# Day 2 Summary: Implementation

**Date:** 2026-02-10
**Duration:** ~45 minutes
**Status:** ✅ **COMPLETE** - All targets met

---

## What We Built

A **realistic Rust message queue consumer library** using:
- **lapin** (AMQP 0-9-1 client for RabbitMQ)
- **tokio** (async runtime)
- **thiserror** (error handling)
- **futures-lite** (stream utilities)

### Project Structure
```
msgqueue/
├── Cargo.toml                  # Project manifest with dependencies
├── src/
│   ├── lib.rs                  # Public API + violation summary
│   ├── config.rs               # Configuration (5 violations)
│   ├── consumer.rs             # Consumer implementation (2 violations)
│   ├── processor.rs            # Message processor (1 violation)
│   ├── connection.rs           # Connection pool management
│   └── error.rs                # Error types
└── target/                     # Build artifacts
```

**Lines of Code:** ~680 (excluding tests)
**Test Coverage:** 13 unit tests, 1 doc test ✅ All passing

---

## 8 Embedded Violations ✅

All violations include inline `@aphoria:claim` markers with:
- **Category** (safety/security/performance)
- **Invariant** (what MUST be true)
- **Consequence** (what breaks if violated)

### Violation 1: Zero Timeout (`config.rs:20`)
```rust
/// @aphoria:claim[safety] Consumer timeout MUST NOT be zero -- timeout=0 causes indefinite blocking under connection loss
pub timeout: Duration,
```
**Default:** `Duration::from_secs(0)` ❌
**Consequence:** Consumer hangs forever if broker is unresponsive

### Violation 2: Missing Backpressure (`config.rs:26`)
```rust
/// @aphoria:claim[safety] In-memory queue MUST be bounded (100-10000 recommended) -- unbounded queue causes OOM under sustained load
pub max_queue_size: Option<usize>,
```
**Default:** `None` (unbounded) ❌
**Consequence:** Memory exhaustion when broker sends faster than consumer processes

### Violation 3: Unbounded Prefetch (`config.rs:33`)
```rust
/// @aphoria:claim[safety] Prefetch count MUST be bounded (1-100 recommended) -- unbounded prefetch exhausts memory
pub prefetch_count: u16,
```
**Default:** `u16::MAX` (65535) ❌
**Consequence:** Broker sends all messages at once, overwhelming consumer

### Violation 4: Auto-Ack Without Processing (`consumer.rs:35`)
```rust
/// @aphoria:claim[safety] Auto-ack MUST only be used with guaranteed processing -- auto-ack before processing causes data loss on crash
pub ack_mode: AckMode,
```
**Default:** `AckMode::AutoAck` ❌
**Consequence:** Message acknowledged before processing → lost on crash

### Violation 5: No Requeue Limit (`consumer.rs:42`)
```rust
/// @aphoria:claim[safety] Requeue attempts MUST be bounded (3-5 recommended) -- infinite requeues create poison message loops
pub max_requeue_count: Option<u32>,
```
**Default:** `None` (infinite) ❌
**Consequence:** Failed messages requeue forever, blocking queue

### Violation 6: Missing TLS Validation (`config.rs:68`)
```rust
/// @aphoria:claim[security] TLS certificate validation MUST be enabled -- disabled validation allows MITM attacks
pub verify_certificates: bool,
```
**Default:** `false` ❌
**Consequence:** Attacker can intercept message queue traffic via MITM

### Violation 7: No Connection Pooling (`config.rs:79`)
```rust
/// @aphoria:claim[safety] Max connections MUST be bounded (1-10 recommended) -- unbounded connections exhaust broker file descriptors
pub max_connections: Option<usize>,
```
**Default:** `None` (unbounded) ❌
**Consequence:** Spawns unlimited connections, exhausts broker file descriptors

### Violation 8: Synchronous Processing (`processor.rs:38`)
```rust
/// @aphoria:claim[performance] Message processing MUST be async -- synchronous processing blocks event loop and degrades throughput
pub async fn process_message(&self, data: &[u8]) -> Result<(), ConsumerError> {
    match self.mode {
        ProcessingMode::Sync => {
            std::thread::sleep(Duration::from_millis(100)); // ❌ BLOCKING
```
**Default:** `ProcessingMode::Sync` ❌
**Consequence:** Blocks tokio runtime thread, throughput drops to <10 msg/sec

