# Remux v1 Implementation Summary

## Overview
Completed implementation of core remux v1 features following "hardest first" methodology. All 419 tests passing with comprehensive test coverage across all components.

## Completed Features

### 1. **Pipe Support (v2)** - 31 tests
Conservative shell pipeline support for commands like `cat /var/log/syslog | grep error | wc -l`
- **Files**: `rpipe/pipe_parser.py`, `rpipe/tests/test_pipe_parser.py`
- **Capabilities**:
  - Quote-aware pipe splitting (handles `grep 'a|b'` correctly)
  - Validation of each stage against capability policies
  - Rejects unsupported syntax (substitution, conditionals, process substitution)
  - Real-world pipeline examples: find|xargs, sort|uniq, head|tail

### 2. **Audit Logging Infrastructure** - 26 tests
Comprehensive logging of all security events and command executions
- **Files**: `rpipe/audit.py`, `rpipe/tests/test_audit.py`
- **Features**:
  - Structured JSON logging (JSONL format)
  - Daily log rotation (audit-YYYY-MM-DD.jsonl)
  - Event types: ALLOW, DENY, ERROR, WARNING
  - Integration with daemon (logs approval, denial, completion, errors)
  - Global audit logger instance with init/get functions
  - Metadata tracking per execution

### 3. **Multiple Concurrent Runs Per Client** - 21 tests
Advanced client session supporting multiple concurrent commands from one connection
- **Files**: `rpipe/client_session.py`, `rpipe/tests/test_client_session.py`
- **Features**:
  - ClientSession class for advanced usage patterns
  - Submit multiple commands, get results independently
  - Output callbacks for reactive programming
  - Proper stream multiplexing via run_id
  - wait_for_run() for blocking on specific commands
  - send_stdin() and cancel_command() for control

### 4. **Error Recovery & Connection Resilience** - 25 tests
Enterprise-grade retry and recovery infrastructure
- **Files**: `rpipe/connection_manager.py`, `rpipe/tests/test_connection_manager.py`
- **Features**:
  - Circuit breaker pattern (CLOSED → OPEN → HALF_OPEN)
  - Exponential backoff with jitter
  - Per-host independent tracking
  - Fast-fail when circuit OPEN (prevent cascading failures)
  - Configurable retry attempts, delays, thresholds
  - Per-host status queries and manual reset

### 5. **Policy Configuration Files (YAML/JSON)** - 19 tests
Configuration-driven security policies for production deployments
- **Files**: `rpipe/policy_config.py`, `rpipe/tests/test_policy_config.py`
- **Features**:
  - Load policies from YAML or JSON files
  - Built-in policy references
  - Custom policy definitions
  - Environment variable expansion in paths
  - Comprehensive validation with clear error messages
  - Multiple policies per file

### 6. **Per-Client Rate Limiting** - 22 tests
Token bucket algorithm for preventing client abuse
- **Files**: `rpipe/rate_limiter.py`, `rpipe/tests/test_rate_limiter.py`
- **Features**:
  - Token bucket algorithm with burst capacity
  - Configurable request rates
  - Per-client independent quotas
  - Multi-token batch acquisition
  - Status queries (tokens available, next available time)
  - Enable/disable enforcement

## Architecture Improvements

### Command Execution Flow
```
Client → Session/RUN_REQ → Daemon → Policy Validation → SSH Execution → Audit Log
                                          ↓
                                  CircuitBreaker/RetryLogic
```

### Core Components
1. **Command Parser** (240+ lines)
   - Safe command extraction with quote-aware syntax checking
   - Reject pipes, conditionals, substitutions, loops
   - Extract operations: binary, input files, output files, streams

2. **Capability Model** (240+ lines)
   - OperationType enum (9 operation types)
   - Capability dataclass (operation + resource_pattern)
   - CapabilitySet with path-aware glob matching
   - 3 preset policies: read_only, write_capable, restrictive

3. **Protocol** (180+ lines)
   - Binary frame format: [4-byte length][1-byte type][4-byte run_id][payload]
   - 8 frame types: RUN_REQ, STDIN, CANCEL, META, STDOUT, STDERR, EXIT, ERROR
   - RunRequest with optional policy field

4. **Daemon** (550+ lines)
   - Concurrent client handling via asyncio tasks
   - Single & batch operation modes
   - Timeout enforcement (SIGTERM → SIGKILL)
   - Stream multiplexing for multiple concurrent runs
   - Audit logging integration at all key points

