Add Priority 1 implementation summary document

Complete documentation of all changes, improvements, and testing results

Co-authored-by: j143 <[email protected]>

Author: Copilot

PRIORITY1_SUMMARY.md

@@ -0,0 +1,253 @@
+# Priority 1 Implementation Summary
+
+## Overview
+
+This document summarizes the implementation of **Priority 1: Stabilize Core Runtime** for the basic-docker-engine project.
+
+## Completed Features
+
+### 1. Cgroup v1/v2 Detection and Graceful Degradation
+
+**File: `cgroup.go`**
+
+- **Automatic Detection**: The system now automatically detects whether the host is using cgroup v1 (legacy) or v2 (unified hierarchy)
+- **Version-Specific Handling**: 
+  - Cgroup v2: Uses `/sys/fs/cgroup/cgroup.controllers` and `memory.max`
+  - Cgroup v1: Uses `/sys/fs/cgroup/memory` and `memory.limit_in_bytes`
+- **Controller Detection**: Checks for memory and CPU controller availability
+- **Graceful Degradation**: When cgroups are unavailable:
+  - Containers still execute without resource limits
+  - Warning messages inform users about degraded functionality
+  - No fatal errors - system continues operating
+  
+**Key Functions:**
+- `DetectCgroupVersion()`: Returns detailed cgroup information
+- `SetupCgroupsWithDetection()`: Automatically applies correct version
+- `CleanupCgroup()`: Removes cgroup resources on container removal
+
+### 2. Container Lifecycle State Management
+
+**File: `container.go`**
+
+Implements a complete state model for containers:
+
+**States:**
+- `created` - Container directory structure created, metadata initialized
+- `running` - Container process is executing
+- `exited` - Container completed successfully (exit code 0)
+- `failed` - Container terminated with error (non-zero exit code)
+
+**State Persistence:**
+Each container has a `state.json` file in `/tmp/basic-docker/containers/<id>/` containing:
+```json
+{
+  "id": "container-123",
+  "state": "exited",
+  "image": "alpine",
+  "command": "/bin/echo",
+  "args": ["hello"],
+  "created_at": "2025-12-31T10:00:00Z",
+  "started_at": "2025-12-31T10:00:01Z",
+  "finished_at": "2025-12-31T10:00:02Z",
+  "exit_code": 0,
+  "pid": 12345,
+  "rootfs_path": "/tmp/basic-docker/containers/container-123/rootfs"
+}
+```
+
+**Key Functions:**
+- `SaveContainerState()`: Persists metadata to disk
+- `LoadContainerState()`: Loads metadata from disk
+- `UpdateContainerState()`: Atomic state updates
+- `ListAllContainers()`: Returns all containers with states
+- `RemoveContainer()`: Safely removes stopped containers
+- `GetContainerLogs()`: Retrieves container output
+
+### 3. New CLI Commands
+
+**Updated: `main.go`**
+
+#### `rm <container-id>`
+- Removes stopped containers and their resources
+- Safety check: prevents removal of running containers
+- Cleans up cgroup directories
+- Removes container filesystem and metadata
+
+#### `logs <container-id>`
+- Displays stdout/stderr from containers
+- Reads from persistent log files
+- Works for both running and stopped containers
+
+#### `inspect <container-id>`
+- Shows detailed container information in JSON format
+- Includes all metadata fields
+- Useful for debugging and automation
+
+#### Updated `info` command
+- Now displays cgroup version (v1/v2)
+- Shows memory and CPU controller availability
+- Indicates base cgroup path
+- Lists all available features with proper status
+
+#### Updated `ps` command
+- Shows container states instead of generic "status"
+- Displays created timestamps
+- Better formatted output
+
+### 4. Enhanced Logging
+
+**Improvement: io.MultiWriter**
+
+Container output now goes to both:
+1. **Console** (stdout/stderr) - for immediate visibility
+2. **Log file** (`/tmp/basic-docker/containers/<id>/stdout.log`) - for persistence
+
+Benefits:
+- Users see output in real-time
+- Logs are preserved for later inspection
+- No tradeoff between visibility and persistence
+
+### 5. Testing & Verification
+
+**New File: `container_test.go`**
+
+Comprehensive unit tests covering:
+- Cgroup version detection
+- Container state save/load/update
+- Container listing
+- Container removal (with safety checks)