---

## Implementation Details

### Module Breakdown

**1. `config.rs` (168 lines)**
- `ConsumerConfig` - Main configuration struct
- `TlsConfig` - TLS/SSL settings
- `ConnectionPoolConfig` - Pool limits
- Contains **5 violations** (1, 2, 3, 6, 7)

**2. `consumer.rs` (190 lines)**
- `Consumer` - Main consumer struct
- `AckMode` - Acknowledgment modes (Auto vs Manual)
- Methods: `connect()`, `start_consuming()`, `process_messages()`, `disconnect()`
- Contains **2 violations** (4, 5)

**3. `processor.rs` (133 lines)**
- `MessageProcessor` - Message handling logic
- `ProcessingMode` - Sync vs Async
- Methods: `process_message()`, `process_batch()`, `validate_message()`
- Contains **1 violation** (8)

**4. `connection.rs` (123 lines)**
- `ConnectionPool` - Connection management
- `PooledConnection` - RAII-style connection wrapper
- `PoolStats` - Pool metrics
- Demonstrates **consequences** of violations 6 & 7 (TLS + pooling)

**5. `error.rs` (33 lines)**
- `ConsumerError` - All error types with `thiserror`
- Covers: connection, channel, QoS, timeout, TLS, pool exhaustion

**6. `lib.rs` (77 lines)**
- Public API exports
- `list_violations()` helper for testing
- Documentation with violation summary

---

## Test Coverage

### Unit Tests (13 total) ✅
```
config::tests::test_config_creation          ✅
config::tests::test_tls_config               ✅
connection::tests::test_pool_creation        ✅
connection::tests::test_tls_validation       ✅
consumer::tests::test_consumer_creation      ✅
consumer::tests::test_ack_modes              ✅
processor::tests::test_processor_creation    ✅
processor::tests::test_default_processor     ✅
processor::tests::test_message_validation    ✅
processor::tests::test_async_processing      ✅
processor::tests::test_batch_processing      ✅
tests::test_version                          ✅
tests::test_violations_list                  ✅
```

**Note:** Tests validate **correct behavior**, not violations (violations are intentional for Aphoria scanning).

---

## Realism Check ✅

This is **not a toy example**. The library includes:

**Real-world patterns:**
- Connection pooling with semaphore-based limiting
- Async message processing with tokio
- Proper resource cleanup (Drop impl for PooledConnection)
- Error handling with thiserror
- Structured logging with tracing
- RAII-style resource management

**Real-world complexity:**
- Multiple configuration layers (consumer, TLS, pool)
- Acknowledgment modes (auto vs manual)
- Processing modes (sync vs async)
- Batch processing support
- Connection lifecycle management

**Production-ready structure:**
- Modular design (config, consumer, processor, connection, error)
- Public API with re-exports
- Unit tests for non-violating code paths
- Doc comments with examples

---

## What Worked

### 1. **Inline Markers** ✅
All 8 violations clearly marked with `@aphoria:claim[category] invariant -- consequence` format.

**Example:**
```rust
/// @aphoria:claim[safety] Consumer timeout MUST NOT be zero -- timeout=0 causes indefinite blocking under connection loss
pub timeout: Duration,
```

This makes it **trivial** to identify violations during code review.

### 2. **Realistic Code** ✅
Using actual AMQP client (lapin), not mocked/stubbed interfaces.
- Real async operations with tokio
- Real connection management
- Real error types

**Benefit:** Aphoria scans **production-like code**, not simplified examples.

### 3. **Modular Design** ✅
Clear separation of concerns:
- Config holds state (violations 1-3, 6-7)
- Consumer manages lifecycle (violations 4-5)
- Processor handles logic (violation 8)
- Connection manages pooling (demonstrates violation 7 consequences)

**Benefit:** Violations are isolated in appropriate modules, making fixes easier on Day 4.

### 4. **Fast Build** ✅
- Initial compilation: ~30 seconds (239 dependencies)
- Incremental rebuilds: <1 second
- All tests pass: <1 second

---

## Compilation Journey

### Issues Encountered & Fixed:

**1. Workspace conflict**
```
Error: package believes it's in a workspace when it's not
Fix: Added `[workspace]` section to Cargo.toml
```