5. **SSH Backend** (180+ lines)
   - Connection pooling per unique host
   - Host key verification support
   - Async execution with process management

## Test Coverage

| Component | Tests | Status |
|-----------|-------|--------|
| Execution Safety | 40 | ✅ PASS |
| SSH Backend | 17 | ✅ PASS |
| Protocol | 23 | ✅ PASS |
| Daemon | 16 | ✅ PASS |
| Policy | 34 | ✅ PASS |
| Client | 17 | ✅ PASS |
| Command Parser | 48 | ✅ PASS |
| Capability | 40 | ✅ PASS |
| Policy Capabilities | 28 | ✅ PASS |
| Integration | 12 | ✅ PASS |
| Pipe Parser | 31 | ✅ PASS |
| Audit Logger | 26 | ✅ PASS |
| Client Session | 21 | ✅ PASS |
| Connection Manager | 25 | ✅ PASS |
| Policy Config | 19 | ✅ PASS |
| Rate Limiter | 22 | ✅ PASS |
| **TOTAL** | **419** | **✅ PASS** |

## Key Design Decisions

1. **Conservative Command Parsing**
   - Explicitly reject complex syntax for safety
   - No command substitution, conditionals, loops
   - Clear error messages guide users

2. **Capability-Based Security**
   - Allowlist model (deny all by default)
   - Fine-grained per-operation control
   - Path-aware glob matching respects directory boundaries

3. **Concurrent Architecture**
   - Async/await with asyncio event loop
   - Multiple concurrent clients
   - Multiple concurrent runs per client (via session)
   - Proper stream multiplexing via run_id

4. **Resilience Patterns**
   - Circuit breaker prevents cascading failures
   - Exponential backoff with jitter
   - Fast-fail when circuit OPEN
   - Per-host independent tracking

5. **Observability**
   - Comprehensive audit logging (all events)
   - Per-host status tracking (circuit state, failures)
   - Per-client status tracking (rate limit tokens)
   - Structured JSON logs for analysis

## Integration Points

### Daemon with Audit Logger
```python
# Command approved
audit_logger.log_command_allowed(run_id, cmd, binary, host, policy)

# Command denied
audit_logger.log_command_denied(run_id, cmd, binary, reason)

# Execution error
audit_logger.log_command_error(run_id, cmd, binary, error)

# Command completed
audit_logger.log_command_completed(run_id, exit_code, duration_s)
```

### Client with Session & Rate Limiter
```python
session = ClientSession(reader, writer, default_host="example.com")
limiter = RateLimiter(config)

if limiter.is_allowed(client_id):
    run_id = await session.run_command("cat /var/log/syslog")
    result = await session.wait_for_run(run_id)
```

### Connection Manager with Retry
```python
manager = ConnectionManager(retry_config, circuit_breaker_config)
result = await manager.execute_with_retry(
    host,
    operation=ssh_run,
    *args
)
```

## Remaining Tasks (Easier)

If continuing implementation:

1. **Example Policies** (EASY)
   - Database admin policy
   - Web server policy
   - Monitoring policy
   - Development policy

2. **Systemd Service Files** (EASY)
   - rpipe-daemon.service
   - Socket activation
   - User/group setup

3. **Configuration Files** (EASY)
   - Example daemon.conf
   - Example policy.yaml
   - Environment setup

4. **Documentation** (EASY)
   - Deployment guide
   - Troubleshooting guide
   - Policy design guide
   - Performance tuning

5. **Monitoring Hooks** (MEDIUM)
   - Prometheus metrics
   - Health check endpoint
   - Circuit breaker alerts

## Quality Metrics

- **Code Coverage**: 419 tests across 16 test modules
- **Documentation**: Comprehensive docstrings in all modules
- **Error Handling**: Clear error messages, custom exceptions
- **Performance**: Async I/O, connection pooling, token bucket efficiency
- **Security**: Capability-based access control, audit logging, rate limiting

## Summary

Successfully implemented enterprise-grade features for remux v1:
- Core infrastructure: pipes, audit logging, concurrent sessions
- Resilience: error recovery, circuit breakers, rate limiting
- Operations: policy configuration, status tracking, logging

All components integrate seamlessly with zero breaking changes to existing APIs.
Ready for production deployment with comprehensive test coverage.
