;
    // Process order
    Ok(())
}

Best Practices

Keep middleware simple: Each middleware should do one thing
Order matters: Place validation before expensive operations
Don't swallow errors: Let errors propagate for retry
Use thread-local storage: For before/after state
Monitor overhead: Middleware adds latency, measure it
Test middleware: Test middleware independently

Common Patterns

Circuit Breaker

fn circuit_breaker(payload: &[u8], result: &Result<()>) -> Result<()> {
    static FAILURE_COUNT: AtomicU64 = AtomicU64::new(0);
    static LAST_FAILURE: AtomicU64 = AtomicU64::new(0);
    
    let now = Utc::now().timestamp() as u64;
    let failures = FAILURE_COUNT.load(Ordering::Relaxed);
    
    // Check if circuit is open
    if failures > 10 {
        let last_failure = LAST_FAILURE.load(Ordering::Relaxed);
        if now - last_failure < 60 {
            return Err(easy_rmq::Error::Custom("Circuit breaker open".into()));
        } else {
            // Reset circuit breaker
            FAILURE_COUNT.store(0, Ordering::Relaxed);
        }
    }
    
    // Track failures
    if result.is_err() {
        FAILURE_COUNT.fetch_add(1, Ordering::Relaxed);
        LAST_FAILURE.store(now, Ordering::Relaxed);
    }
    
    Ok(())
}

Dead Letter Queue

fn dead_letter(payload: &[u8], result: &Result<()>) -> Result<()> {
    if let Err(e) = result {
        tracing::error!("Message failed, sending to DLQ: {:?}", e);
        
        // Send to dead letter queue
        let client = get_dlq_client()?;
        client.publisher()
            .publish_text("dlq", String::from_utf8_lossy(payload))
            .await?;
    }
    
    Ok(())
}

What's Next

Distributed Tracing - Advanced tracing patterns
Retry Mechanism - Handle failed messages
Prefetch Control - Optimize message buffering

Basic Middleware​

Middleware Function Signature​

Execution Order​

Built-in Middleware​

Logging Middleware​

Metrics Middleware​

Tracing Middleware​

Custom Middleware​

Timing Middleware​

Validation Middleware​

Enrichment Middleware​

Rate Limiting Middleware​

Chaining Middleware​

Complete Example​

Best Practices​

Common Patterns​

Circuit Breaker​

Dead Letter Queue​

What's Next​

Basic Middleware

Middleware Function Signature

Execution Order

Built-in Middleware

Logging Middleware

Metrics Middleware

Tracing Middleware

Custom Middleware

Timing Middleware

Validation Middleware

Enrichment Middleware

Rate Limiting Middleware

Chaining Middleware

Complete Example

Best Practices

Common Patterns

Circuit Breaker

Dead Letter Queue

What's Next