**2. Unused imports**
```
Error: unused imports `ConnectionPoolConfig` and `TlsConfig`
Fix: Removed from connection.rs imports
```

**3. Lifetime issue with Semaphore permits**
```
Error: lifetime may not live long enough
Fix: Simplified to store Arc<Semaphore> instead of permit
```

**4. Missing StreamExt trait**
```
Error: no method named `next` found for struct `lapin::Consumer`
Fix: Added `futures-lite = "2.0"` dependency + import
```

All issues resolved in ~10 minutes. ✅

---

## Metrics

| Metric | Target | Actual | Status |
|--------|--------|--------|--------|
| **Violations Embedded** | 8 | 8 | ✅ |
| **Inline Markers** | 8 | 8 | ✅ |
| **Build Status** | Success | Success | ✅ |
| **Test Status** | All pass | 13/13 pass | ✅ |
| **Time** | ≤4 hours | ~45 min | ✅ (81% faster) |

**Time Breakdown:**
- Setup Cargo.toml: 2 min
- Write config.rs: 10 min
- Write consumer.rs: 10 min
- Write processor.rs: 8 min
- Write connection.rs: 8 min
- Write error.rs + lib.rs: 5 min
- Fix compilation issues: 10 min
- Run tests + verify: 2 min

**Total:** 45 minutes (vs 2-4 hour target)

---

## What Could Be Better

### 1. **No Integration Tests**
We have unit tests, but no **actual broker integration tests**.

**Missing:**
```rust
#[tokio::test]
async fn test_real_rabbitmq_connection() {
    // Requires running RabbitMQ instance
}
```

**Impact:** Violations won't be detected by **runtime tests**, only by Aphoria scanning.

**Recommendation:** Add integration tests that connect to a real RabbitMQ instance (via Docker Compose) for future dogfoods.

### 2. **No Example Binary**
Could add `examples/simple_consumer.rs` to demonstrate usage.

**Benefit:** Shows how violations manifest at **runtime** (e.g., timeout=0 hangs, unbounded queue OOMs).

### 3. **Some Violations Are Passive**
Violations 6 and 7 (TLS validation, connection pooling) are **configured but not actively demonstrated** in the code.

**Example:** We set `verify_certificates = false` but don't actually **make a TLS connection** that would be vulnerable to MITM.

**Impact:** Aphoria will detect the **configuration violation**, but we can't show the **runtime consequence** easily.

---

## Next Steps (Day 3)

1. **Run `aphoria scan`** to detect all 8 violations
2. **Analyze results:** Are all 8 detected? Any false positives?
3. **Generate missing extractors** if needed (e.g., for `timeout=0` or `prefetch_count=u16::MAX`)
4. **Re-scan** to verify detection rate ≥90% (8/8 or 7/8)

**Expected scan output:**
```
✗ 8 conflicts detected

Violations:
1. msgqueue-001: timeout=0 (config.rs:20)
2. msgqueue-015: max_queue_size=None (config.rs:26)
3. msgqueue-012: prefetch_count=65535 (config.rs:33)
4. msgqueue-013: ack_mode=AutoAck (consumer.rs:35)
5. msgqueue-018: max_requeue_count=None (consumer.rs:42)
6. msgqueue-002: verify_certificates=false (config.rs:68)
7. msgqueue-003: max_connections=None (config.rs:79)
8. msgqueue-009: blocking in async (processor.rs:38)
```

**Estimated time:** 1-2 hours

---

## Files Created/Modified

```
Cargo.toml                      # Project manifest
src/lib.rs                      77 lines
src/config.rs                   168 lines (5 violations)
src/consumer.rs                 190 lines (2 violations)
src/processor.rs                133 lines (1 violation)
src/connection.rs               123 lines
src/error.rs                    33 lines
DAY2-SUMMARY.md                 This file
```

**Total source:** ~680 lines (excluding tests)
**Total with tests:** ~850 lines

---

## Day 2 Success ✅

**Hypothesis validated:** Can embed **8 intentional violations** in **realistic Rust code** with inline markers for Aphoria detection.

**Key Finding:** Inline markers (`@aphoria:claim[category] invariant -- consequence`) make violations **immediately visible** during code review, even before scanning. This serves as **inline documentation** of safety invariants.

**Ready for Day 3:** Scan the codebase and verify ≥90% detection rate (8/8 or 7/8 violations).