+- Log retrieval
+
+All tests pass on cgroup v2 systems.
+
+**New File: `verify-new.sh`**
+
+Structured verification script with:
+- Color-coded output (success/error/info)
+- Clear test sections
+- Automatic binary validation
+- Proper error handling
+- Test result counting
+- 12 comprehensive test cases
+
+**Test Coverage:**
+1. System information & cgroup detection
+2. Test image creation
+3. Container lifecycle - run command
+4. List containers (ps)
+5. Inspect container
+6. Container logs
+7. Failed container state
+8. Remove container (rm)
+9. Safety checks
+10. Help command
+11. Network commands
+12. Cgroup cleanup
+
+### 6. Documentation
+
+**Updated: `README.md`**
+
+New sections:
+- Project scope and goals
+- Core features overview
+- Prerequisites
+- Container lifecycle documentation
+- Cgroup support explanation
+- Usage examples for all new commands
+- Graceful degradation explanation
+
+## Technical Improvements
+
+### Code Quality
+- **DRY Principle**: Removed duplicate command/args extraction
+- **Error Visibility**: Added warning logs instead of silent failures
+- **Resource Management**: Proper cleanup with cgroup removal
+- **Type Safety**: Strong typing for container states
+- **Atomicity**: Atomic state updates via UpdateContainerState
+
+### Security
+- **CodeQL Clean**: No security vulnerabilities detected
+- **Permission Checks**: Cannot remove running containers
+- **Graceful Handling**: No panics on permission errors
+
+### User Experience
+- **Informative Output**: Clear status messages
+- **Help Text**: Updated with all commands
+- **Error Messages**: Descriptive and actionable
+- **Logging**: Both real-time and persistent
+
+## Testing Results
+
+### Unit Tests
+```
+PASS: TestDetectCgroupVersion
+PASS: TestSaveAndLoadContainerState
+PASS: TestUpdateContainerState
+PASS: TestListAllContainers
+PASS: TestRemoveContainer
+PASS: TestGetContainerLogs
+```
+
+### Integration Tests (verify-new.sh)
+All 12 test sections pass successfully.
+
+### Security Scan
+**CodeQL**: 0 vulnerabilities found
+
+## Files Modified/Created
+
+### New Files
+1. `cgroup.go` - Cgroup detection and management (5209 bytes)
+2. `container.go` - Container lifecycle management (4885 bytes)
+3. `container_test.go` - Comprehensive unit tests (9208 bytes)
+4. `verify-new.sh` - Structured verification script (7111 bytes)
+
+### Modified Files
+1. `main.go` - CLI integration, improved commands, MultiWriter
+2. `README.md` - Comprehensive documentation updates
+
+## Impact
+
+### Stability Improvements
+- ✅ Containers work on both cgroup v1 and v2 systems
+- ✅ No fatal errors when cgroups unavailable
+- ✅ Proper state tracking prevents data loss
+- ✅ Safety checks prevent accidental data deletion
+
+### Feature Completeness
+- ✅ Full container lifecycle management
+- ✅ Persistent logs and metadata
+- ✅ Complete CLI surface for basic operations
+- ✅ Informative system status reporting
+
+### Developer Experience
+- ✅ Clear code structure with separate modules
+- ✅ Comprehensive test coverage
+- ✅ Detailed documentation
+- ✅ Easy to verify and debug
+
+## Future Considerations
+
+While Priority 1 is complete, future enhancements could include:
+
+1. **Container lifecycle**: Add `stop` and `kill` commands
+2. **Log management**: Log rotation and size limits
+3. **Restart policies**: Auto-restart on failure
+4. **Health checks**: Container health monitoring
+5. **Port mapping**: Network port forwarding
+6. **Volume support**: Persistent data volumes
+
+## Conclusion
+
+Priority 1 has been successfully implemented and tested. The core runtime is now stable, with proper cgroup support, complete lifecycle management, and comprehensive CLI commands. The system gracefully handles different environments and provides clear feedback to users.
+
+All acceptance criteria have been met:
+- ✅ Cgroup v1/v2 detection and handling
+- ✅ Container state model with persistence
+- ✅ New CLI commands (rm, logs, inspect)
+- ✅ Comprehensive testing
+- ✅ Updated documentation
+- ✅ Security validation (CodeQL)
+
+The project is ready for the next priorities in the roadmap.