# TAXII 2.1 Compliance Report

## Summary

The TAXII 2.1 client implementation has been validated and updated to comply with the OASIS TAXII 2.1 specification. Key improvements focus on proper envelope format handling, pagination support, and removal of deprecated fields.

## Compliance Status

### ✅ Compliant Features

#### 1. **Discovery Support** (Enhanced from TAXII 2.0)
- Implements discovery endpoint functionality
- Returns required fields: `title`, `api_roots`
- Returns optional fields: `description`, `contact`, `default`
- **NEW in 2.1**: `default` field for specifying default API root
- API roots include version information and max_content_length

#### 2. **Collections Support** (Updated from TAXII 2.0)
- Lists available collections with proper resource structure
- Returns required fields: `id`, `title`, `can_read`, `can_write`
- Returns optional fields: `description`, `media_types`
- **REMOVED in 2.1**: `alias` field (was in TAXII 2.0, removed from spec)
- Supports custom extensions (x_mitre_contents, x_mitre_version)

#### 3. **Get Objects - Envelope Format** (Major change from TAXII 2.0)
- **Returns envelope format** with pagination support
- Required envelope fields:
  - `more` - Boolean indicating if more results available
  - `objects` - Array of STIX objects
- Optional envelope fields:
  - `next` - Pagination token for next page
- **Different from 2.0**: Returns envelope instead of bundle
- Supports all filtering parameters:
  - `added_after` - temporal filtering
  - `match[id]` - filter by object ID
  - `match[type]` - filter by object type
  - `match[version]` - version filtering

#### 4. **Get Manifest - Envelope Format** (Enhanced from TAXII 2.0)
- **Returns envelope format** for consistency
- Manifest entries include:
  - `id` - Object identifier
  - `date_added` - When object was added
  - `version` - Object version
  - `versions` - Version history (NEW in 2.1)
  - `media_types` - Supported content types
- Envelope structure same as get_objects

#### 5. **Add Objects** (Enhanced status response)
- Accepts STIX objects in envelope format
- Enhanced status resource includes:
  - `request_timestamp` - When request was received (NEW in 2.1)
  - All standard status fields (id, status, counts)
  - Detailed success/failure/pending lists

#### 6. **Pagination** (Improved from TAXII 2.0)
- Explicit `next` parameter support in envelope
- Consistent pagination across all list operations
- More intuitive than TAXII 2.0's Range headers

#### 7. **Custom Properties**
- Full support for x_* custom properties
- Preserves MITRE-specific extensions
- Extensibility for vendor-specific fields

### ⚠️ Implementation Notes

1. **Envelope vs Bundle**: TAXII 2.1 uses envelope format for get_objects, while TAXII 2.0 uses STIX bundle format. This is a breaking change handled correctly in our implementation.

2. **Return Type Consistency**: Both get_objects and get_manifest now return dict (envelope format) in TAXII 2.1, improving API consistency.

3. **Library Limitations**: The underlying taxii2client library handles some protocol details internally. Our wrapper ensures spec compliance at the interface level.

## Changes Made

### Major Updates from Previous Version
1. **Removed `alias` field** from collections (not in TAXII 2.1 spec)
2. **Added `default` field** to discovery response
3. **Changed get_objects return type** from list to dict (envelope)
4. **Changed get_manifest return type** from list to dict (envelope)
5. **Added `request_timestamp`** to status response
6. **Added `versions` field** to manifest entries
7. **Proper envelope structure** with `more`, `next`, `objects` fields

### Code Quality Improvements
1. Added comprehensive docstrings with spec references
2. Consistent envelope format handling
3. Improved error handling with graceful fallbacks
4. Better type hints reflecting actual return types
5. Preserved custom extension support

## Key Differences: TAXII 2.0 vs 2.1

| Feature | TAXII 2.0 | TAXII 2.1 |
|---------|-----------|-----------|
| Get Objects Response | STIX Bundle | Envelope with pagination |
| Get Manifest Response | List of entries | Envelope with pagination |
| Collections Field | Has `alias` field | No `alias` field |
| Discovery | Basic API roots | Includes `default` field |
| Pagination | Range headers | Explicit `next` token |
| Status Response | Basic status | Includes `request_timestamp` |
| Manifest Entries | Basic fields | Includes `versions` array |

## Testing

All functionality has been validated through unit tests:
- Correct envelope format for responses
- Proper pagination field handling
- Removal of deprecated fields
- Support for custom extensions
- Error handling scenarios

## Recommendations

1. **Migration Guide**: Users upgrading from TAXII 2.0 to 2.1 should:
   - Update code expecting bundle format to handle envelope format
   - Remove any dependencies on the `alias` field
   - Utilize the improved pagination with `next` tokens
   - Take advantage of the `versions` field in manifest

2. **Future Enhancements**:
   - Implement streaming for large result sets
   - Add support for server-sent events (if supported by server)
   - Enhanced error response formatting per spec

3. **Best Practices**:
   - Always check the `more` field for additional results
   - Use the `next` token for efficient pagination
   - Leverage filtering parameters to reduce payload size
   - Handle both envelope and legacy formats for backward compatibility

## Conclusion

The TAXII 2.1 client implementation is fully compliant with the OASIS TAXII 2.1 specification, providing all core functionality with proper envelope format support, improved pagination, and removal of deprecated fields. The implementation correctly handles the key differences between TAXII 2.0 and 2.1, ensuring smooth operation with modern TAXII servers.